Inspired by the Swedish bread blog Pain de Martin which I recently discovered I decided it was time to have a go at sourdough breads! Although one of my favorite types of bread it’s a long time since I gave it a try and even longer since I actually succeeded. Leaving apple peel covered with water for two weeks in a cool place (15 °C) I got a light apple cider which I used to make a starter some years ago. I followed a recipe from the Norwegian artisan bakery Åpent bakeri and it gave a marvelous bread. But since then I’ve tried to repeat this twice without success. No wonder that even Rose Levy Beranbaum in her book “The Bread Bible” writes that she didn’t intend to include a chapter on sourdough at all. There’s no doubt that sourdoughs are tricky, but I was a litte surprised and disappointed that someone who sets of to write a 600+ page book on bread even considered to skip sourdough… Luckily she changed her mind and the introduction has a fascinating nice-to-know fact: 1 g flour contains about 320 lactic acid bacteria and 13000 yeast cells!

I believe one the reasons why sourdoughs seem to live their own lifes sometimes is that they need to be kept in a warm place. My kitchen isn’t that warm so I figured it was time to use my immersion circulator and give sourdough another chance (who says you can only use immersion circulators for sous vide anyway? – I think my next project will be to make yoghurt!). With a thermostated water bath keeping a sourdough starter at constant temperature is as easy as 1-2-3. But surprisingly I haven’t seen any blogposts yet from people using their sous vide water baths for sourdough starters (although some have built their own water baths for this purpose using aquarium equipment).


Fresh apple peel in water. This particular experiment failed – the cider smelled OK, but there was quite a lot of mould on the surface after two weeks so I didn’t dare to proceed …

It was Martin’s post on an apricot starter that triggered my desire for sourdough (but careful – never close your jar with a rubber as shown in his picture!). I got a bag of dried apricots and gave it a try. There was some bubbling and it smelled quite nice, but the bread dough never rose properly. I later found out that in a comment to the first post and a later post on the same topic it was pointed out that the apricots should not be treated with sulfur dioxide or a sulfite (used to conserve the fruit, appears on labels as E220-228 in Europe). That’s very obvious once you think about it, because the sulfur dioxide/sulfite is there to kill microogranisms and increase shelf life. For a sourdough however you want living microorganisms! The solution to this is to use untreated dried apricots. I haven’t been able to find any yet, but I’ll definitely give it a new try once I find some! Other options of course are to use dried or fresh apples, pears, grapes – preferably not treated with pesticides or sulfur dioxide – as the surface of these fruits are host to many yeasts.

A relatively firm rye starter with 150 g water and 200 g whole grain rye flour (left) shows signs of yeast activity after 24h at 28 °C (right).

Having failed with the apricot starter I decided to give a traditional rye sourdough a try, using a recipe from the book “Brød” (=bread) by “Åpent bakeri”. I got a nice bubbling after 1 day, but the starter was pretty dry. As I discarded a portion and fed more flour and water to the starter it seemd as if it died… I (believe) I followed the recipe very accurately (except for the very first day where I opted for a hydration of 75% instead of 60%), but the final dough never rose, so I had to cheat and add bakers yeast in order to actually get the breads baked. Acid production was fine however and the resulting flavor was very delicious and I got the crumb that I desired! However, with all these problems I figured it was time to turn to the scientific litterature and read more on sourdouhs … More on what I found out in a follow up post.

One last thing: Despite my limited experience with sourdoughs I’ve already been a little annoyed by recipes for starters that require one to discard a significant portion of the sourdough every day before feeding the start with more water and flour. One obvious way around would be to start at a much smaller scale so that every feeding can be done without having to waste any sourdough. In fact Kurt Janz already has a post with detailed instructions on a less wasteful sourdough (and he BTW has one of the most comprehensive sites on sourdough I’m aware of including a sourdough calculator). The only reason I could think of why one perhaps would want to use more than a couple grams of flour to start with would be to outnumber any unwanted yeasts or bacteria from the air or the equipment. Is this the case? Are there any other reasons? To circumvent this one would simple have to work very clean and wash all equipment properly.

Since I got my immersion circulator in December I’ve discovered that there are two critical questions that always come up as I hold a piece of meat in my hands, ready to cook it sous vide: At what temperature should I cook this? And for how long? Despite the fact that two books were published on sous vide last fall it is the short yet comprehensive guide “A Practical Guide to Sous Vide Cooking” by Douglas Baldwin that I’ve found most useful to answer these questions. Those who have followed the eGullet thread on sous vide cooking will probably recognize Douglas Baldwin as one of the major contributors alongside Nathan Myhrvold. Out of curiosity and eager to learn more I therefore emailed Douglas and asked if he would be interested in doing an email interview.

ML: From your homepage I see that you are a PhD student in applied mathematics, how did you become interested in sous vide?

DB: I have always loved to cook. Before last January, though, I mainly cooked slow food. That is when I saw sous vide mentioned in one of Harold McGee’s NY Times articles. Wow. Cooking meat at its desired final core temperature is so obvious! As a mathematician, I kicked myself for never asking “if overcooked meat is bad, what temperature should the meat be cooked at?” A question which many mathematician would instantly answer, “just above the temperature you want it to end up at.”

A quick search of the web led me to the massive eGullet thread on sous vide cooking. While the thread contains a treasure-trove of practical information — especially Nathan Myhrvold’s posts — it left me with a lot of unanswered questions. Being an academic, I turned to the scientific literature for answers; as expected, I found many answers and many more questions.

ML: Your excellent sous vide resource, “A Practical Guide to Sous Vide Cooking” has a wealth of information. What drove you to write this article? And have you ever considered publishing it in a peer reviewed journal?

DB: Thank you. I’m very glad to hear you find my guide to be useful.

As a scientist, I am driven by two things: an insatiable curiosity to learn everything I can about a topic and the desire to freely share what I have learned with the world (so others can extend and build on what I have done). After spending hundreds of hours researching sous vide cooking and discovering how much of the information online was incorrect (and potentially dangerous), I felt compelled to write up what I had learned and post it as soon as possible. I am still actively working on my guide, and hope to complete another major revision in February.

I have not submitted my guide to a peer reviewed journal because its intended audience is chefs and foodies. Though I did ask a number of food scientists to review my guide for technical accuracy, and I was recently asked to referee a paper for the Journal of Food Science.

ML: From your viewpoint, what is the biggest advantage of sous vide over conventional cooking?

DB: Control. Precise temperature control gives incredible choice over the doneness and texture of meat, poultry and fish. Tough cuts can be made tender. Tender cuts are the same perfect doneness from edge-to-edge. Fish and light meat are moist and flavorful. Pork and poultry no longer needs to be brined to be juicy (because they can be made safe without being cooked well-done).

ML: Do you think sous vide cooking will ever become so common that the equipment will be available in regular kitchen stores? And if yes – when will that be?

DB: I don’t think sous vide cooking will ever be so common that immersion circulators will be sold next to microwave ovens. But I fully expect them to be as common as smokers in 5–10 years. Like smoking, sous vide cooking requires a little knowledge and planning — an easy request of the average Khymos reader, but a lot to ask of most consumers. This is unfortunate, because I find sous vide cooking to be convenient, energy efficient, and versatile.

ML: What kind of equipment are you using yourself at home for sous vide? And how often do you typically cook sous vide?

DB: I use a Minipack-torre MVS31 chamber vacuum sealer and a PolyScience 7306C immersion circulator for most of my sous vide cooking. I usually attach the immersion circulator to a full-size countertop food warmer with a lexan lid I made — the lid limits evaporative cooling and the food warmer speeds the (initial) heating of the water and limits heat loss from the bottom and sides of the water bath. I also have a couple Iwatani butane blowtorches, a used PolyScience immersion circulator, a couple PID controllers from Auber Instruments, a Ranco ETC temperature controller, a FoodSaver vacuum sealer, and a bunch of thermocouples and meters from ThermoWorks.

I eat food cooked sous vide almost everyday. As a single guy, I batch cook most my meat in single servings pouches, rapidly chill and then freeze them until needed. While this `cook-freeze’ sous vide is very convenient, the freezing and reheating of the meat does causes small, but noticeable, degradation in taste and texture.

ML: Have you compared DIY bagging with zip-lock bags, food saver bags and vacuum chamber packs? I know that liquids are challenging with the food saver, but does the bagging method affect flavor (or even texture)? Does the small amount of oxygen in the DIY version have any effect?

DB: For meat, different bagging methods have little or no effect on flavor and texture. The primary purpose of bagging is to allow the efficient transfer of heat from the water (or steam) to the food (while still keeping the food and water separated). Sealing the food in a bag has the added benefit of preventing evaporative losses of flavor volatiles and moisture. Even when using a chamber vacuum sealer, the majority of bags have high levels of residual oxygen. The main difference between using a zip-lock bag and a chamber vacuum sealer is the extent to which the bags balloon when heated; (when heated over about 65C/150F) both bags will start to balloon because of the vapor pressure of the liquid in the bag, but the zip-lock bag will balloon more because the residual air in the bag will also expand. It is important that the food is kept from floating to the surface of the water to prevent uneven heating.

While meat can easily be cooked in a zip-lock or food saver bag, fruit and vegetable compression requires a chamber vacuum sealer. Moreover, zip-lock and food saver bagged vegetables balloon excessively in the 85C/185F water bath they are (typically) cooked in because it very difficult to remove all the air in the bag.

Liquid in the bag is indeed problematic when using a food saver, but is easily solved by freezing the liquids before bagging. (Although, I might add that freezing often traps air bubbles in the liquid which cause the bag to balloon more than it would have if a chamber vacuum sealer was used.)

ML: What are your favorites cuts of meat for sous vide?

DB: With the faltering global economy in mind, I love showing off sous vide cooking’s ability to transform inexpensive cuts of meat into something amazing. Consider the humble chuck roast, a flavorful cut of beef which is usually relegated to stews and hamburger because of its abundant connective tissue. Vacuum sealing, cooking for 24 hours at 55C/131F, and searing to a beautiful mahogany color transforms this humble cut into something akin to prime-rib! Pork shoulder vacuum sealed with lard and cooked for 24 hours at 68C/155C, torn into bite-sized hunks and fried in a little oil is always a hit at my dinner parties. Even the the lowly chicken breast can be made into something moist and flavorful by pasteurized in a 60C/140F water bath (see my guide for pasteurization times).

ML: Is there any meat that you would prefer not to cook sous vide?

DB: I don’t like some types of fish cooked sous vide. When cooked too slowly, the enzymes in the fish remain active and cause the flesh to become mushy. [This can be mitigated by using a water bath temperature 5--10C/10--20F higher than the desired final core temperature and using a needle temperature probe inserted through closed-cell foam tape to determine when the fish is done heating.] Also, fish which is not extremely fresh will taste too fishy because the flavor volatiles remain sealed in the bag with the fish —this is a particularly irksome problem for me in land-locked Colorado.

ML: Some critics claim that with sous vide, even though you brown the surface, you loose some flavor since temperature is kept so low (I believe this applies especially for pork). Do you share this experience?

DB: It is a very reasonable concern, but can be mitigated by quickly searing the meat before vacuum sealing and cooking. While the initial Maillard reaction occurs noticeably above 150–180C/300–350F, many of the subsequent reactions can occur at the low temperatures used in sous vide cooking. Personally, I feel searing after cooking is sufficient and almost never take the time to pre-sear my meat.

ML: From your experience, what is most difficult to achieve when cooking sous vide?

DB: A great sear without overcooking the meat. While a blowtorch works wonders on beef and (most) pork, it tends to burn poultry. A pan with a little oil over medium heat (so the oil is between 150–180C/300–350F) works fairly well for poultry, but may overcook the meat before the surface is golden brown.

ML: With Keller’s recent book “Under pressure” and your guide (and an extremely long thread at eGullet) being available now: Which areas would you say need further exploration?

DB: Sous vide cooking is still relatively young and there are hundreds of interesting questions yet to be answered! Some of the questions I’m currently interested in are: How long does it take all the soluble collagen to unfold into gelatin at 55–65C/130F–150F? What is the role of enzymes when cooking at low temperatures for long times? Is it better to thaw the meat or cook it from frozen? If cooking from frozen, how long does it take to heat a piece of meat (such as foie gras) stored at -80C/-110F? Which foods can be frozen or refrigerated after cooking (and for how long?) without significantly degrading taste or texture? How and why should fruits and vegetables be cooked sous vide? Why does fish retain so many more of their essential fatty acids when cooked sous vide (compared with conventional cooking methods)? . . .

In addition to the many unanswered questions, there are also many topics which are understood but have yet to be discussed in sufficient detail. For example, many people’s intuition about clamp and chamber vacuum sealers is wrong. The importance of food shape in predicting heating times has not been discussed — spherical and cylindrical foods heat much faster than slab shaped food. The relatively fast onset of warmed-over-flavor after the food is removed from its vacuum pouch is absent. And even how large and powerful the water bath needs to be for a given quantity of food has not been discussed.

Hopefully I, Nathan Myhrvold, or someone else will have the time and resources to answer all these interesting questions.

ML: Thank you very much!

The suggested temperature range for the roast beef was from 60 °C for a pink interior to 68 °C for grey meat. I settled on 63 °C. I was a little optimistic regarding the timing, so when our guests had arrived and I checked the meat (after 1h 30m) the core had only reached 53 °C. First lesson learnt: meat is a poor heat conductor. I quickly figured that my guests would become very hungry if I were to wait for the core temperature to reach that of the water bath. I therefore turned the water bath up to 68 °C, and put the meat back into the water bath – this time in a normal plastic bag and with a temperature probe at the core. This worked surprisingly well, the pressure of the water pushing out all the air. After another 45 min it had reached 62 °C and I removed the meat from the water bath, saved the juices for the gravy, rubbed the meat with salt and pepper and gave it a quick pan sear with plenty of butter. Despite my bad timing the beef came out extremely moist and tender – I dare say that I have never before achieved such a result with a roast beef in my kitchen! And being my first attempemt at sous-vide with my immersion circulator it was extremely satisfying.

Today I prepared the chicken breast, and I figured that 1h 30m should be sufficient for 700 g of meat. The chicken came out very nice as I served it with fresh pasta, a curry sauce and some salad. Again the meat was moist and tender – and so different from most of the chicken I’ve prepared both at home and been served at restaurants.

I should also mention that I made 68 °C eggs this morning. I left them in the water for 1h. The egg white was very soft – almost runny – whereas the yolk had set but was still very pliable. Comparing this with the eggs over at Fooducation it’s clear that even with constant temperature time does play a role. My 1h @ 68 °C eggs had a white that looked more or less like the white of Erik Fooladi’s 6h @ 65 °C eggs. The are probably several reasons for this, but I guess that the kinetics of protein coagulation are mcuh more complex that one might expect at first. But that’s a different story.

Several comments to my last post asked about pricing and where to buy immersion circulators. Basicallyl any laboratory supplier sells these. And even the simplest models have temperature stability of +/- 0.1 °C or less. Amazon also has a couple of models available from Fischer/Thermo Scientific ranging from around $900-2000.

The products of the Maillard reaction provide tastes, smells and colors that are much desired and lend their charachteristics to a variety of foods. In this post I will focus on the factors that influence how fast the Maillard reaction proceeds. And more specifically I’ll give examples on how the Maillard reaction can be speeded up. This is not about fast food, nor is it about saving time. It’s more about controlling the browning reaction by speeding it up or slowing it down in order to get a desired end result.

The Maillard reaction is, to put it simple, a reaction between an amino acid and a sugar (there’s more on the chemistry at the end of the post). To speed it up you can do one or more of the following:

Chances are you have already utilized this in the kitchen without knowing. When eggs or milk are used for glazing, they act as a protein source for the Maillard reaction, giving a nice brown color. Milk also provides lactose which is a reducing sugar. You’ve probably also observed that temperature does influence browning. Water content is indirectly related to temperature – as long as there is water present, temperature will stay below 100 °C. But once the bread crust dries out the conditions are just right to get the Maillard reaction running.

The same principles are applied to microwaveable pies. The microwaves primarily interact with water and hence only bring the temperature up to the boiling point of water. In order to get sufficient Maillard productcs at these temperatures reducing sugars and amino acids are added to the crust (as exemplified in this patent where dextrose and whey solids are used). Not so surprisingly there is also a patent on how to avoid excessive browning in cookies which calls for addition of a polycarboxylic acid ester to lower pH and hence slow down the Maillard reaction.

Pretzels are an extreme example of how the Maillard reaction can be tweaked. Before baking the pretzels are brushed with lye, a dilute solution of sodium hydroxide, which is very basic. The high pH speeds up the bottleneck of the Maillard reaction (see end of post for details).

A pinch of baking soda can bring out a new taste dimension when browning onions

Another basic ingredient found in most kitchens is baking soda (sodium bicarbonate, NaHCO₃). It’s used as a leavning agent which requires addition of an acid to function. Since it is a weak base, it can be used to increase the pH and hence the speed of the Maillard reaction, for instance when browning onions. This basic task, which isn’t always so easy after all, benefits greatly from a pinch of baking soda (and surprisingly it seems that this hasn’t been done before!). To illustrate this I’ve made a time lapse video of chopped onions being fried with and without baking soda. The frying took 11 min, but things are speeded up about 10x.

Samples taken throughout the experiment are shown in the picture below. Even after 4 min there is a visible difference. After 11 min, the small addition of baking soda has yielded onions which taste remarkably sweet with strong caramel notes, compared to the control which tastes like fried onions.

Another example of how baking soda is used to speed up the Maillard reaction is dulce de leche, a popular sauce/caramel candy in Latin America. It’s made by slowly boiling sweetened milk. Baking soda is not a required ingredient, but is often included. The baking soda gives dulce de leche a darker color and also contributes to the flavor.

Photo by audinou from flickr.com.

It should perhaps be added that baking soda is frequently used in Chinese cooking, for instance in tempura batters and marinades. Once there, the baking soda will certainly speed up the Maillard reaction, but it also affects the texture of meat – I’ll have to return to that topic later.

To round of this post I will briefly touch upon one of the reasons why pH influences the Maillard reaction. The first step involves a reaction between a reducing sugar (depicted as R(C=O)H) and an amino acid (depicted as R’NH2) followed by loss of water to yield a Schiff base. The Schiff base rearranges to the Amadori product (not shown). Of these first steps the formation of the Schiff base is the bottleneck (rate limiting step). The reactivity of the amino acid is influenced by the pH. A simplified reasoning goes like this: At low pH the amino group is protonated, yielding it less nucleophilic. At higher pH, the nitrogen becomes more nucleophilic and at very high pH the amino group can even be deprotonated. It should be noted that the fate of the Amadori product is also in large determined by pH and hence pH will affect more than just the rate, but this is far beyond the scope of this blog post.

Water is a polar molecule, meaning that one end has a small negative charge and the other a small positive charge. Because of this water is a very good solvent for other polar molecules and ions. For instance water is the solvent of choice for substances that provide taste, be it salt, sour, sweet or bitter as these are normally quite polar molecules.

A general rule is that the solubility of molecules and ions increases with the temperature of the water. Extractions are therefore faster if the water is boiling. This is the reason why we use hot water to extract tea leaves or ground coffee beans, even if we want to prepare ice tea or ice coffee. But by lowering the temperature and extending the extraction time we can change the relative proportion of what we extract. It therefore makes perfectly sense that different temperatures are recommended for different types of tea. Using different temperatures for the same kind of tea will of course also influence the flavor profile.

Polar molecules are more easily extracted than non-polar molecules. This is evident if we leave a tea bag for a long time in hot water. The bitter taste is due to the slow extraction of large polyphenol molecules which are less soluble in water. If tea is brewed at a lower temperature, less of the bitter tasting substances will be extracted.

Although water is polar, less polar and even non-polar substances can be extracted with water, especially if the water is boiling hot. You do this every day when prepare coffee. If you take a close look at cup of freshly brewed coffee you can notice small pools of oily substances floating on top of the coffee. The more severe conditions used when extracting coffee to make an espresso ensure that even more oily substances are extracted. Other examples of extraction using water in the kitchen include preparation of stock, soups and gravies.

The principle of extraction is simple, but a number of questions remain largely unexplored with regard to flavor: How do ions affect extraction? What role does pH play? How does temperature influence flavor? There is surprisingly little research on this that includes a sensory evalution.

Eric Devlin over at Home of BBQ interviewed me via email about BBQ and molecular gastronomy. The topic should be of interest to the readers of Khymos as well, so I post the questions and answers in extenso here for your benefit.

Q. Martin, thank you for taking the time to discuss the science of BBQ. Before we get into ‘low and slow’ cooking, can you tell us a bit about your background and your interest in food?
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I have a PhD in chemistry and currently I’m working as a research scientist. When I first became interested in the connection between food and chemistry in the late 90′s, I searched the Internet without finding much information. I did however find some very interesting books in the faculty library, including Harold McGee’s “On Food and Cooking – The Science and Lore of the Kitchen”. Having found books about the subject, I soon started to give popular science presentations. In 2004 I was invited to attend the “International Workshop on Molecular Gastronomy” in Erice, Sicily. This was a great experience and I enjoyed meeting many of the scientists, writers and chefs involved with molecular gastronomy. The website I’ve put up, Khymos, is in many ways what I would have liked to find at the time I became interested in the subject.

Q. Over the past few years we have been hearing quite a bit about how food cooked over a hot flame can have increased carcinogens. Would food that is cooked for a longer period of time over a lower heat be safer?

The carcinogens are formed when meat gets burnt, so although you’d like to use high heat to get the Maillard reaction going (which gives you both flavor and color) you don’t want to overdo it. But even if the meat gets a little burnt, it is a good thing that for the carcinogens, as for all other substances, the poison is in the dose. So if you eat grilled meat every day you should be concerned about this, but for most people I think overeating poses a much greater risk!

Q. Serious BBQ cooks like to produce a ‘bark’ when preparing pork for their pulled pork dishes. Usually the natural ‘bark’ of the meat is enhanced by the sugar found in the dry rubs that are applied. Is there any other method that could be used to achieve or increase those results? Maybe an egg wash prior to cooking?

There are several processes which contribute to the flavor formation. First you have the sugars which caramelize. As you correctly state, this is enhanced by adding sugar to the rubs. Furthermore you have the Maillard reaction were sugars react with amino acids to form a host of compounds which contribute both flavor and color. Even though the Maillard reaction can take place at low temperature (such as in vintage champagne), things really speed up when temperature rises above 110-120 °C. Obviously to reach this temperature you’ll have to get rid of the water first. So using a dry rub makes sense. Apart from that it’s mostly about being patient. Use fresh spices, and where possible whole spices that you ground prior to use. The heat of the grill will toast the spices, thereby intensifying the flavor even more.

I must admit that I have never made nor tasted meat which was prepared with a “bark”, so I don’t dare to go into further details concerning how to improve it. The best thing would be to cook two pieces of meat in parallel, for instance with and without an egg wash to see which one comes out best.

Q. BBQ sauces vary greatly depending on region. Carolina sauces are often thin, while Kansas City and Texas sauces have greater viscosity. If a cook is making a sauce that comes out too thin, what recommendations would you have to thicken it?

You either have to take out some of the water by letting it boil over low heat in a large, wide pot, or you can add a thickening agent such as corn starch. If you use onions, these will help thicken your sauce if you let it boil for a while.

Q. In competitions, some BBQ pit-masters utilize a flavor enhancer called FAB B, which contains msg. The thought behind this additive is that after a judge has consumed numerous samples of the same category of meat, the additive will stimulate the taste buds and help to separate that entry from the rest. Can you recommend any other method of ‘waking the taste buds’ without detracting from the taste?

The problem with this explanation is that if everyone uses FAB, will there be any effect at all? If the idea is to rinse the mouth you would want something acidic which stimulates saliva production, some tannic compounds to bind proteins and perhaps some alcohol to help solubilize fats. Heston Blumentahl at the Fat Duck made a “Green tea sour mousse” from these guidelines.

But even so adaption and habituation occurs in all tasting. I’ve discussed this extensively in a blog post, and the easy answer is variation. Or more scientifically: increased sensing by contrast amplification. Eat something which is as far from meat as you can come, something which is cold, crisp, fresh and acidic (did someone mention a tasty salad?). This will make the next piece of meat taste much better!

Q. FAB contains the following: Hydrolyzed soy protein, vegetable oil (soybean and or corn, cottonseed), sodium phosphates, mono sodium glutamate, autolyzed yeast extract, disodium inosinate and guanylate, xanthan gum. They claim that it enhances natural meat flavors, makes your BBQ juicier, improves texture for better slicing and taste and increases yields. Would you believe that these claims are accurate? Would you recommend other methods to achieve the same results?

I would like to emphasize that MSG’s bad reputation is somewhat undeserved. MSG is the salt of a naturally occurring amino acids and is found in many foods. Parmesan and tomatoes contain lots of it (ever wondered why the Italians sprinkle so much parmesan on their food?). Protein and yeast are excellent sources for MSG and the related compounds listed, so I absolutely believe the claim that FAB will enhance the meaty flavors. When FAB is used in a marinade, the phosphates enhance juiciness and improve texture (more on this later). This is well documented. But even so, every chef should remember that FAB or other products can only make good meat better. Therefore you should pay close attention to the quality of the meat you use.

Q. What is a smoke ring and how is it created? What is the best method of producing a significant smoke ring?

When wood or coal burns, small amounts of nitrogen dioxide is formed which dissolves in the surface of the meat, thereby creating nitrous acid. The acid diffuses further into the meat, and when converted to nitric oxide it reacts with myoglobin to form a stable pink colored molecule.

Q. Is there a point of delineating returns, where a piece of meat will no longer absorb the flavor of the wood that it is cooked with? Are you wasting your time by adding more wood for flavor after a certain point?

Frankly, I don’t know. I think this question should be answered by a chef!

Q. How effective is brining and marinating such as pork shoulder or brisket? How much penetration can you reasonably expect? As competitors often work with a short time frame, is there a way to speed up the results of a marinade? And if alcohol burns off, what’s the advantage of using wine instead of juice? Does the alcohol “do” something before it burns off?

Marinades penetrate meat very slowly, so it should primarily be regarded as a way of adding taste to the surface of the meat (which it does very well). An exception here is chicken and fish which are more easily penetrated by marinades. To speed up marination, use water based, concentrated marinades and leave the meat at room temperature. Piercing the meat with a jaccard will allow the marinade to work from the “inside” as well.

It is perfectly fine to use wine in a marinade. The alcohol will dissolve some fat which can speed up penetration. Wine also contains organic acids which can have a tenderizing effect. Phenolic compounds (tannins) will react with meat proteins to form insoluble complexes which in turn makes meat more juicy and tender (even though the exact reason for this is not understood). Experiments have shown that red wine works better than white in marinades.

An interesting thing with marinades is that to maximize the water retaining capacity of beef, your marinade should not contain both acids and salt as this will in fact lower the water holding capacity! If you go for acids, you can easily add salt later on.

Brining, which is immersing meat in water with about 5% salt, does make sense as the salt helps untangle protein strands. This allows spices to penetrate the meat more easily, and it renders meat juicier. Furthermore it lowers the temperature at which the proteins become “cooked”.

Q. Would searing a piece of meat help to ‘seal’ the juices and allow for a more moist cut?

No. As Harold McGee pointed out, “searing is not sealing”. The only reason to sear meat is to get the Maillard reaction going.

Q. What recommendations would you give to someone that is cooking over wood in a smoker if they wanted to achieve a crisp skin on chicken?

In a smoker the low heat will only be enough to evaporate the water, but only very slowly turn the tough collagen into tender gelatin. To achieve this you’ll need a higher temperature, preferably temperatures around 80-90 °C. But even in a smoker there are a couple of things you can do to improve the crispiness. Use a chicken which has been dry-processed. Alternatively, let the chicken dry uncovered in the fridge for a day. Oiling the skin will improve the heat transfer. You can also pierce the skin to let the juices evaporate.

Q. Barbecuing is often seen as the art of taking a piece of meat that is tough and/or stringy and producing a tender, mouthwatering meal from it. What is it that occurs that renders a tough cut like brisket into a soft, enjoyable meat? Is there anything that can be done to enhance those efforts?

The muscle fibers themselves are tender, but they are held together by connective tissue of which collagen is most abundant. Collagen is tough, but when heated it slowly dissolves and forms gelatin which is very tender. Collagen in young animals dissolves more easily than that of older animals. Collagen starts do dissolve around 70 °C and at 90 °C it dissolves rapidly. But before the temperature get this high enzymes which are present in the meat will help tenderize it. These enzymes lose their activity between 40 and 50 °C, but when you barbecue at low heat the meat will spend quite some time below 40-50 °C.

Q. Why do some meats, after reaching optimal tenderness, seem to get even more tender the longer you cook, while others tend to get tougher if you cook past ideal time?

Preparing meat is more about temperature than time. If you like your beef medium rare you would aim for the center to be 55 °C. Continued heating will cause more proteins to denature and as the contract, water is expelled leaving the dry and rubbery. Unless you have prepared your meat at a temperature very close to the desired temperature of the center, there will be a temperature gradient. So even if you remove the meat from your heating source when the center reaches the desired temperature, the warmer outside of the meat will continue to cook the center as it rests, bringing it outside your desired temperature range. It takes experience to know exactly when to remove the meat from the heat.

Q. What’s happening to the meat during “resting”? Why is this recommended prior to cutting and serving?

Apart from the leveling out of the temperature gradient discussed in the previous question it is a very good idea let meat rest before serving, as this improves the water holding capacity of the meat. This in turn reduces the amount of juice you loose when you carve or slice the meat.

Among dedicated whisky/whiskey drinkers it is customary to add a little water as this “helps to unlock and release the esters, or flavours, from the fats”. Another site claims that dilution helps “breaking down the ester chains and freeing the volatile aromatics”. Does this make sense from a chemical perspective?

When Erik posted me a question some months ago about why we add water to whisky and the chemistry that is involved, I started to speculate about possible mechanisms and discussed them with Erik. Perhaps the most obvious effect is that the alcohol concentration is lowered. High alcohol concentrations anaesthetises the nose and sears the tongue (as the site metioned above correctly states). This is especially true for cask strength whisky which can exceed 60% ethanol. We considered the possibility of a temperature effect. The obvious effect could be achieved by adding water with a different temperature to either cool or warm the whisky. The less obvious effect could be due to a possible release of heat when adding water to a concentrated ethanol solution. Having thought about the different possibilities I did a search and found a very fascinating article: “Release of distillate flavour compounds in Scotch malt whisky”. It was published in 1999, but was new to me and gave me some totally new perspectives on whisky and water. When reading the article, it seems to me that the motivation for adding water to whisky is in fact to mask some aromas and release others!

Malt whisky contains high concentrations of esters and alcohols with long hydrocarbon chains. When water is added, the solubility of these esters and alcohols decreases, and a supersaturated solution results. In extreme cases, the decreased solubility of fat-soluble, volatile organic compounds can lead to clouding due to precipitation of small droplets as seen with anise/liquorise liqours such as Pastis, Pernod, Arak, Raki, Sambuca, Ouzo… (I think I’ll post about that later some time). This can also occur with whiskys that haven’t been chill-filtered. But even in whisky that has been filtered at low temperature a form of “invisible” clouding will occur. The excess of esters and alcohols in the diluted whisky form aggregates (or micelles) which can incorporate esters, alcohols and aldehydes with shorter hydrocarbon chains. Once these compounds are trapped in the aggregates, surrounded by longer chain esters and alcohols, they smell much less since they have a harder time escaping from the liquid! Fortunately, some of the compounds that are trapped have less desireable aromas described as oily, soapy and grassy.

The presence of wood extracts originating from the aging in oak barrels also influences aroma release. One effect is that wood extracts displace hydrophobic (fat soluble) compounds from the surface layer of the whisky (this effect is significant at room temperature when smelling the whisky, less so at 37 °C in your mouth). Furthermore the presence of wood extracts increases the incorporation of hydrophobic compounds into the agglomerates mentioned above.

So far I’ve only discussed the aggregates formed by long chain esters. But studies have shown that when an aqueous solution contains more than 20% ethanol, the ethanol molecules aggregate to form micelles, just like the long chain esters do. These micelles can also trap flavour compounds. Unlike the micelles formed by the long chain esters however, the ethanol micelles break up when diluting the whisky, thus releaseing the entrapped flavour compounds. It is interesting to note that ethanol is less “soluble” in water at high temperatures (ie. the solution is no longer monodisperse). As a consequence, serving whisky “on the rocks” will actually promote the release of flavour compounds from the ethanol micelles. As Mirko Junge commented below, this is one of the very few cases where cooling actually enhances flavour! But the wood extracts found in whisky matured in oak casks supports the formation of ethanol micelles, so as Mirko Junge points out, matured whisky needs more dilution and/or cooling since there are more ethanol micelles.

The over-all effect is a fractionation of volatile compounds upon dilution with water: water insoluble compounds are concentrated in the aggregates (or micelles) of long chain esters, water soluble compounds remain in solution and compounds (probably those which are slightly soluble in water) that were originally trapped in ethanol micelles are liberated.

So after all, the popular notion that addition of water “opens up” the aroma of a whisky is true, but who would have thought that the effect is a combination of “masking” (inclusion of some arome compounds in long chain ester micelles) and “demasking” (opening up of ethanol micelles) and that there even is a temperature effect?

Serving whisky “on the rocks” helps break down ethanol micelles due to the combined effect of cooling and dilution. (Photo by Generation X-Ray at flickr.com)

Feel free to share your experiences with whisky dilution in the comments section below!

(Note: The text has been revised and expanded on June 3rd following the discussion below. Special thanks to Mirko Junge for his valuable comments and for pointing out the importance of the ethanol micelles.)

When invited over to friends for dinner, even before eating, you judge the food by it’s aroma, handing out compliments such as “It really smells nice”! Thankfully, nature is on the cook’s side, because when we prepare food and heat it, volatile aroma compounds are released which trigger very sensitive receptors in our noses. It is generally said that 80% of “taste” is perceived by our nose (what we refer to as aroma), whereas only 20% is perceived by our tongue. How important smell is becomes clear if you catch a cold – suddenly all food tastes the same. Too illustrate the importance of smell, prepare equally sized pieces of apple and pear. Close your eyes, hold your nose and let a friend give you the pieces without telling which is which. Notice how difficult it is to tell them apart. In fact, with a good nose clip you wouldn’t even be able to tell the difference between an apple and an onion! Then, with a piece of either in your mouth, let go of your nose. Within a second you can tell whether it’s apple or pear!

Taste
Our tongue has approximately 10.000 taste buds and they are replaced every 1 to 3 weeks. Their sensitivity increases roughly in the following order: sweet < salt < sour < bitter. In addition to the four basic tastes there is umami, the savory, fifth taste. This taste is produced by monosodium glutamate (MSG), disodium 5’-inosine monophosphate (IMP) and disodium 5’-guanosine monophosphate (GMP). Pure MSG doesn’t taste of much, but can enhance the taste of other foods. There are also some claims of a sixth taste.

A number of taste synergies/enhancements exist. I’ve also included three examples of how flavours can influence taste:

The only general, over-all trend which can be found is that binary tastes enhance each other at low concentrations and suppress each other at higher concentrations (but there are several exceptions!). Do check out “An overview of binary taste–taste interactions” (DOI:10.1016/S0950-3293(02)00110-6) if you’re interested in more details on binary taste interactions. I’ve tried to visualize taste enhancements (green) and suppresions (red) in the following figure using arrows to indicate the direction. For example, salt suppresses sweetnes at high concentrations.

In addition to taste, our tongue also percieves texture, temperature and astringency. An interesting thing about the temperature receptors is that they can be triggered not only by temperature, but also by certain foods. The cold receptor is triggered by mint, spearmint, menthol and camphor. There is even a patented compound, monomenthyl succinate, that triggers the cold receptor, but without the taste of menthol. It’s marketed under the name Physcool by the flavour company Mane.

Substances such as ethanol and capsaicin trigger the trigeminal nerve, causing a burning sensation. Capsaicin also triggers the high temperature receptors of the tongue, hence the term “hot food” which can refer both to spicy food and food which is very warm. For a general article about taste, check out “Taste Perception: Cracking the Code” (DOI:10.1371/journal.pbio.0020064, free download).

Flavour
Our nose has about 5-10 million receptors capable of detecting volatile compounds. There are about 1000 different smell receptors and they allow us to distinguish more than 10.000 different smells – perhaps as many as 100.000! In order for us to smell something, the molecule needs to enter our nose at a concentration sufficient for us to detect. Aroma compounds are typically small, non-polar molecules. The fact that they are small means they will have low boiling points – they are volatile and spread rapidly throughout a room. They are often referred to as essential oils and are very soluble in fat, oil and alcohol. These aroma compounds generally not soluble in water, but there are also water soluble aroma compounds; just think of a well prepared stock – no fat but lots of taste and aroma!

A challenge with aroma molecules is that they should remain intact during storage and not be released until cooking (or even better, until consumption). A example would be to install a Liebieg condenser over your pot. Dylan Stiles has explored this in his column Bench Monkey by placing a bag of ice on top of the lid. He claims that his roommates prefereed the curry which has been cooked under “reflux conditions”. The study was performed in a double blind manner (which I will come back to in part 8 of this series).

Because aroma compounds are volatile, spices should be obtained whole and stored in tight containers away from light. If possible, fresh herbs should be used. The flavour of herbs and spices can be extracted by chopping or grinding to increase the surface area. To speed up grinding in a mortar you can add a pinch of salt or sugar.

Heat can help extract flavour (just think of how we brew tea or coffee), but will also evaporate volatile compounds, so a general advice would be to add spices at the start and herbs towards the end of the cooking time. Some herbs can even be sprinkeled over the food just before serving. In Southeast Asia (and especially India) it is quite common heat spices in a dry pan or in oil. This matures flavours and allows reactions to occur (possibly Maillard reactions). Coarse spices should be added earlier than finely ground spices.

In addition to adding flavour using spices, herbs and other foods, we can also use heat to create new flavours. When sugar is heated, caramel is formed. And if a reducing sugar is heated in the presence of an amino acid, they react and form a host of new flavour compounds in what is known as the Maillard reaction. Caramelisation and the Maillard reaction are known as non-enzymatic browning. Enzymatic browning on the other hand is detrimental to many fruits (such as apples and bananas), but there are a few exceptions. Enzymatic browning is essential in the production of tea (black, green, oolong), coffe, cocoa and vanilla, although this is rarely attempted in kitchen.

Another source of flavour is fermentation. It refers to a process were sugar is converted to alcohol and carbon dioxide by the action of a yeast. In the process a number of flavour compounds are formed as well which is why this is of great interest also from a molecular gastronomy viewpoint. Some examples of fermented products include wine, beer, cider and bread. Fermentation also refers to the process where some bacteria produce lactic acid. Some examples of foods resulting from lactic acid fermentation are yoghurt, kimchi and pickled cucumbers.

Flavour pairing
Cookbooks and recipes throughout the world are the result of billions of experiments. As a result, some very good combinations of herbs and spices have been discovered. Some of these mixtures have even been given names of their own and it is fascinating how easily one can forget that curry for instance is a mixture of spices. Wikipedia has a wonderful overview of herb and spice mixtures from all over the world. I must admit I only new a fraction of these:

Adjika | Advieh | Berbere | Bouquet garni | Buknu | Cajun King | Chaat masala | Chaunk | Chermoula | Chili powder | Curry powder | Djahe | Fines herbes | Five-spice powder | Garam masala | Garlic salt | Harissa | Herbes de Provence | Khmeli suneli | Lawry’s and Adolph’s | Masala | Masuman | Mixed spice | Niter kibbeh | Old Bay Seasoning | Panch phoron | Quatre épices | Ras el hanout | Recado rojo | Shake ‘N’ Bake | Sharena sol | Shichimi | Spice mix | Tajín | Tandoori masala | Tony Chachere’s | Za’atar

A book which I’ve found to be very useful when combining flavours is “Culinary artistry” by Andrew Dornenburg and Karen Page. It is the most comprehensive book about flavour pairing that I’m aware of, and I would say it is indispensible for someone who likes to cook without a cookbook. It has lists of basic flavors contributed by various foods. For example a sweet taste is contributed by foods such as bananas, beets, carrots, coriander, corn, dates, figs, fruits, grapes, onions, poppy seeds, sesame and vanilla (plus sugars and syrups of course). It has lists of “flavor pals”, a term attributed to Jean-Georges Vongerichten. For example, the flavour pals of ginger are allspice, chiles, chives, cinnamon, cloves ,coriander, cumin, curry, fennel, garlic, mace, nutmeg, black pepper and saffron. By far the most extensive part of the book are listings of food matchings. An illustrative example is pork which combines well with (classic/widely used combinations in bold):

apples, apricots, bay leaves, black beans, beer, brandy, cabbage, Calvados, dried sour cherries, clams, Cognac, coriander, cream, cumin, fennel, fruit, garlic, ginger, hoisin sauce, honey, juniper berries, lemon, lime, marsala, molasses, mustard, onions, orange, parsley, black pepper, pineapple, Chinese plum sauce, plums, prunes, quinces, rosemary, sage, sauerkraut, soy sauce, star anise, tarragon, thyme, vinegar, walnuts, whiskey, white wine

Despite the abundance of combinations, I dare say that little is understood about the science behind these flavour pairings. Why do these combinations of herbs and spices go particularily well together? Is it all about getting used to the combinations, so that we learn to like them? What influence does the complexity of the flavour play? These are easy questions that probably have rather complex answers.

Very recently a different approach to flavour pairing has emerged. If two foods share one or more key odorants, chances are that they will go well together. The first step towards finding new pairings would be to identify key odorants. More info on key odorants can be found in the article “Evaluation of the Key Odorants of Foods by Dilution Experiments, Aroma Models and Omission” (DOI: 10.1093/chemse/26.5.533, free download). I’ve initiated the food blogging event “They go really well together” (TGRWT) to explore new flavour pairings and develop new recipes. There are also several blogposts with interesting comments on about flavour pairing.

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Check out my previous blogpost for an overview of the tips for practical molecular gastronomy. The collection of books (favorite, molecular gastronomy, aroma/taste, reference/technique, food chemistry) and links (webresources, people/chefs/blogs, institutions, articles, audio/video) at khymos.org might also be of interest.

4. Learn how to control the texture of food

Taste and flavour normally get more attention when food is discussed, but the texture of food is equally important and our tongue is very sensitive, not only to taste and temperature, but also to the texture of food. The texture of food determines it’s mouthfeel and it is related to many physical properties of the food. Wikipedia lists the following aspects of mouthfeel (click to see the full description of each aspect) which can be useful when analyzing food:

Adhesiveness, Bounce/Springiness, Chewiness, Coarseness, Cohesiveness, Denseness, Dryness, Fracturability, Graininess, Gumminess, Hardness, Heaviness, Moisture absorption, Moisture release, Mouthcoating, Roughness, Slipperiness, Smoothness, Uniformity, Uniformity of chew, Uniformity of bite, Viscosity, Wetness

I will barely scratch the surface of how texture can be controlled by highlighting a couple of topics and point you to further resources. Hopefully it will spark your interest and give some new ideas for you to play with in the kitchen. Those interested in a comprehensive review of food texture are referred to the CRC handbooks on food texture (volume 1: semi-solid foods, volume 2: solid foods).

What determines the texture of food?
Put very simple, it’s the relative amounts of air, liquid and solids that determines the texture of food. This is complicated by the fact that liquids have different viscosities. Furthermore the air, liquid and solid ratio is not necessarily constant. A liquid can solidify or evaporate, solids can melt or dissolve, and air bubbles can escape during cooking or storage. An elegant but quite abstract way of describing the complicated mixtures of air, liquids and solids found in food, is to use the CDS formalism (CDS = complex disperse systems), introduced by Hervé This.

(Photo by Subspace at flickr.com)

How can texture be controlled and changed?
Texture can be controlled by temperature, pH, air/liquid/solid ratio, osmosis, hydrocolloids and emulsifiers – to mention a few. Here’s some examples:

(Photo by Trinity at flickr.com)

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Check out my previous blogpost for an overview of the tips for practical molecular gastronomy. The collection of books (favorite, molecular gastronomy, aroma/taste, reference/technique, food chemistry) and links (webresources, people/chefs/blogs, institutions, articles, audio/video) at khymos.org might also be of interest.

You can also do it the other way around. Let’s say you have boiling water and you know that your tap water is approximately 10 °C. If you want water at approximately 37 °C, you can do as follows:

Start by writing what you have to the left (100 °C and 10 °C) and what you want in the middle (37 °C). Subtract: (100-37) = 63 and (37-10) = 27. And voilá – you need 27 parts water at 100 °C and 63 parts at 10 °C (and 27:63 simplifies to 3:7 which is what we found above). Now of course if you really wanted water at 37 °C, you would simply put your finger in to see if it’s at body temperature…

Are there any practical applications of this? Yes – a simple, but elegant way to prepare fish would be to drop a fish of known weight and temperature (fridge @ 4 °C or freezer @ -18 °C) into water that has been brought to boil. Cover pot and turn off heat. The amount of water would be calculated based on the desired temperature of the fish. We are assuming here that there is no heat loss to the surroundings, which of course isn’t quite true. How fast pot of water will cool depends on how much water you use and on the pot. This can be corrected for, and luckily someone has already done it. More on this in my post on how to cook fish in cooling water.

We can apply the temperature calculation from above to figure out roughly what the temperature will with this cooking method. 800 g of fish from the fridge (4 °C) and 2,4 L of boiling water gives a temperature of (0,8 x 4 °C + 2,4 x 100 °C) / 3,2 = 76 °C. The cooling curves for a pot with 2,5 L of water suggest a temperature loss of 15-20 °C in 30 min which would bring us down to 55-60 °C which – considering that no thermometer is used – is quite good.