Thomas Keller, known from the French Laundry, Bouchon and per se, has written the book “Under Pressure - Cooking Sous Vide” (the Under Pressure title was also used by NY Times in a 2005 feature article on sous vide). According to the publisher, Keller and his chefs de cuisine have blazed the trail to perfection through years of trial and error and they show the way in this collection of never-before-published recipes from his landmark restaurants.

The book “Sous-Vide Garen im Vakuum” (Sous vide cooking under vacuum) by Viktor Stampfer (known from the Ritz-Carlton in Dubai) has received much less attention, but certainly deserves to mentioned. The title is in German, but do not despair - it seems to be a bilingual edition with German and English text (can anyone confirm this?), but so far it’s only available for preorder from the German Amazon. According to the publisher the book gives an introduction to the equipment used including sealing devices and recommended temperatures for cooking together with numerous recipes.

These are not the first books to appear on sous vide - enthusiasts have probably obtained one or more of the books by Roca, Farber, Ghazala, Leadbetter, Choain/Noël and Calmejane/Barrier - but I’m quite sure that the new books will complement these very nicely, and they will certainly be more available as several of the others have unavailable for some time.

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I’m grateful for feedback from several readers pointing out that the size of gelatin sheets is made to compensate for different bloom strengths. In other words, one gelatin sheet will gel a given amount of water, regardless of the size of the gelatin sheet. To the best of my knowledge, this convention seems to have been adopted by most gelatin producers.

All gelatin based recipes have been updated to reflect this and most of them now give the amount of gelatin both in grams (for a platinum type, 240 bloom gelatin) and in number of sheets. I’ve also included a formula for conversion between different bloom strengths. This formula differs from what has been published earlier (no square root), but by testing the formula for given gelatin sheet bloom strengths and weights I got better results by simply multiplying the mass by the ratio of the bloom strengths. If you know more about these formulas, please leave a comment or email me.

Checking the gelatin recipes I discovered that the recipe “Strawberry spheres” originally called for “Sosa vegetable gelatin” which is not gelatin but a mixture of carrageenan and locust bean gum which are dispersed with maltodextrin. Since the exact amount of carrageenan and locust bean gum are not known I’ve deleted the recipe (but I’m sure you could achieve the same coating effect with plain gelatin, perhaps a 3-4% solution to render it viscous so it will cling the the spheres).

Thanks to feedback from a reader there is also recipe now for agar filtration (based on a Spanish forum post). This works just like gelatin filtration, but is much faster. Apparently you get more or less the same results with regard to clarity, flavor and color.

If printing the collection, make sure the hydrocolloid properties table is rotated so it prints correctly. This table is presented in landscape format. The right most column of the first page is gelatin - if you don’t see it, try printing these pages again. The pages are optimized for printing on A4. If printing on Letter sized paper, make sure you check the “resize” or “fit to paper” option in your pdf reader.

Thank you for comments, corrections, recipes and other feedback! As always, I can be reached at webmaster a t khymos d o t org.

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The soda fountain (Diet Coke + Mentos) has been around the net for quite a while with some spectacular videos available, and it has even made it into a news paper cartoon. People go crazy about this and the largest number of simultaneous fountains is steadily increasing.

Despite the interest, only now did a scientific paper appear on the subject. Many have speculated about what causes the reaction between Mentos and Diet Coke, and some have focused on possible acid-base reactions taking place. Mythbusters investigated this in 2006 (watch episode) and came up with the following factors that contribute to the bubble formation:

Diet coke

• carbon dioxide is what makes the bubbles form in the first place
• in synthetic mixtures aspartam, caffeine and potassium benzoate where shown give better fountains

Mentos

• the most important property is the rough surface which provides plenty of nucleation sites for bubble formation
• the density makes them sink which is ideal as the bubbles formed at the bottom of the bottle help expel much more soda
• mentos contains gelatin and gum arabic which could also reduce surface tension

In the paper “Diet Coke and Mentos: What is really behind this physical reaction?” by Tonya Shea Coffey the findings of the Mythbuster teams are largely confirmed.

By measuring contact angles it was shown that aspartame and potassium benzoate reduce the surface tension of water. Aspartame is a winner, and as an extra benefit clean up is much easier with Diet Coke than sugared Coke. The amount of caffeine however is too low to have any effect. The roughness of the Mentos surface was studied with special microscopes (see picture below). Fruit Mentos have smooth patches, but the coating is not uniform and contrary to the Mythbuster experiment normal Mentos and Fruit Mentos performed equally well with regards to foam formation. The roughness of the Mentos surface was inbetween that of rock salt and the Life savers which suggests that roughness is not a single factor determining the reaction. The Mentos surface is covered with gum arabic which reduces surface tension, and experiments showed that even without Mentos, gum arabic could cause a reaction to occur. It is the combined effects of reduced surface tension (due to ingredients in Diet Coke and Mentos) and the rough surface of Mentos which is the key to understand the reaction.

As expected, the article also confirms that the reaction is more vigours at higher temperatures (i.e. solubility of carbon dioxide deacreases with increasing temperature). It was also shown that Mentos sink faster to the bottom of a 2 L bottle compared with rock salt, Wint-O-Green Life savers and sand (this is a function of size and density, not only density). When bubbles are formed at the bottom of the bottle the bubble has more time to grow as it rises. This causes a more explosive reaction and more soda is expelled from the bottle.

The picture shows scanning electron microscopy images of Mint Mentos (a) and (c) and Fruit Mentos with a candy coating (b) and (d). The scale bars in each image represent the lengths (a) 200 μm, (b) 100 μm, (c) 20 μm, and (d) 20 μm. Fruit Mentos has smooth patches, but the coating is not uniform. (Reprinted with permission from Coffey, T. S, American Journal of Physics, Vol. 76, Issue 6, pp. 551-557, 2008. Copyright 2008, American Association of Physics Teachers)

The question which lingers on my mind is whether Diet Coke and Mentos represent the optimal combination of ingredients to create a soda fountain. With regard to convenience, I guess the answer is yes. But perhaps it’s possible to create an even more powerful reaction? Since lowering the surface tension of water is important, I’m wondering if it would be possible to find a surfactant that could be added without setting the reaction off? Mentos would of course still be needed for the rough surface to provide nucleation sites. In the above mentioned study addition of diluted dish washing liquid was enough to give a pretty good reaction, so this is not an option. But perhaps a couple of drops right on the Mentos surface would work? I definitely need to try this some time.

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Ethanol is a molecule with both a polar and a non-polar end, so it’s properties are somewhat in between those of water and oil (which will be the topic of the next post in this series about extraction). This is easily illustrated by the fact that both water and oil are soluble in pure ethanol (albeit not at the same time - adding water to ethanol reduces the solubility of oil). Many taste molecules are polar whereas most aroma molecules are non-polar, and the good thing is that ethanol can be used to extract both groups of compounds.

I belive the most widespread use of ethanol for extractions in the kitchen is for sweet liqueurs where fruits or berries are extracted with ethanol and the extract is sweetened with sugar. The word liqueur comes from the Latin word liquifacere which means “to dissolve”, and this is essentially what happens - the ethanol and water extract and dissolve flavor and color from the fruit.

Some also make their own spirits by infusing spices and herbs. One example is aquavit which is based on carraway combined with a number of other spices for complexity such as dill, coriander, anis, fennel, liquorice, cardamom and lemon. Commercial aquavits are distilled, but at home it’s suffices to filter of the spices and herbs. As a result home made aquavits are always amber colored (such as the one pictured in a previous post).

For extractions like these, one always uses diluted ethanol, typically 30-60% ethanol in water would be used, and most often somewhere around 40-50%. One reason for this is that higher concentrations of ethanol would extract to many bitter and astringent compounds. Another reason is that in some (most?) countries it is illegal to posess, buy and/or sell ethanol at higher concentrations for consumption (pure ethanol for technical use is denatured if sold in normal stores and requires special permissions if used in laboratories).

Apart from the steping herbs and spices in ethanol to make liqueurs, the only other example of relevance for the kitchen I can think of is for extraction of vanilla beans to make pure vanilla extract. This is quite surprising actually, and although I really don’t know if ethanol is used for extraction in professional kitchens, it is my impression that ethanol extractions are underutilized in the kitchen.

There are several benefits with ethanolic spice and herb extracts:

• fast - no need to wait for the spices to be extracted since they have been “pre extracted”, you can taste the dish immediately and add more spice extract if necessary
• no residues - seeds, leaves or bark are filtered off before use
• convenient - spice extracts are an excellent way of adding clean, concentrated aromas
• stable - spice extracts keep very well (although the storage may also change the flavor profile somewhat and “mature” the flavor)
• new flavors - some spices and in particular herbs will change upon extraction and storage and this can open up new possibilities (this needs quite some experimentation though - some herb flavors change to the worse…)

What are your experiences with ethanol extractions in the kitchen?

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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.

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I recently became aware of an excellent site focusing solely on liquid nitrogen ice cream! Ever heard about “The institute for liquid nitrogen ice cream experimental studies” or TILNICES for short? They’re located at the Department of Chemistry at the Tennessee Technological University. It seems that the site is still under construction, but several recipes are already available plus a number of papers (available for download as pdf files).

[Thanks to John Placko on the MG mailing list for mentioning the site]

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9. Keep a written record of what you do!

Wouldn’t it be a pity if you couldn’t recreate that perfect concoction you made last week, simply because you forgot how you did it? Last year I made a vegetable soup to which I added garam masala and pepper. I was cooking ad lib, adding a little of this and that without taking notes… Which is annoying, because it turned out very nice! It had a remarkable aftertaste which gave me a somewhat dry feeling on the back of the tongue and it reminded me of mangoes. Even immediately after the meal I wasn’t able to recall all the ingredients.

As an undergraduate student I took an organic chemistry lab course, and I remember we were told not to use post it notes or small pieces of paper for taking notes. Everything should be recorded in a proper journal or - if necessary - small note books. Having finished my Ph.D. a couple of years later, I can only testify to this. Everything you do - be it in the lab or in the kitchen - should be recorded immediately in a journal. It’s amazing how something that was obvious one day, slips your mind a week or month later.

There is a wonderful Donald Duck story by Volker Reiche entitled “The soul of science” (the original appeared in 1981 in the Dutch Donald Duck magazine). At a point “Professor Duck”, who actually works as a janitor in a lab, utters the words “Careful notes are the soul of science” as he is caught experimenting. This is true also for the kitchen and experimental cooking. A German translation of the story was reprinted in the article “Das Leiden des cand. chem. Donald Duck” (open access) in case you want to read the whole story.

Careful notes are also the soul of kitchen science!

When taking notes it’s essential that you are able to re-cook the dish yourself. But if no one else is, the notes are of limited value. The biggest source of uncertainty in the kitchen is the widespread use of volume for measuring powders. This can best be illustrated by the question: How much does a cup of flour weigh?

I bumped into this when I began baking no-knead bread (recipe). I converted the recipe to metric units using an online calculator, but the no-knead bread wasn’t a huge success. The problem was that there is no simple answer to the question “How much does a cup of flour weigh?”. Cooking conversion online states that a cup of all-purpose flour weighs 99 g. King Arthur Mills claim that all their flours weigh 113 g/cup. USDA states 125 g/cup and Gold Medal 130 g/cup. Some cookbooks have settled at 140 g/cup (apparently because this is about half way between a loosely and densly packed cup) and if the flour is hard packed you can reach 160 g/cup. In other words - when following a recipe you would need to know how the volume of flour was measured in order to use exactly the same amount of flour. Some recipes call for “spoon and level” or “scoop and level”, but many do not include any information about this.

My recommendation is to weigh all dry ingredients (and preferably also the wet ingredients). A normal digital kitchen scale typically has a resolution of 1 g with an accuracy of +/- 5 g and they are quite affordable. Weighing liquids is also far more accurate than the average volume measurement in the kitchen. If the scale has a “tara” function it’s also much faster as you can zero the display after each ingredient you add. It shouldn’t come as a surprise that I’m not the only chemist advocating weight measurements in kitchen. And it’s not difficult finding other sites in favor of weight measurements either.

It therefore puzzles me why recipes that call for the following are still so abundant:

1 pack of instant yeast
1 envelope unflavored gelatin
1 gelatin sheet (see comment #4-5)
1 sachet powdered pectin
1 tablespoon liquid pectin
1 stick of butter
… and the list goes on

The only exception to the general advice on weighing ingredients is when very small quantities are used. This could be spices, food coloring or hydrocolloids. With normal kitchen scales, you’ll be better of using volume measurements for amounts less than 5 g (equal to a teaspoon if measuring water). Otherweise it’s worthwhile mentioning that scales with a 0.1 g and 0.01 g readout are getting cheaper and cheaper.

*

There is a summary of the “10 tips for practical molecular gastronomy” posts. The collection of books (favorite, molecular gastronomy, aroma/taste, reference/technique, food chemistry) and links (people/chefs/blogs, webresources, institutions, articles and audio/video) at khymos.org might also be of interest.

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Texture - A hydrocolloid recipe collection
It’s a pleasure for me to announce that an updated version of the hydrocolloid recipe collection is available for free download as a pdf file (73 pages, 1.8 Mb).

What’s new?
Several new recipes have been added (now counting more than 220 in total), including recipes with cornstarch, guar gum, gum arabic, konjac and locust bean gum. All in all 14 different hydrocolloids are included (plus lecithin which technically isn’t a hydrocolloid). In each section recipes are now sorted according to the amount of hydrocolloid used. The appendix has been updated with tables for comparison of hydrocolloid properties, hydrocolloid densities and synergies. The perhaps biggest change is that all recipes have been indexed according both to the texture/appearance of the resulting dish and according to the hydrocolloid used. Let’s say you want to make spheres, this index will show you which hydrocolloids can be used (that’s right - there are other possiblities than sodium alginate) and list the example recipes.

Foreword
A hydrocolloid can simply be defined as a substance that forms a gel in contact with water. Such substances include both polysaccharides and proteins which are capable of one or more of the following: thickening and gelling aqueous solutions, stabilizing foams, emulsions and dispersions and preventing crystallization of saturated water or sugar solutions.

In the recent years there has been a tremendous interest in molecular gastronomy. Part of this interest has been directed towards the “new” hydrocolloids. The term “new” includes hydrocolloids such as gellan and xanthan which are a result of relatively recent research, but also hydrocolloids such as agar which has been unknown in western cooking, but used in Asia for decades. One fortunate consequence of the increased interest in molecular gastronomy and hydrocolloids is that hydrocolloids that were previously only available to the food industry have become available in small quantities at a reasonable price. A less fortunate consequence however is that many have come to regard molecular gastronomy as synonymous with the use of hydrocolloids to prepare foams and spheres. I should therefore emphasize that molecular gastronomy is not limited to the use of hydrocolloids and that it is not the intention of this collection of recipes to define molecular gastronomy.

Along with the increased interest in hydrocolloids for texture modification there is a growing scepticism to using “chemicals” in the kitchen. Many have come to view hydrocolloids as unnatural and even unhealthy ingredients. It should therefore be stressed that the hydrocolloids described in this collection are all of biological origin. All have been purified, some have been processed, but nevertheless the raw material used is of either marine, plant, animal or microbial origin. Furthermore hydrocolloids can contribute significantly to the public health as they allow the reduction of fat and/or sugar content without loosing the desired mouth feel. The hydrocolloids themselves have a low calorific value and are generally used at very low concentrations.

One major challenge (at least for an amateur cook) is to find recipes and directions to utilize the “new” hydrocolloids. When purchasing hydrocolloids, typically only a few recipes are included. Personally I like to browse several recipes to get an idea of the different possibilities when cooking. Therefore I have collected a number of recipes which utilize hydrocolloids ranging from agar to xanthan. In addition to these some recipes with lecithin (not technically a hydrocolloid) have been included. Recipes for foams that do not call for addition of hydrocolloids have also been included for completeness. Some cornstarch recipes have been included to illustrate it’s properties at different consentrations. Recipes where flour is the only hydrocolloid do not fall within the scope of this collection as these are sufficiently covered by other cook books.

All recipes have been changed to SI units which are the ones preferred by the scientific community (and hopefully soon by the cooks as well). In doing so there is always uncertainty related to the conversion of volume to weight, especially powders. As far as possible, brand names have been replaced by generic names. Almost all recipes have been edited and some have been shortened significantly. To allow easy comparison of recipes the amount of hydrocolloid used is also shown as mass percentages and the recipes are ranked in an ascending order. In some recipes, obvious mistakes have been corrected. But unfortunately, the recipes have not been tested, so there is no guarantee that they actually work as intended and that the directions are complete, accurate and correct. It appears as if some of the recipes are not optimized with regard to proper dispersion and hydration of the hydrocolloids which again will influence the amount of hydrocolloid used. It is therefore advisable to always consult other similar recipes or the table with the hydrocolloid properties. The recipes have been collected from various printed and electronic sources and every attempt has been made to give the source of the recipes.

Since recipes can neither be patented nor copyrighted, every reader should feel free to download, print, use, modify, and further develop the recipes contained in this compilation. The latest version will be available for download from the static Khymos site and will also be announced here. I would like to thank readers for giving me feedback and suggestions on how to improve the collection. Feedback, comments, corrections and new recipes are always welcome at webmaster (a t) khymos ( dot ) org.

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Rob Mifsud, perhaps best know for his Hungry in Hogtown blog has interviewed Hervé This. At the end of the interview Hervé lists 10 elements of basic kitchen knowledge. Some may seem obvious, but they are not, according to Hervé. Here’s the list so you can judge by yourselves:

1. Salt dissolves in water.
2. Salt does not dissolve in oil.
3. Oil does not dissolve in water.
4. Water boils at 100 °C (212 °F).
5. Generally foods contain mostly water (or another fluid).
6. Foods without water or fluid are tough.
7. Some proteins (in eggs, meat, fish) coagulate.
8. Collagen dissolves in water at temperatures higher than 55 °C (131 °F).
9. Dishes are dispersed systems (combinations of gas, liquid or solid ingredients transformed by cooking).
10. Some chemical processes - such as the Maillard Reaction (browning or caramelizing) - generate new flavours.

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Measuring powders by volume has serious limitations (more on this later in an up-coming post), but one great advantage is that for small quantities going by volume can sometimes be more accurate than weighing them. At least when you work in a kitchen and don’t have access to professional lab scales. When a scale shows 0.1 g, the true weight could be anywere from 0.05-0.149 g due to rounding (that’s ± 50%!). Not to mention the fact that cheap balances aren’t always very accurate for such small amounts, even though they feature a 0.1 g resolution.

I’m currently working on a major revision of the collection of hydrocolloid recipes. One thing I would like to include is a table with densities of the hydrocolloids and chemicals used. When the densities are known, it’s possible to give some rough advice for what volume to use (this on-line conversion calculator has the densities of many common ingredients). This could ease small scale preparations. It will also make it easier to calculate the percentage of hydrocolloid used in recipes where the amount is given by volume. I’ve measured the hydrocolloids I have at hand, but I need your help to fill out the table and repeat the measurements I’ve done. With enough measurements I could also do some statistics and make a plot. I’m also interested to see if there is much variation between different brands.

How to determine the density:

1. Find a suitable measuring spoon, cup, shot glass, container - whatever you have - with a volume of at least 10 mL (I used one of about 30 mL).
2. Put the empty container on the balance and use the tara function.
3. Fill completely with water and weigh again. The difference gives you the exact volume (for water 1 g = 1 mL).
4. Dry the container, put it on the balance and use the tara function.
5. Spoon the hydrocolloid into the container, tap the side gently once or twice with the spoon and level off.
6. Weigh the container again and write down the mass of the hydrocolloid.
7. To calculate the density of the hydrocolloid, divide the mass by the volume you obtained for your container. This gives you the density of the hydrocolloid with units g/mL.

Repeat steps 4-7 for each hydrocolloid you have at hand. I would very much appreciate if you email your results directly to me at webmaster (@) khymos (.) org. Please include the volume you measured (larger volume means more accurate measurement) and which brand you used. It will be interesting to see if the brands differ a lot.

I should add one coment about the products from texturePro: this picture indicates that all (?!!) the texturePro hydrocolloids are mixed with maltodextrin (please correct me if I’m wrong - it could be that this only applies to the cocktailPro kit). And I think the same is the case for several of the Sosa products. This increases the volume and eases the use of a measuring spoon (which comes with every texturePro kit), but unless the exact proportion of hydrocolloid to maltodextrin is known, following other recipes than the onces included with the kit is more or less impossible. Let me know if you have further details on the hydrocolloid/maltodextrin ratio in texturePro or Sosa products.

In advance: Thank you very much for your help!

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Ice cubes are used both to cool drinks, but also to significantly impact the flavour of certain drinks. No matter your motivation, you should never use “old” ice cubes which have been sitting in your freezer for a while. Why? Melt some “old” ice cubes and taste the water. You’ll smell why! The reason is that volatile compounds in your freezer slowly find their way into the ice cubes which for some reason mostly are made in trays without a cover. But as I surfed around, researching this post I discovered that oxo and other producers now sell ice cube trays with lids. That’s a small step forward!

Another thing about ice cubes is that they look nice. I admit that air bubbles can sometimes be quite beautiful (and even artistic when pictured with a macro lens as above), but there are times when I whish I could make perfectly clear ice cubes. At room temperature a certain amount of air is dissolved in water. When you cool water, the solubility of air increases (!), but only until the water starts freezing. At this point the water can no longer keep the air dissolved and a bubble is formed. Vice versa - when you boil water the solubility of air decreases and the dissolved gases escape.

When making ice cubes, the bubbles that are formed can easily escape as long as there is no ice blocking their way. This is sort of a catch 22 situation since the air expulsion is directly related to the ice formation. When making ice cubes in a normal freezer, the ice cubes are cooled from the outside, causing the air to get trapped throughout the ice cube.

Many people have thought about smart ways to achieve this (as a quick patent search shows). There are two strategies to obtain clear ice cubes. Let the gas escape while the water freezes or degas and filter the water before freezing. Icicles are a good example that when running water freezes, it normally produces very clear ice. This is utilized in commercial ice cube makers. Here a “cold finger” is exposed to water that moves. This way bubbles are carried away before they can get trapped. These ice cubes typically are ring or cup shaped. The second method is suggested many places on the net. I’ve listed them here together with some thoughts and discussion.

Degassing
Degas the water (i.e. remove the dissolved air). This is easily done by boiling the water for a couple of minutes and letting it cool again. Some webpages suggest that the process should be repeated for best results.

Slow cooling
If the water is cooled too quickly, the ice will not be able to push the impurities ahead of the freezing interface. But if an ice cube freezes from all sides it doesn’t really help as the bubbles get trapped in the middle. A drawback with slow cooling is that the solubility of gas will increase when the water is cooled and so it will allow more gas to dissolve before the water freezes. So slow cooling should probably be combined with some kind of gas tight cover.

Directional cooling
I’ve been pondering about making trays with insulated sides and cover and a metal base, thereby utilizing the fact that metals are superb heat conductors compared to plastic, wood or glass. The metal would then serve to conduct away heat from the water. Bubbles would form on the ice front, but they would probably escape, rather than become encapsuled into the ice. I’ve tried to illustrate it here:

Turns out that someone has actually patented something similar where metal “fingers” are used to conduct away heat from the center, giving ring shaped ice cubes. Does anyone know if these were ever made for sale? Perhaps an ice cube tray in aluminum would work if one insulates the top so that the cubes freeze from the bottom and up, keeping the water on top free flowing so bubbles can escape.

Layer-by-layer method
There might be a simple (but time consuming) way of achieving directional cooling: By building up the ice cubes layer by layer. Once the first layer is frozen this will help freeze the next layer from the bottom up and so on. I guess layers of 1-5 mm would work, but this needs more testing. My experiments so far have not been very promising. Plenty of bubbles, even with a layer of only 2 mm.

Filtering
Particles can act as nucleation sites for air bubbles. To avoid this filter the water and make sure that all the equipment is clean. Also, don’t use a towel to try your equipment as this will probably leave small fibers behind.

Remove salts
Both tap water and bottled water contain trace amounts of salts. When water freezes these minerals are not incorporated into the ice structure. As a consequence the soluble salts will concentrate in the water that’s not yet frozen. In the end there is so little water left that the concentration of the salts becomes sufficiently high so that the freezing point of this remaining water is lower than the temperature in the freezer (meaning that this water won’t freeze). Other salts, especially calcium salts such as calcium carbonate will precipitate. And these particles can act as nucleation sites. If after boiling water there are particles present, these should be filtered away before freezing. The easiest way to get rid of salts is to use distilled water.

I’ve done a couple of experiments and it seems there is no quick fix. The water in the ice cubes pictured above was boiled for several minutes before freezing, but plenty of bubbles formed as you can see. I also tried the layer-by-layer method, but even in a thin layer of only 2-3 mm I could detect many bubbles. So clearly I need to do more experiments.

What are your experiences with making clear ice cubes?

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I recently blogged about the Alinea cookbook, and then in a Q&A with both Grant Achatz and Heston Blumenthal I discovered that there is another great cook book coming up this fall: The Big Fat Duck Cookbook! It’s quite amazing that these two books will be released within weeks of each other this fall.

This is what the publisher promises us:

In the first section of The Big Fat Duck Cookbook, we learn the history of the restaurant, from its humble beginnings to its third Michelin star (the day Heston received the news of this he had been wondering how exactly he would be able to pay his staff that month). Next we meet 50 of his signature recipes – sardine on toast sorbet, salmon poached with liquorice, hot and iced tea, chocolate wine – which, while challenging for anyone not equipped with ice baths, dehydrators, vacuum pumps and nitrogen on tap, will inspire home cooks and chefs alike. Finally, we hear from the experts whose scientific know-how has contributed to Heston’s topsy-turvy world, on subjects as diverse as synaesthesia, creaminess and flavour expectation.

With an introduction by Harold McGee, incredible colour photographs throughout, illustrations by Dave McKean, multiple ribbons, real cloth binding and a gorgeous slip case, The Big Fat Duck Cookbook is not only the nearest thing to an autobiography from the world’s most fascinating chef, but also a stunning, colourful and joyous work of art.

Compared to the Alinea cookbook this one is one is more expensive and has fewer recipes. But hey - who buys cookbooks based on the price/recipe anyway?

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For the following experiment I purposly left some lettuce (Lactuca sativa var. crispa, sold in Norway under the name “Rapid”, it’s a Summer Crisp/Batavian cultivar) to really dry out as you can see from the picture.

After approximately 4 hours in water the leaf looks like this. Notice that along the rim the leaf was so dry that the cells were damaged “beyond repair”.

To illustrate this relatively slow process I set my camera to take a picture every minute and left it for almost 4 hours. I then stiched it together and the resulting time lapse movie shows the process speeded up 720x (click if the embedded video won’t work).

The wonderful thing about this simple experiment is that it actually illustrates the essence of a recently rewarded Nobel prize (and I should thank Erik Fooladi for pointing this out to me)! The 2003 chemistry prize was awarded “for discoveries concerning channels in cell membranes”. The swedish Nobel foundation have excellent pages with further explanations for the public and for specialists alongside an illustrated presentation (recommended!). There are even two animations of which the first is also available on youtube (embedded below, poor resolution, download the original for higher resolution!). It shows how water molecules move through cell membranes:

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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.

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A recent cover feature of Time magazine was “10 Ideas That Are Changing The World”. According to journalist Joel Stein ” ideas are the secret power that this planet runs on”, and guess what? Idea #5 is Kitchen Chemistry. Some are fed up with foams (why does everyone think molecular gastronomy is only about foams anyway?), but my guess is that scientific approaches in the kitchen will become more and more common in the years to come and I certainly welcome this focus on kitchen chemistry.

This paradigm shift won’t be such a big deal in practice. Your oven is pretty much an advanced science gadget already, you use meat thermometers, and that measuring cup looks an awful lot like a beaker. You’re just going to have to step it up a little: replace that liquid-measuring cup with a more accurate dry-weight scale; get a vacuum sealer like that FoodSaver gadget and a Crock-Pot that stays at a precise temperature so you can sous vide meat (which involves cooking it in a bag for a long time in a low-temperature water bath); learn how to use simple chemicals like agar-agar and xanthan gum (just better versions of gelatin and cornstarch, really); review a little high school chemistry. No big deal.

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