Picture by Michael Murphy (CC-BY-SA)

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.

Extraction of cherries with ~45% ethanol in water

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?

Extraction of peppermint leaves with hot water

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.

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.

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?

Lettuce should be fresh and crisp but upon storage water will eventually evaporate. The pressure inside the cells drops and the leaves shrink and become less appetizing. The simple yet effective remedy is to immerse the lettuce leaves in plain, cold tap water. The water will then diffuse back into the cells again. The process is known as osmosis [wikipedia].

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:

Read about the physics behind the balancing fork trick.

8. Experiment!

Dare to experiment and try new ingredients and procedures. Do control experiments so you can compare results. When evaluating the outcome, be aware that your own opinions will be biased. Have a friend help you perform a blind comparison, or even better a triangle test to evaluate the outcome of your experiments.

In a scientific context, an experiment is a set of actions and observations performed in the context of solving a particular problem, in order to support or falsify a research hypothesis. In a kitchen context, the problem to solve would typically be related to taste, aroma, texture or color. And the required actions and observations would be cooking and eating.

An essential part of the scientific method is that new knowledge is gained when, based previous knowledge, an assumption is made and tested. In the kitchen, this is exactly what you do when you taste your concoctions repeatedly as you cook. And it is also what makes you an experienced cook, because you remember and learn from your previous successes and mistakes. It might sound very complicated, but here’s how it goes:

1) Observation: soup lacks flavor
2) Hypothesis: adding something with flavor might help
3) Experiment: add more spices
4) New observation: soup tastes more (or less)
5) Hypothesis is either supported (or rejected)

Of these steps, I think observation is the easiest. Coming up with a hypothesis however can sometimes be difficult. If you have lumps in your custard or a sauce that’s separating, it isn’t always easy to think of what to do. This is where books on popular food science and molecular gastronomy might help you.

Think outside the cook book! I mentioned in previous post that you should always question authorities and cook books. And even when you have a recipe that works, remember that it’s nothing more than a suggestion. For instance, it can be useful to know when to be sloppy and when to be accurate with measurements. The smaller amount you measure, the greater the precision should be. Let’s consider a hypothetical recipe that calls for 1000 g flour and 1 g of saffron. Whether you use 999 or 1001 g of flour makes no difference, but using 1 or 2 g of saffron will be quite noticable. A good rule of thumb is that you should measure to within +/- 10% of the given amount. But again, don’t follow this blindly. Experience will show when you can be even more sloppy.

Thinking of good experiments to do requires both creativity and experience, and there are many sources of inspiration. The molecular gastronomy movement has come up with a number of books and blogs which point towards new ingredients and procedures. There are several approaches to flavor pairing (i.e. a general one based on experience and a chemical one based on impact odorants). Further more there’s a lot of inspiration to get from regional cooking – also for molecular gastronomists! Lastly, I think considering not only the food but the whole atmosphere and the setting of the meal is important, because our senses are connected!

The best way to judge the outcome of a new procedure or ingredient is to compare it with the original. I’ve previously termed this “parallel cooking”. In scientific contexts it’s very common to do control experiments and I can’t see why this shouldn’t be done in the kitchen routinely. Im convinced that this could have saved us from many kitchen myths!

Once you’ve done your parallel cooking, you have to taste it. If you did the cooking, you’ll probably have an opnion or expectation that the new dish is better or worse than the original. The big problem here is that due to confirmation bias, if you know what you are eating, this will influence your perception of it. Therefore it’s crucial to do a blind tasting (or a double-blind tasting). Have friend help you label each dish with random three digit numbers (to avoid thinking about ranking) and give them to you. If the dishes can easily be recognized due to color, it’s important that the lights are turned down or that you are blindfolded. State which dish you prefer and have your friend reveal the identity of the dishes tasted.

A slightly more sophisticated test is the triangle test which is commonly used in the food industry. The tester is presented with three samples of which two are identical and the task is to pick the odd one out. Using statistics, it’s possible to evaluate the outcome of repeated tests. The number of correct assignments in a number of triangle tests required for you to be 95% sure there is a difference are given in the table below. Read more about simple difference tests here.

Bionomial distribution for a triangle test (p=1/3) at 0.05 probability level. A more extensive table can be found here.

It seems that this would be the ultimate way to determine whether or not there is a difference between pepsi and coke. It’s more than 50 years since the first experiments were conducted. The theory is simple, but in the real world things aren’t always that simple. Read the entertaining story about Fizzy logic.

There are several examples of experimental cooking out on the net, and I thought I’d share some of them with you as this might illustrate my ideas on the subject.

Many cooks have strong opinions about how garlic should be treated. Should it be minced, crushed or microplaned? And does this really influence the taste and aroma? Or does it only affect the degree of extraction and hence the intensity of the flavor? Dominic of Skillet Doux had a excellent post on this subject in 2006, Deconstructing garlic. The task was formulated as follows:

The subject of this experiment is the effect that various methods of breaking down garlic have on its flavor when used to prepare a dish. The hypothesis is that not only does mincing garlic create a different flavor than crushing it, but also that mincing is the preferred method for pasta sauces. Furthermore, the experiment is intended to determine if microplaning garlic achieves a character different from mincing or crushing.

In his conclusion, Dominic writes ” I was surprised to discover that the difference between the minced and crushed garlic sauces was even more significant than I had previously thought”. Check out his post to find out which kind of garlic treatment he prefers for his pasta sauces. As a side comment it can be mentioned that a group of researchers in 2007 studied the effect of cooking on garlics ability to inhibit aggregation of blood platelets. They found that crushing could reduce the loss of activity upon heating. But unfortunately they didn’t report anything about the flavor.

Other food bloggers have also adopted experimental cooking with emphasis on systematic and thorough testing. Examples include Chad’s experiments with gellan, konjac and iota/kappa carrageenans, Michael Chu’s parallell cooking of bacon and his eggplant test and Papin’s comparison of orange juices – to mention but a few! And I shouldn’t forget Dylan Stiles either whom I mentioned in part 5 of this series:

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 preferred 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).

An extreme example of the application of the scientific method to cooking appeared in the news last spring when the recipe for the ultimate bacon buttie was revealed by scientists from Leeds University. Commissioned by Danish Bacon, the study evaluated more than 700 variations of a bacon buttie. They even came up with a “formula” for the perfect bacon buttie and quantified the required crispiness and crunchiness. The news story was picked up by many news agencies, so although it wasn’t necessarily ground breaking science, at least it was clever marketing.

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Check out my previous blogpost for an overview of the 10 tips for practical molecular gastronomy series. The collection of books (favorite, molecular gastronomy, aroma/taste, reference/technique, food chemistry, presentation/photography) and links (webresources, people/chefs/blogs, institutions, articles, audio/video) at khymos.org might also be of interest.

Click here for full size image

7. Question authorities and learn from the experts

A thick, nicely bound cook book with marvelous pictures and a professional layout signals quality and authority. But unfortunately the nice wrapping is no guarantee that the contents is scientifically sound. I would guess that the searing/sealing myth and adding salt to water used to boil vegetables are among the most ubiquitious of the myths. The challenge for everyone is to question the procedures and explanations given in cook books and those that are inherited from your parents and grand parents. Most of them are fine, but some are not. In fact Hervé This has collected more than 20.000 so called “precisions” from French culinary books that he wants to test.

My seventh tip for pursuing molecular gastronomy in your very own kitchen is to question the cook book authorities, but also to learn from the experts in the field. The site Khymos originally started out as a listing of books and web pages that could be useful for anyone interested in molecular gastronomy and popular food science. When giving presentations it was more convenient for me to refer to a webpage than to have people taking notes of all the references. My own collection of books is constantly growing as you can see from the picture (I justed crossed the 100 cm mark), and I am more than happy to share with you my favorite books. Most of what I know about food chemistry and molecular gastronomy is from these books.

Molecular gastronomy should of course never become a theoretical practice only, so remember that “the proof is in the pudding”, as Nicholas Kurti, one of the pioneers of molecular gastronomy often said. Let taste guide your cooking and learn how to conduct simple blind tastings (more on that in part 8). If possible, do an experiment: if there are two or more procedures, follow them and compare the end result.

Despite the many books and articles that have appeared on food chemistry and molecular gastronomy there are still many questions that remain unanswered. Scientifically, molecular gastronomy is tremendously complex. The science of deliciousness lies in the cross section of analytical, biological, inorganic, organic, physical, polymer and surface chemistry. But even though describing and understanding what happes is difficult, everyone is able to judge the end result! This is quite intriguing and because of this it is possible to become an excellent cook – even if you don’t understand the chemistry behind in every detail. This makes me confident that there will always be an “art” and a “love” component in cooking, as Hervé This puts it in his definition of molecular gastronomy.

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Check out my previous blogpost for an overview of the 10 tips for practical molecular gastronomy series. The collection of books (favorite, molecular gastronomy, aroma/taste, reference/technique, food chemistry, presentation/photography) and links (webresources, people/chefs/blogs, institutions, articles, audio/video) at khymos.org might also be of interest.

I blogged about carbonated strawberries some while ago. Those were made using dry ice which unfortunately is not always easy to get hold of. Last week however I bought a iSi Gourmet Whipper – one of those Ferran Adria uses to make foams/espumas. I plan to experiment with that as well, but the first thing I decided to prepare was carbonated fruit. In fact this is a safe way (the only?) to make carbonated fruit at home using a pressurized container.

The instruction booklet which comes with the iSi Gourmet Whipper only mentions cream chargers (filled with N₂O, dinitrogen oxide), whereas soda chargers (filled with CO₂, carbon dioxide) are not mentioned (I guess the opposite is true for the iSi Siphons?). This is quite amazing actually! Luckily however the cream and soda chargers are exactly the same size and both hold 8 g of gas. So it should be possible to make carbonated fruit with any of the iSi whippers (cream, easy, gourmet, dessert, thermo) or siphons available.

Here’s how you proceed:

1. Fill you iSi whipper (or siphon) with fruit, preferably fruit which has a cut, wet surface to allow the carbon dioxide to dissolve in the water/juice.
2. Screw on top securly
3. Charge with one soda charger (two if you have the 1 L whipper)
4. Leave in fridge over night
5. Release pressure with valve (Important!)
6. Unscrew top and serve immediately!
7. Enjoy!

This is what carbonated grapes look like. As you see, I decided to cut the grapes in to halves.


Notice how they sizzle!

A quick recap of the chemistry: cold water dissolves more CO₂ than tempered water, that’s why we leave it in the fridge. Also, remember that it takes some time for the carbon dioxide to dissolve in water, therefore it’s better not to be in a hurry. A quick calculation of the pressures gives the following: Both gases have molecular weights of 44 g/mol, so 8 g of gas corresponds to 0.1818 moles or 4.1 L at 25 °C and 1 atm pressure. The volume of the chargers is 0.01 L which gives an initial pressure in the chargers of impressive 445 atm! With an approximate volume of 0.7 L this gives a pressure (in an empty whipper) of nearly 6 atm – the same as in a bottle of champagne. However once you add water, the equilibriums will change and the pressure in the head space will drop. Anyone who remembers how to calculate the head space pressure at equilibrium if the container is filled with 0.5 L of water and cooled to 4 °C?

I’ve done some googling and there is also some mention of making carbonated fruit with an iSi whipper over at Ideas in food.

(The word play in the title works better for those with a mother tongue where iSi would be pronounced just like “easy”!)

Erich Berghammer, also known as Odo7 [homepage, myspace] is an aroma jockey or AJ for short. He blows scents over his audience with huge fans and has stocked up a pantry with exotic spices, roots, leafs, oils, extracts and herbs. The smells are vaporized using hot water. This video from Roskilde gives you an idea of the set up (but no smells unfortunately).

From what I can see from his webpage Odo7 has been AJ’ing at clubs, parties, concerts, fashion shows, movie theaters and product presentations. But why hasn’t Odo7 been invited to a restaurant yet? Considering the fact that taste (as used in everyday terms) is 20% taste and 80% smell I could imagine some very interesting eating experiences with an AJ present. Think of it as a way of adding aroma to your food!

I wonder what smells you would use with the different dishes? Perhaps recreate the smell of sea for the starters (seafood). Then the smell of pine, moss and wood for the main dish (wild boar, elk or reindeer) and finish up with orange blossom for the dessert (strawberries).

The two last pairings are based on something I recall from the last International workshop on molecular gastronomy in Erice in 2004. Hervé This mentioned that strawberries combined with orange blossom extract, lemon and sugar are reminiscent of wild strawberries! At the same meeting Jack Lang suggested that branches of pine or juniper be placed around the rim of a large serving plate in front of each person. To speed up aroma extraction and vaporization one would pour hot water over the branches and then serve the food (dark meat/wild game) on a smaller plate placed between the branches. This brings us right back to the flavour pairing principle discussed earlier. But now – instead of combining two foods – we can combine a food ingredient or a dish with the appropriate aromas.

Perhaps at a restaurant experience in the not to distant future you could expect not only a waiter and a sommelier to come to your table, but also an aroma jockey!

I should also mention that the idea of using essential oils in cooking explored in great detail in the book “Aroma: The Magic of Essential Oils in Foods and Fragrance”. I justed received a copy and haven’t had much time to look at it. The fact that recipes for food and bath foam can be found on the same page might be disturbing for some, but I like the whole concept – simply because it takes the science of taste, eh.. aroma, seriously!