A little more than a week ago Dave Arnold posted a great, new technique: pressure infusion using a conventional iSi whipper! Just think of it – the whipper has been around for decades, and years a go Ferran Adrià pioneered it’s use for espumas. Several have suggested it’s use for carbonation of fruit. But no one had thought of utilizing the whipper for infusions – until August 11th when Dave Arnold of Cooking issues posted the results of his experiments in “Infusion Profusion: Game-Changing Fast ‘N Cheap Technique”. The first blogger to pick up the technique and post about it on August 12th was Linda of playing with fire and water who termed it a revolutionary technique. A couple of days later, on August 17th Aki and Alex of Ideas in food posted a combined pressurized infusion of basil and marination of mozzarella. And then on August 20th James of Jim Seven describes his results comparing conventional cold brewed coffee to cold pressure brewed coffee. It’s really fascinating how fast the idea spread, and it illustrates the benefits of an open and sharing approach to food innovations.

The science behind this is quite simple: in the pressurized canister nitrous oxide (N₂O) dissolves and penetrates the food. When the pressures is suddently released (and it is important to release pressure as fast as possible) the sudden pressure drop causes the dissolved gas to nucleate and form bubbles which expand and disrupt cells, thereby releasing flavor compounds. The physical phenomenon is known as cavitation.

A single N₂O charger contains 8 g of gas corresponding to 0.1818 moles or a volume of 4.1 L at 25 °C and 1 atm pressure. The volume of the chargers is 0.01 L which gives an impressive initial pressure in the chargers of 445 atm! With an approximate volume of 0.7 L the pressure in an empty whipper charged with a single charge would be nearly 6 atm. When liquids are added the volume decreases, but the effect on the head pressure will depend on the type of liquid added. The solubility of N₂O in water is 0.15 g/100 mL at 15 °C, meaning that with 100 mL of water, the head pressure would be roughly 10% higher than in an empty canister (that is, if the solubility is independent of pressure – I’m not quite sure about this). However, since N₂O is a rather non-polar molecule the solubility in ethanol or even oils is much greater than in water, with a resulting lower head pressure. But since flavor delivery is mediated by the dissolved gas suddenly nucleating and bursting cell structures, infusions using ethanol or oil will actually be more effective than those with water because more gas can be dissolved in these solvents (besides the fact that ethanol and oil are better solvents for flavors than water).

Thinking about how I could utilize the pressure infusion technique I came to think about the problems I ran into with hay like off flavors in the parsley and banana flavored marshmallows I made for TGRWT #2. The off flavors can be traced back to 3-methyl-2,4-nonanedione which likely stems from oxidation of unsaturated fatty acids or polyenes. Crushing parsley inevitably leads to oxidation (possibly also enhanced by mixing intra and extra cellular comounds/enzymes), but with pressure infusion – practically in the absence of air – seems to be much gentler than crushing according to Dave’s initial report (as judged by color). So I did a quick experiment with this, infusing a couple of sprigs in 2 dL of water for about 2 minutes. This was by no means enough, and the water had only a faint aroma of parsley (vodka would of course have been much better for the flavor extraction). But it was a clean parsley aroma, and the water was perfectly clear.

I have spent lazy summer days in a “Sommerhus” (e.g. “summer house”) in Denmark with my family and one thing I will share with you is the coffee I enjoyed every morning. My wife doesn’t drink black coffee, so to keep things as simple and easy as possible I brought my Aeropress and a glass of preground coffee (for obvious reasons I decided not to bring my coffee grinder, but I did use a nice coffee from Tim Wendelboe though). At home I have enough equipment to prepare coffee in a dozen ways, but none are as simple and fast as the Aeropress (well – maybe except for Nescafe, but does that count?). I would even dare to say that no other method of preparing coffee offers a better quality-price-convenience ratio!

Although it’s simple, you can still vary grind, amount of water, water temperature and extraction time, so there are plenty of possibilities for experimentation. And believe it or not – there is even an Aeropress world championship. That should give you an idea of how much variation is actually possible!

Using two measuring spoons and the suggested 30-40 second brew time gives a somewhat overdosed and underextracted coffee according to my taste (i.e. a lot of “coffee” aroma, but too little bitterness and a little flat tastewise). This of course also depends a lot on the density of the coffee – and here we’re back to why volume measurements are quite useless for dosing powders. After some experimentation however I’ve ended up with a dose around 15-20 g (ground at setting 40 on my Rancilio Rocky) and extraction times in the range 40-90 seconds. But these conditions are not carved in stone – I keep adjusting them as I get different coffees, and also enjoy how my coffee tastes a bit different every morning. You can get further input on the Aeropress recipes from previous AWC competitors.

Apart from the nice coffee, the best thing about this coffee maker is that it’s very easy to clean. Because of that it’s also the ideal coffee maker to use in the office or at work (in case there’s no good coffee available there). Here are some pictures to illustrate preparation of a cup of coffee and cleaning of the Aeropress:

Areopress upside down on countertop, loaded with coarsly ground coffee (I dialed my Rocky to around 40).

The advantage of the “inverted” method is that no coffee starts to drip before you want it to.

I stir to make sure all the coffee is properly wetted. I then screw on the filter holder with a filter paper inserted (not shown here). Also note that I fill it up all the way with water, and I usually use freshly boiled water. Some prefer to use less water and temperatures anywhere between 75-95 °C.

Oooops – not a perfect fit with the mugs in the summer house, but this did in no way affect the taste of the coffee With the mugs/cups I use at home there’s no problem. After extraction I top of the cup with hot water.

After the filter holder is unscrewed, pressing the plunger the last few millimeters makes the filterpaper and the filtercake pop out of the cylinder. You would of course normally just pop this directly into your waste bin, not on a clean plate as in the picture …

Quickly rinse your Aeropress under running water – and you’re done!

In New York the Experimental Cuisine Collective has been arranging regular seminars since 2007, in Paris Hervé This’ monthly seminar has been running for many years – and now finally the London Gastronomy Seminars are about to launch. To their upcoming event on November 30th they have invited Hervé This, Tony Conigliaro and John Forbes to speak about on Flavor extraction. You might remember that I’ve blogged about the wonders of extraction here previously (focusing on water, ethanol, oil and more specifically on espresso and walnut liqueur) – it’s a really fascinating topic and I wish I could take part in the seminar! If you’re in London or live nearby I would strongly recommend you to visit the seminar

As I mentioned in the post about the exciting color chemistry of nocino I picked some unripe walnuts last year in August when visiting family in Germany. These walnuts were in fact a little to ripe to make nocino from. Preferably the walnuts should be picked end of June when you can still push a knitting pin through the center. Mine were stone hard, but I decided to give it a try anyway, and it shure was worth the bottle of vodka! I checked a couple of recipes and found that many use cinnamon and cloves together with lemon (with peel). I figured I also wanted to try star anise and proceeded with two batches.

Nocino extracted with 45% ethanol
For extraction (> 3 months)
529 g unripe walnuts
385 g 60% ethanol
140 g water

Spices and sugar
4.0 g cinnamon stick
1.2 g star anis
1.2 g cloves
12 g lemon wedge
100 g sugar

Nocino extracted with 60% ethanol
For extraction (> 3 months)
481 g unripe walnuts
436 g 60% ethanol

Spices and sugar
0.8 g star anis
7.8 g cinnamon
12 g lemon wedge
100 g sugar

I covered the walnuts with alcohol in August last year and let them rest for almost 8 months (you can probably do with less, especially if you quarter the walnuts). I then removed the walnuts and added spices, lemon and sugar. After two days I removed the lemon wedge and approximately one month later I filtered off all the spices. As you can see from the pictures below the filter easily clogged. Using normal coffee filters I had to change them roughtly 4-5 times for each batch. I let the filtered nocino rest for some more weeks and then carefully decanted it into a glass bottle, leaving the newly set residue behind. If desired the nocinos can be diluted with water and/or vodka.

Precipitation in nocino extracted with 60% ethanol shown (upper left), filtering was slow (upper right) due to extensive clogging (lower left). A black film had also formed on the inside of the glass.

Nocino tastes marvellous, despite the motor oil like appearance during steeping! The difference between the two ethanol concentrations was less than I had expected. There was significantly more precipitation of black particles with the higher ethanol concentration. Both were however very drinkable! The only thing I might change the next time I attempt this is the amount of spices. I felt that the spices were perhaps a little too dominant and overpowered the walnut flavor, but the flavor was nice anyhow. Since I used walnuts that were a little too ripe it might be that less flavor was extracted, so I assume that my nocino is weaker compared to nocino made with the proper unripe walnuts. This might as well explain why the spices were a little too pronounced.

Update: Reading Elise’s comment below I realized that there was one thing I forgot to mention. Since the walnuts were picked late I could neither cut them in half nor pierce them. After extraction I tried to cut a little into the soft shell under which the black walnut shell is barely visible.

I’ve seen a recommendation to try nocino with strong cheese whereas others prefer it over vanilla ice cream. I’ve also come across two recipes for nocino ice cream so it’s a quite versatile liqueur!

Last year, while visiting family in Germany, I decided to pick some walnuts to bring home to Norway. They were not ripe, which was good, because I was planning to make nocino, a walnut liqueur. You can easily find a number of recipes by googling and there is also a nocino-thread over at eGullet.

What fascinated me the first time a saw nocino mentioned in a book about liqueurs was the nearly black color. Many recipes comment that after steeping, the liquid looks more like used motor oil than something edible. The color is really amazing and I also observed that most recipes recommended the use of gloves as the stains from the unripe walnuts would not easily come off. The juice from the walnuts is a light yellow green color to start with, but when exposed to air it quickly turns dark brown. Color chemistry is always fascinating and I couldn’t resist the temptation to investigate this further.

This picture was taken only 3 days after I steeped the walnuts in ethanol.

I did a little research and found a number of scientific papers about nocino. Some of them focus on the high content of phenolic compounds and possible health effects. Personally I can’t really see how nocino will ever become a significant source of phenolics in anyones diet. Even the article entitled “Influence of processing variables on some characteristics of nocino liqueur” is mainly concerned with how the process variables affect the antioxidant activity. There is no mention of taste or aroma (and this is perhaps why I would not classify these papers as molecular gastronomy), but the authors conlcude that walnuts picked earlier (more unripe) combined with a long steeping time (3 months) give a higher content of phenolics. They correlate the phenolic content to a measure of firmness, but for those making nocino at home an easy way to test the walnuts is to pierce them with a knitting pin – the walnut should be soft all the way through. As a side note I should mention that the walnuts I used were picked in August which is way too late – the inner walnut shell was stone hard, but I decided to give it a try anyway (more on how it all worked out in a comming follow-up post). The closest I came to some input regarding aroma was an article were 12 different phenolic compounds were analyzed in walnut extracts made with 40, 60 and 96% ethanol. Although the total phenolic content was highest when using 96% ethanol, they found that the concentration of some phenolics (protocatechuic, sinapic and p-coumaric acid) increased with the concentration of the ethanol used for extraction, whereas other phenolics (gallic, chlorogenic, vanillic and syringic acid, (+)-catechin, juglone) were best extracted with 40% ethanol. Polyphenolic compounds are normally bitter or astringent. The low molecular weight compounds are typically more bitter. With increasing molecular weight bitterness decreases whereas astringency generally increases. The solubility in water decreases with higher molecular weight. As I mentioned in a previous post on ethanol extractions this is the reason why 30-60% ethanol is most commonly used for infusions and extractions.

Even though the contents of the jar seems to be black, it’s actually still a bright green color if you shine enough light through it. The reason for this is that the jar was kept well closed. Once the nocino is filtered and thereby exposed to plenty of air the color will change to dark orange brown.

Despite all the papers on nocino I still didn’t know more about the colors of nocino, and what I was really searching for was an account of the color changes I observed. The incredible staining of skin and the change from bright green to dark brown and nearly black upon contact with air. Back in 1856 Reischauer and Vogel [1] studied and isolated a compound they named juglone after the latin name of walnut (juglans). In 1885 the structure was elucidated by Bernthsen and Semper who two years later also synthesized the compound [2]. Later Mylius [3] isolated a precursor to juglone, α-hydrojuglone, which upon oxidation yields juglone. And in 1950 Daglish [4] showed that what had become known as “apparent vitamin C” was in fact a hydrojuglone glucoside, a precursor to α-hydrojuglone. This is a nice illustration of how the most stable molecules are discovered first, before one realizes that there are more reactive precursors.

It’s also interesting to note that the structure of juglone is closely related to lawsone, a compound found in the henna plant (Lawsonia inermis) which is used for skin coloring. The hydroxyl group on the quinoid double bond causes lawsone to easily undergo oxidative dimerization (which I belive leads to compounds with a darker color – this would explain why henna color typically needs some time to develop). In the henna plant lawsone exists as a glucoside, and I would suspect that it is in the form of hydrolawsone glucoside which looses glucose and is oxidized as is the case with hydrojuglone.

Read on: Nocino – walnut liqueur (part II) – includes recipes!

References:
[1] Vogel, Reischauer Jahresberichte 1856, 693.
[2] Bernthsen, Semper Berichte der Deutschen Chemischen Gesellschaft, 1885, 18, 203. Bernthsen, Semper Berichte der Deutschen Chemischen Gesellschaft, 1887, 20, 934.
[3] Mylius, F. Berichte der Deutschen Chemischen Gesellschaft 1885, 17, 2411. Mylius, F. Berichte der Deutschen Chemischen Gesellschaft 1885, 18, 463.
[4] Daglish C. Biochem J. 1950, 47, 452. Daglish C. Biochem J. 1950, 47, 458. Daglish C. Biochem J. 1950, 47, 462.

I have recently come to know Miss Silvia. She’s from Italy, weighs a good 14 kg and even my wife welcomed her in our kitchen! As home brew espresso afficionados will know by know, I’ve become the proud owner of an espresso machine from Rancilio! She’s been around for a number of years, and is one of the most popular among prosumer espresso machines available before you take the step up to double boiler machines that allow simultaneous brewing and steaming. Every place that is (proud of) serving espresso uses these machines, but their price is well beyond most coffee lovers budget. The good news however is that even single boiler machines can produce excellent espresso!

The first time I offered the science of espresso any thought was when reading Jeffry Steingarten’s accounts of his espresso adventure (in “It must’ve been something I ate”) which brought him all the way to Italy and Illy and then back again to Manhatten where he set up 14 home espresso machines in his kitchen. This is also where I first was made aware of the fact that 7 g of coffee should be used for a single espresso (which is considerably more than the 5-6 grams found in the Nespresso capsules).

Since I decided to buy an espresso machine I have been devouring sites written by and for coffee enthusiasts: CoffeeGeek, Home Barista and Espresso! My Espresso! to mention a few. You’ll be surprised how much one can possibly write about espresso!

Considering the fact that there is a world championship for baristas, it might seem boisterous to claim that I have pulled a couple of decent espresso shots in the last few weeks. They certainly vary in quality, but by preparing and drinking espressos daily I learn more and more as I taste my way through different types of coffee. One thing I feel quite confident of is that preparing an espresso is the the most sophisticated extraction done in any kitchen. Consider these parameters:

coffee beans
roasting
grinding
dosing
tamping
water pressure
water temperature
extraction time
extraction volume

Luckily all of this has been researched in great detail and the last five generally should not be varied at all. To brew a perfect double espresso you should use water at 92-94 °C and a pressure of 9 bar. During an extraction time of 25-27 seconds you should get 60 mL of espresso – no more, no less! To provide enough back pressure you need to tamp the ground coffee relatively hard in the filterbasket. A pressure of 10-15 kg is recommended. As you can see all these parameters are fixed. So the only things left for the barista to vary is the grinding, the dose and of course the choice of coffee beans (including roasting). Since the recommended amount of coffe for a double espresso is 14-16 grams (some extend the range to 12-18 g), you’re basically left with grinding and the choice of coffee beans. Sounds simple, but there’s a lot that can go wrong. I’ll come back to all of this in part II. The espresso should neither be too bitter nor too acidic. And it should have a nice and stable crema.

“Crema, the dense, reddish-brown foam that tops an espresso, is composed mainly of tiny carbon dioxide and water vapor bubbles surrounded by surfactant films. The crema also includes emulsified oils containing key aromatic compounds and dark fragments of the coffee bean cell structure.”

There is one family whose name is forever linked to espresso – the Illy’s. The above quote is from Ernesto Illy’s article “The complexity of Coffee” which appeared in Scientific American, June 2002 (previously available from illyusa.com, now available through the internet archive – it’s highly recommended!).

The illy company was founded by Francesco Illy (1892–1956) in 1933. In 1935 he invented the precursor to espresso machines as we know them today. His son Ernesto Illy (1925-2008) studied food chemistry and worked with illy for his entire career. Francesco’s grandson Andrea Illy (1964-), also a chemist by training, currently acts as chairman of the board. “Espresso is a miracle of chemistry in a cup,” says Andrea Illy (this is as close to pure molecular gastronomy as you will ever get!). The (scientifically) interested reader will probably enjoy the definitive textbook on the subject: “Espresso Coffee: The science of Quality” which Andrea Illy has co-edited. The more artistically minded might prefer “Illy Collection: A Decade of Artist Cups”.

Further reading, listening and viewing
“Discovering La Dolce Vita in a Cup” (NY Times interview with Ernesto Illy from 2001). There is also a video interview with Ernesto Illy available on DVD, “The Complete Dr. Illy Milan Interview”.

Andrea Illy talked about “The Science of Coffee” at the New York Academy of Sciences (podcast) and was also interviewed by CoffeeGeek.

When it comes to preparation of espresso (which I will digg into in part II), “Espresso Coffee: Professional Techniques” by David C. Schomer is the standard textbook most people refer to, in addition to the videos “Caffe Latte Art” and “Techniques of the Barista”. Schomer developed Espresso Vivace with Geneva Sullivan and operates espresso bars in Seattle. The homepage features an extensive archive with articles on espresso by David C. Schomer.

Previous posts in the extraction series: water, ethanol and oil.

Oils and fats are long molecules which are mainly non-polar and hence the opposite of water which is a polar molecule. Ethanol which has both a polar and a non-polar end falls in between oil and water. I’ve covered extractions using water and ethanol previously. That water and oil are opposites is easily observed by the fact that they don’t mix, and because of it’s lower density oil floats on top of water. This property allows us to easily separate water and oil.

Volatile molecules – the molecules that we detect by their smell – are mainly non-polar and therefore soluble in oil. This is one reason why foods with fat often have a different and often better flavor compared with their fat-free counterparts (fat of course also influences mouth feel etc.). Everytime you cook with oil it will actually help extract aroma (or smell flavorants) from the food ingredients and deliver these to your nose.

There are several oil extracts used in the kitchen, and the nice thing about them is that the oil extracts aromas and then protects them from the air. This is good as it prevents oxidation of the aroma molecules, but in some extreme cases bad because the anaerobic conditions may promote growth of botulinum spores – more on that in the last paragraph. When the flavored oil is added to a dish you get can immediately perceive the aroma. If the oil is tasted pure it serves as a carrier for the aroma giving a small explosion in the mouth (or nose to be more precise…). Some examples I can think of where the oil plays an important role in extracting and delivering aromas are: pesto, tapenade, mayonaise, aioli, curry paste (and all other spice pastes), chili oil and truffle oil to mention a few. Notice that in most of these the source of the aromas is still present in the oil.

One significant addition to the aroma molecules is capsaicin which gives chiles their pungency. Capsaicin is not particularily volatile so it never reaches your nose, but it certainly does burn your tongue! The funny thing is that the receptor being attacked by capsaicin is a protein which is also sensitive to temperature. So when talking about “hot” food it’s true in a double sense. There is an overlap in how our brain perceives food which has a high temperature and food which is spicy.

The fact that water and oil are non-miscible can be utilized in the kitchen. Oil can be used to extract non-polar compounds from a water phase, and oppositely water can be used to extract polar compounds from an oil phase. In the organic chemistry lab water and oil would be separated with a separatory funnel, but in the kitchen a normal plastic bag will work fine. Check out the pictures and description of how a plastic bag is used to clarify butter over at Cooking for Engineers.

Although most of the aroma molecules will be present in the oil, a tiny amount will remain in the water. It is possible to measure how molecules partition between oil and water, and instead of cooking oil one uses octanol. You can read more about the partition coefficient K_{octanol/water} over at Cumbrian food lab.

To start experimenting with this in the kitchen I suggest you start with some colored foods. Flavor compounds are normally colorless so it’s hard to see where they end up. One can put up a very general list of compunds responsible for the color of foods:

We can start with blueberries. For the experiment I used a blueberry syrup and mixed it vigorously with oil using an immersion blender. However, when the phases separated the oil was colorless and the waterphase was still blue. The reason for this is that anthocyanins which give blueberries their nice color are water soluble. No matter how much you blend the blueberries with oil the blue color will remain in the water phase.

I should have waited longer to allow the phases to separate properly, but notice the oil clinging to the glass wall in the right picture – it’s totally clear without any traces of blue/purple color.

For our next experiment we will use carrots or carrot juice. Add some oil and mix with an immersion blender to extract the carotene. What you observe now is that the oil phase turns orange/yellow. The reason for this is that the carotenes are oil soluble. If desired one can separate the two phases with a plastic bag as mentioned above.

Extraction of carotene from carrots. Pictures: 1) I finely grated carrots, 2) Blended them with water and filtered of the remains – the water phase was then layered with plain cooking oil 3) Water and oil were mixed with an immersion blender and the phases left to separate, 4) A plastic bag serves as a separatory funnel – cut a small hole to let out the liquid. The water phase turned grey, probably because I left it at room temperature to allow the phases to separate (1-2 days).

Now that the effect has been demonstrated with food colors it’s time to move on to tastes and aromas. The four basic tastes are all soluble in water, whereas the pungency found in chiles for instance is soluble in oil. Aromas or smell flavorants however are primarily soluble in oil. To test this one can take some clear meat stock, add oil and taste the water and the oil phases separately. The water phase will be salty, and also have a little meaty flavor (our nose detects the tiny amounts of oil which remain in the water water phase, even if no oil droplets can be seen – and of course there are also umami flavorants in the water phase). The oil phase will not be salt at all and have a strong meaty aroma.

Even though you seldom will go to the extremes of separating oil and water phases, it can be good to think about where your aromas goes when you cook. And so you won’t forget I rewrote the first few lines of the Shoop Shoop song:

/ D7 – C7 – / D7 – - – /
Can you tell me where the aroma goes
and how it enters into my nose?

/ Am7 D7 Am7 D7 / / G Em7 Am7 D7 / G C D – /
It’s through the oily phase – Oh yeah, into the nose
In the water phase? – Oh, no, that’s just the salts
If you wanna know where the aroma goes
It’s in the grease, that’s where it is

(aroma should be pronounced more like ‘roma when singing)

–

Somes words about safety: When infusing spices, herbs or garlic – think about the fact that you create anaerobic conditions. If pH is above 4.6, the oil is kept at room temperature, and Clostridium botulinum spores are present you might be bad off (botulinum toxin causes botulism). There are sites that cover this in greater detail. Perhaps the easiest way of preventing the growth of botulimum spores is by adjusting the pH with an acid such as phosphoric or citric acid (that would be the pH of any water phase present as they are not soluble in the oil).

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?

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.