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.

As malt was one of the foods to pair for this month’s TGRWT I decided to do something with beer. I first considered making a beer gel since the Alinea book has a nice recipe (with potassium citrate and kappa carrageenan – I included the recipe in the hydrocolloid recipe collection), but since I didn’t have carrageenan at hand I decided to try a sorbet. A quick search gave me 4 recipes (links in the table below) and in order to compare these I decided to calculate sugar/beer and sugar/liquid ratios as these are quite crucial in order to obtain the desired consistency of a sorbet. The results are shown in the table below.

reference	beer mL	water mL	sugar g	sugar/liquid	sugar/beer
Recipe 1	330	257	340	0.58	1.03
Recipe 2	1360	50	383	0.27	0.28
Recipe 3	310	567*	311*	0.35	1.00
Recipe 4	710	370	335	0.31	0.47

* Recipe 3 uses milk instead of water. There are also 2 oz liquid glucose which I’ve not included since there is no information about the concentration.

I was surprised to find such a great difference between the recipes with regards to sugar and alcohol content. The large ranges for sugar/liquid and sugar/beer ratios (0.27-0.58 and 0.28-1.03 respectively) suggest to me that the recipes are a little arbitrary. Unfortunately I wasn’t able to find tables plotting out the the combined effect of sucrose and alcohol on sorbets – perhaps you know about such a resource? (I tried googling for ethanol, sucrose and freezing point depression without success) In the end I figured recipe 4 seemed most reasonable and scaled it down a little. I had planned on using lemon juice, but there were no lemons left in the fridge so I went with balsamic vinegar instead.

Beer sorbet
150 mL water
140 g sugar
0,85 g gelatin (1/2 sheet, 0,14%)
10 mL balsamic vinegar
300 mL beer (pilsner type, 4.5% alcohol)

Bring water and sugar to boil and stir until sugar has dissolved. Remove from heat, add bloomed gelatin. Add beer and vinegar. Cool and freeze. If freezing without an ice cream maker, mix well once frozen and freeze again. I served it with diced galia melon, marinated in soy sauce and sugar.

Scientific considerations: I intentionally did not boil the beer to avoid oxidation and an sulfurous flavor, and it’s probably also advisable to let the sugar/gelatin mixture cool down before adding the beer. I’m not particularily fond of stale beer, and not heating the beer is a way to avoid this. To reduce syneresis and inhibit formation of large crystals I added a little gelatin to the recipe (locust bean gum or agar/xanthan will also do the trick). The consistency was perhaps a bit too soft, but the following numbers should be a useful guide when adjusting the recipe.

Final sugar concentration: 23%
Final alcohol concentration: 2.25% (vol%)
Final gelatin concentration: 0.14%

Creamy texture after second freezing!

Verdict: The beer sorbet was a pleasant surprise! Very creamy texture, perhaps a little on the soft side, but the gelatin helped maintain structure. The flavor was sweet, savory and acidic at the same time. The melon with soy sauce however was not so great. The leftover beer sorbet will be served with lemon and lime marinated melon in stead of the soy sauce

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?

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

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

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

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

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

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

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

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

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

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