Going Sour: Exploring a Different Acidity and its Cocktail Applications

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Vinegar, the fate of alcohol according to Harold McGee¹, is one of the main sources of acidity in the culinary world. Joining the ranks of other fermented food items such as chocolate, cheese or soy sauce, vinegar is produced by a process called acetic acid fermentation or acetification. And while there is still innovation in the whole process of acetification², the history of vinegar goes way back to the ancient Romans and even the Babylonians 4000 BCE¹. To find out if we can do something truly novel with vinegar in the cocktail world we first have to dive deep into the microbial world of acetification.

Acetification Figure #1

For every vinegar, you need alcohol. More precisely, you need the ethanol in alcohol, which is directly converted into acetic acid by specialized microorganisms². More diverse than often given credit for, vinegar is categorized³ into fruit vinegars (wine vinegar, cider vinegar), vegetable vinegars (rice vinegar, tomato vinegar) and animal vinegars (honey vinegar, whey vinegar). In most acetification processes, the alcoholic beverage, most often wine or apple cider, is aerated for the fermentation procedure to supply enough oxygen for the chemical reaction. Depending on factors such as the raw material and your location, the precise microbial species, which performs the fermentation and largely determines the quality of the resulting vinegar², changes. Initially, species of the genus Acetobacter predominate and are only displaced by species of the acid-resistant Gluconacetobacter genus at acetic acid concentrations above 5%^1,2,3. In the end, the acidity of the final product is well above 6%, whereas the alcohol concentration has declined to around 0.5 – 1%. This residual amount of ethanol is needed as it inhibits the final breakdown of acetic acid to carbon dioxide and water by the resident bacterial.

Other factors determining the flavor of the final product next to the microbes and the raw material are, for instance, the timespan of aging and the choice of wood for the barrels (both very important for balsamic vinegar)^4,5. Tannic, astringent compounds such as gallic acid but also flavorful, aromatic aldehydes such as vanillin are released over time by the degradation of the wood⁵. Chemical reactions inside of the barrel, such as the formation of the aromatic ester 2-phenylethyl acetate (presenting a rose-like scent), further add complexity through aging⁴. In malic acid-containing vinegars, such as apple cider vinegar, a process called malolactic fermentation converts much of the tart malic acid into the less acidic lactic acid. During this process, the buttery flavor compound diacetyl is generated^1,6. All in all, an abounding complexity in flavor gives vinegar the upper hand in the acidity cabinet over citrus juice.

And then there is acetic acid itself, the key player in acetification. Acetic acid does not only have a taste but also a very distinct smell¹. Yet it comes in two forms, undissociated and dissociated. The more acidic the vinegar is (especially from different acids) the more undissociated acetic acid is present¹. As you can smell only the undissociated acetic acid, a stronger aroma can be detected from vinegars which are more acidic. Thus, wine vinegars which are rich in tartaric acid will have a stronger acetic acid aroma than, for instance, malt vinegar⁶. Thanks to its chemical nature, acetic acid (and thereby vinegar) can extract aromatic compounds substantially better from herbs and spices than water-based solutions can, making it a prime candidate for infusions¹.

Vinegar, in the form of shrubs, has recently resurfaced in the world of drinks⁷. And rightly so, as it offers a number of benefits over its acidic competitor, citrus juice. In contrast to citrus juice, vinegar is supremely shelf-stable⁷ (thank you acetic acid!) and does not have to be juiced for every cocktail. Additionally, vinegars have a lot more potential for flavor complexity and drinks shaken with vinegar instead of citrus juice remain clear⁸. Acetic acid is also a lot more powerful than citrus juice, which is why Kelley Slagle coined the general rule to add three times less vinegar to drinks than you would for citrus juice⁹. However, until now the main acids used in drinks are citric acid (from citrus fruits), malic acid (limes, apples and grapes) and tartaric acid (vermouth and champagne)⁹. Bartenders all over the world are even experimenting with chemically pure acids, either those mentioned above or others such as succinic acid or lactic acid^10,11. By adding the pure acid to a drink, you are able to control exactly one factor without bringing in all the (potentially unwanted) color, flavor and texture which you would get from, say, a lemon.

The extreme diversity of different vinegars yields ample room for innovation. Naomi Schimek of the Spare Room uses coconut vinegar (yielding a slightly yeasty flavor¹²) for her tiki-inspired shrub¹³; at the Pitt Cue Co in London pickle juice (which contains a lot of vinegar) is used for their cocktail Big Mac ’n’ Rye¹⁴ and Pok Pok’s Alex Mirkin uses honey vinegar for their Pok Pok Ny’s Hunny¹⁵. In principle anything that contains alcohol can be converted into vinegar. This even opens up the possibility to convert spirits such as rum or whiskey into vinegar. Here, the only issue is the high alcohol content which would immediately kill the acetic acid bacteria. Thus, one would either need to dilute the spirit to about 20 proof or cook off the alcohol (for about two hours¹⁶), both with immediate downsides to flavor. With the panoply of vinegars just emerging at the forefront of cocktails, surely many interesting innovations such as rum vinegar or vinegar based on wines made from foraged wild local plants are still to come and enrich life at the bar.

1) https://books.google.ch/books/about/On_Food_and_Cooking.html?id=bKVCtH4AjwgC&redir_esc=y

2) https://www.hindawi.com/journals/tswj/2014/394671/

3) https://link.springer.com/article/10.1007%2Fs00253-015-6659-1

4) http://www.sciencedirect.com/science/article/pii/S0308814608009898?via%3Dihub

5) http://www.sciencedirect.com/science/article/pii/S0308814608000800

6) http://pubs.acs.org/doi/full/10.1021/jf021180u

7) http://www.nytimes.com/2011/10/12/dining/vinegar-cocktails-are-making-the-rounds.html

8) http://thedrinknation.com/articles/read/8002-Mind-the-Shrubs-A-Colonial-Cocktail-Ingredient-Is-Back-in-Vogue

9) https://www.diffordsguide.com/encyclopedia/62/cocktails/vinegar-and-vinegar-in-cocktails

10) http://www.cooksscience.com/articles/story/balance-of-sour/

11) https://books.google.ch/books/about/Liquid_Intelligence.html?id=UrPmngEACAAJ&redir_esc=y

12) https://recipes.howstuffworks.com/how-vinegar-works1.htm
rn13) http://articles.latimes.com/2012/may/26/food/la-fo-shrub-cocktails-20120526