Notes From the Gin Mills: The Science of Booze
In my periodic series on cocktails, I’ve written more about the Manhattan than I have about the martini. In fact, it is from the Manhattan post that the one-off riff on Mirror Spock became the ongoing theme of these posts. In any case, though Manhattans are best made with rye whiskey, pretty much any whiskey is used nowadays, resulting in a wider range of different flavors. On the other hand, gin and/or vodka are the spirits used for martinis, and these vary less in taste than, say, rye, bourbon, and Canadian whiskey. Thus, I have mainly explored the variants of the Manhattan. However, this Christmas past I received a bottle of Bombay Sapphire gin. This inspired some more experimentation with the martini form.
In my mis-spent college days, my bible for liquors and cocktails was The Signet Encyclopedia of Whiskey, Brandy, and All Other Spirits, by E. Frank Henriques. This excellent book is out of print, alas, but still available used. In any case, Henriques argued for economy in buying spirits. According to him, most types of spirit (bourbon, rye, rum, gin, etc.) are, in modern times, much more uniform than people think (or ad departments want us to believe). In blind tastings by non-experts, few can distinguish one bourbon from another, or different brands of gin, and so on. Thus, he argued, the consumer does well to go for the most economical brand. With this in mind, I have almost always bought the least expensive brands of gin and vodka available. However, the aforementioned gift has caused me to change my mind, partially, at least. In order to lay the groundwork for my change of view, I’d like to talk a little about the basics of distilled spirits.
Alcoholic beverages have been known since hunter-gatherer times. If anything containing sugar is acted upon by yeast (or in some cases other microbes), alcohol is produced as a metabolic by-product of the microbes’ consumption of the sugar (carbon dioxide is another by-product, which is why beer is fizzy). This process, of course, is fermentation. By the time of large-scale agriculture, it was possible to manufacture fermented beverages on a large scale, and humans proceeded to do so, using almost anything as a sugar source. Such fermented beverages are classed by base used for fermentation: fruits produce wines, grains produce beer (or sake), agave produces pulque, and so on. Even milk is fermented in some cultures. In any case, in all fermented beverages, the active ingredient, if you will, is the ethyl alcohol (ethanol). The various other chemicals produced by the fermentation process which differentiate beer from wine or pulque or kumyss are known as congeners. These (along with leftover sugar, protein, and other materials from the original base) are what make different alcoholic beverages smell, taste, and look different from each other. They are also believed to be responsible for the different reactions of different people to different alcoholic beverages (e.g. the stories of which beverages you can or can’t mix, or drink in sequence)–the ethanol is identical in all cases.
The fermentation process has limitations, though. Alcohol is a waste product of the microbes that cause fermentation–it is, in fact a toxin (the term intoxication to describe the effects of alcohol is not an accident!). Past a certain point, the microbes are stewing in their own–ahem–excreta, and die off. Thus, fermentation can’t produce much more than 10-15% alcohol by volume (ABV), as is the case in some strong wines. By the late Middle Ages, distillation had been applied to kick up the alcohol content of alcoholic beverages. The principle is simple–ethyl alcohol evaporates at a lower temperature than water (hence the heady sensation of “fumes” if you sniff an alcoholic beverage). By heating a fermented liquid, capturing the steam, and cooling it so that it condenses, one obtains a liquid with a higher alcohol content. Of course, some water also evaporates (distillation alone, in fact, cannot produce a liquid more than 95% alcohol by volume), as do some congeners. This is where things get interesting, and we get to the specifics of gin.
If a beverage is distilled to 160 proof (80 percent ABV–the “proof” rating is always twice the percent of alcohol by volume under U.S. usage), there is still a relatively large content of congeners. Thus, there will be distinct differences of appearance, smell, and taste between different distilled spirits, depending on what they were distilled from, and liquors are so classified. For example, liquors distilled from grain are whiskeys; from wine are brandies; from sugar cane, rum; and so on. Aging in wood barrels further alters taste and appearance, as chemicals leach in from the wood. At some point before bottling, the liquors are diluted to a more drinkable level, typically 40% ABV (80 proof), though 45% (90 proof), 50% (100 proof) and others are sometimes seen.
On the other hand, if a beverage is originally distilled to an original proof of higher than 160 or 170 or so, there are fewer congeners. At a high enough proof–190, or 95%, the maximum obtainable by distillation–there is only alcohol and water left. This produces what is called a rectified or neutral spirit. Such a spirit is colorless, odorless, and tasteless–there is a mouth feel, the typical alcoholic “burn”, but no actual taste. Since congeners are absent, there is no difference between rectified spirits regardless of what they were made from–grain, potatoes, etc. When such plain neutral spirits are diluted back to a more drinkable 40% or 50% ABV, the result is called “vodka”. If it is specifically distilled from grain, it is often labelled “grain neutral spirits”. This, of course, is snob appeal. In the quote from Casino Royale that I gave at the post on martinis linked above, Bond tells the bartender that if he used a vodka distilled from grain, instead of potatoes, the Vesper he’s just ordered would taste even better. This is malarkey–at the proof of original distillation of vodka–remember, a neutral spirit–no congeners that could be detected to differentiate potato vodka from grain vodka are present. James Bond may be a great spy, but he doesn’t understand his chemistry! For anyone who disbelieves: buy a few bottles of potato and grain derived vodkas at similar proofs, and do a blind taste-testing. Let me know how it went after the hangover wears off….
Other neutral spirits are distilled, and then have flavoring added, either by mixture, re-distillation, or a combination of both. The various flavored vodkas now popular are obvious examples. When the flavoring agent is derived from juniper berries, and often other herbal extracts, the result is called gin. Which brings us to the various types thereof–but that’s a topic for next time!