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Jul 17, 2007 09:43 PM

what makes alcohol smooth?

This may sound like a dumb question, but I'm wondering what happens chemically to alcohol that makes some spirits feel smooth, and others feel rough. Does anyone know the science behind this?


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  1. Adding a bit of sugar, as in the case of most flavored vodkas, some whiskies and various other spirits and liqueurs, will always take the edge and help counter the alcohol 'burn'. Also, some spirits brands, although they would probably never admit to it, use soothers or mellowing flavors. I am not sure as to exactly how these compunds work, but at very low usage levels they can mitigate the harshness of alcohol in certain products. A lot of what they are accomplishing is most likely due to certain receptor sites being blocked on the tongue, as in the case with sugar in spirits.

    1. A lot of the burn in alcohol is from the other chemicals that are in it. When distilling, a lot of these chemicals come off at the beginning of the process, and others at the end. They are known as the 'heads' and 'tails'. Some of the heads and tails also have wanted flavors. The distiller has to know how much of the heads and tails to retain with the body for the best flavor, but also keep out the part that has the rougher, burning tastes and compounds that also can cause hangovers.

      This is the part of the distillation process that is art, not science. It is based on taste and 'feel' or intuition at times, as well as experience with each still; because they all react differently, even if they are the exact same model. This is especially noticeable in alembic or 'pot' stills.

      I have a distiller friend I am visiting today and I will ask him for more detailed info.

      1 Reply
      1. re: JMF

        Thanks. Any info you can provide would be much-appreciated.

      2. it's also a pretty common practice to throw in some glycerin, as it's much cheaper than taking a smaller cut of the distillate and allowing time to mellow it out.

        4 Replies
        1. re: warrenr

          Yes, glycerin is used in some liqueurs to achieve the silky mouthfeel. I have also heard that some of the new 'wet', citrus-style gins are using it for the same purposes, to make there gin more appealing to a crowd that is used to flavored vodkas.

          1. re: Papa Kip Chee

            I'm specifically interested in what happens to the alcohol from aging in wood, or what is achieved through distilling techniques. I'm speaking about high-end whiskeys and cognacs, as an example. That's interesting to know, though, about the glycerine. I wonder why there's no need to disclose that on the label.

            1. re: Josh

              I think that these ingredients at low levels are considered GRAS in the EU, US, and most other countries as natural flavors or ingredients. Also, spirits, being regulated by the TTB for the purpose of tax collection, are not required to have the same labeling as food, and the big spirits companies spend lots of money in the right places making sure it stays that way.

              1. re: Josh

                I've been told that glycerin is actually a natural byproduct of distilling and many spirits have low glycerin levels because of this, so adding more may not need to be disclosed.

          2. There are basically two categories of stills: pot stills, which are also known as alembic stills, and column, fractioning and continuous stills. This second category is more vast and too grand to discuss in short time. Pot stills are what produce scotch malt whisky, irish whiskey, cognac, armagnac, and others, all of which have those smooth characteristics about which you enquire. These products all begin as fermented liquids of relatively low alcohol content. One pass through a pot still roughly doubles the alcohol content (but please bear in mind that there are SO MANY variables in distilling that nothing I say should be taken as a fixed quote) Some spirits stop at one pass(armagnac) while others go two, three, four passes, but rarely more. The pot still is inefficient in achieving high alcohol percentage in the spirits, yet this is the crux of the matter, because several compounds, called many things including congeners and fusel oils, are left in the distillate. Placed in contact with wood and left to age, these compounds go through transformations on their own and in conjunction with chemical structures in the wood. Straight from the still, these compounds can be downright nasty, but given time, up to decades for some cognacs, they develop that smoothness of which you speak. The other category of stills are very good at "stripping" the alcohol out of the fermented liquid and produce that clear, antiseptic smelling, burning juice called grain alcohol. There is just tons of info out there on the subject, but a very enjoyable book on whisky called Peat, Smoke and Spirit by Andrew Jefford might be a place to start.