How much sugar/sweetness do oak barrels add to whiskey?

October 17, 2014 1:54 PM

The other night a friend of mine argued that aging in oak adds a minimal amount of sugar to whiskey: oak's main addition to the end product is flavour, with the majority of the sugar in whiskey being a product of the fermented mash. Is this true? Does the oak have a significant role in the sugariness and/or sweetness of the end product?
posted by wrabbit to Science & Nature (11 answers total)

Sugar turns to alcohol.
posted by laukf at 1:55 PM on October 17, 2014

Oak doesn't add sugar, but compounds that are aromatically associated with sweetness (like caramel and vanilla-type flavors). Any actual sugar is long gone by aging time.
posted by quince at 2:06 PM on October 17, 2014 [5 favorites]

A distilled spirit contains none of the sugar from the original mash. Sugar does not evaporate. It may contain some other sweet tasting molecules, or it may have other things added after distillation for color or flavor, either in the form of the oak barrels or separately.

However I don't believe oak has an appreciable amount of sugar in it. And neither does any normal whiskey.
posted by aubilenon at 2:13 PM on October 17, 2014 [3 favorites]

Best answer: Quince has it. And to clarify, based on some apparent assumptions in your question: whiskey has no sugar in it from any source. The "sugar ... being a product of the fermented mash" is left in the dregs when the whiskey is distilled; the distillate (which, after aging, becomes whiskey) is only ethanol, water, and some trace esters, phenols and higher-order alcohols that came along in the vapor. Oak aging, in turn, adds additional phenols and esters that are characteristic of vanilla, caramel, tobacco, etc., as well as slowly filtering out some of the higher alcohols. The perception of sweetness in whiskey is all due to the presence of these chemicals which are typically associated with sugary things, such as vanilla. (Unless you mix it with coke or something.)

Anyway, sorry if you weren't assuming the presence of sugar in the final whiskey product, but it sounded like you were.
posted by Joey Buttafoucault at 2:15 PM on October 17, 2014 [6 favorites]

Best answer: Sugar turns to alcohol.

Only if there's something to ferment it, and by the time the whiskey is in the oak barrels it's been distilled, which effectively sterilizes it and any yeast which survived distillation or were naturally present in the barrel would be unable to survive the high alcohol content, especially at cask strength. Cask strength is typically 60-65% ethanol, which is more than enough to cause yeast to go dormant if not kill it outright.

However I don't believe oak has an appreciable amount of sugar in it. And neither does any normal whiskey.

Whiskey does contain sugar. For example, the extensive analysis of Shackleton's whiskey found glucose and fructose in concentrations of 206 and 171 mg/L, respectively. Whether that qualifies as "appreciable" or not (that's about .06 teaspoons in a typical 750mL bottle), but it's certainly present in readily measurable quantities.
posted by jedicus at 2:21 PM on October 17, 2014 [1 favorite]

Response by poster: My impression that oak adds sugar to whiskey came from this article. Perhaps it helps: "Exposure to oak improved the final product—coopers use heat to make casks, breaking down structural lignin, cellulose, and hemicellulose into weird, interesting sugars that dissolve into the spirit." The Mystery of the Canadian Whiskey Fungus. Other articles and blog posts I've found mention "wood sugars" from hemicellulose.
posted by wrabbit at 2:25 PM on October 17, 2014

Best answer: Cellulose, which is the major component of wood, is a sugar polymer: the barrel is made of wood which is made of cellulose which is made of sugar. Of course most of the cellulose is intact, but I'm pretty sure some of the cellulose breaks down into sugars during the charring process for making whiskey barrels. I don't know how much. However, even un-charred wood has enough sugar (e.g., cellobiose) to maintain certain species of Brettanomyces yeast.

As pointed out above, the sugars from the mash would not remain following fermentation and distillation.
posted by exogenous at 2:37 PM on October 17, 2014 [2 favorites]

Best answer:

jedicus: Whiskey does contain sugar. For example, the extensive analysis of Shackleton's whiskey found glucose and fructose in concentrations of 206 and 171 mg/L, respectively. Whether that qualifies as "appreciable" or not (that's about .06 teaspoons in a typical 750mL bottle), but it's certainly present in readily measurable quantities.

From here, sugar can be detected at approximately 4,000 ppm. Adding those two sugar concentrations together, 0.377 mg/kg = 377 ppm, too low for human perception by an order of magnitude. So, essentially not appreciable (in the literal sense of appreciating the sweetness).
posted by IAmBroom at 2:42 PM on October 17, 2014 [1 favorite]

Whiskey does contain sugar. For example, the extensive analysis of Shackleton's whiskey found glucose and fructose in concentrations of 206 and 171 mg/L, respectively.

Of course most of the cellulose is intact, but I'm pretty sure some of the cellulose breaks down into sugars during the charring process for making whiskey barrels.

These are good points and I amend my answer accordingly. However, this comes to the equivalent of a few grains of sugar per an entire bottle, and as IAmBroom points out, this is far too little to provide any perceived sweetness in the final product.
posted by Joey Buttafoucault at 2:48 PM on October 17, 2014 [1 favorite]

Yup. As others upthread have pointed out - it's the charred wood that adds the caramel and vanilla notes to whiskey/whisky and other brown liquors. Charring caramelizes sugars present in wood, and makes those flavors more 'available' to the spirit as it ages. Raw wood, especially oak can add some unpleasant notes, due to the lignin and other compounds.
posted by dbmcd at 3:30 PM on October 17, 2014

There are also scotch whiskeys that use oak formerly used in sherry or brandy aging barrels, so they may impart some of that flavor to the whiskey aged in them. It depends on the sherry style, but there can be a caramel or somewhat sweet flavor there.
posted by LionIndex at 5:23 PM on October 17, 2014