Page 56 - Craft of Whiskey Distilling

AmErICAn DIstIllInG InstItutE | 45
for the spirit into the pores of the oak. In the united States a full-depth charring of barrels (i.e., 1/8 inch) used to age American straight whiskey is predicated by law. This is in spite of the fact that over-charring can actually destroy some of the flavors that are needed to develop the finish of the spirit. This is why toasting, or even a light char, may be a better route, but it is illegal in the united States to age straight whiskies, such as bourbon, in any- thing but fully-charred barrels. A medium-depth char is required just to crack the wood, and a heavier char burns up wood compounds that would only be caramelized by a low- or medium-level char.
Charred barrels produce a deeper colored spirit (temperature is also a contributor) and there is a greater production of esters.
It has been found that the more delicate-flavored spirits like malt whiskey, Canadian whisky, and rum are overpowered by the oak contribution of new charred barrels, so these spirits are aged in once-used bourbon barrels, among other types of used barrels, to give a much more balanced flavor profile.
Toasted oak chips (or staves) can be added to a barrel to provide additional lignin and vanillin, this can augment the aging effect of a barrel. They do provide a significantly differ- ent congener profile than that produced by a once-used charred barrel. And, since putting toasted staves in whiskey barrels is legal in the united States, they are often used by bour- bon distilleries to contribute an additional mellow sweetness to whiskey that would not normally benefit by this as much since the bourbon barrels are fully charred as per uS law.
In summary, a charred barrel contributes color, vanillin, honey, spice, viscosity, and a myriad of other flavors to a whiskey that can be detected by the experienced taster.
ANgELS’ SHARE
As spirits age in barrels, the porosity of the wood results in a certain amount of evapo- ration. In a standard distillery barrel (i.e. 53 gallons) about 10% of the remaining spirit in the barrels evaporates each year. And, it’s not unusual for a barrel of fine 15-year-old single malt Scotch whisky to be less than half full when it’s ready to be bottled.
This loss of spirit due to evaporation is affectionately known as ìthe angels’ shareî. Depending on the temperature and humidity conditions, discussed above, the evaporation will result in an increase in percent alcohol or a decrease. The actual increase or decrease is really a function of more water evaporating than alcohol, or vice versa. For example, high-humidity warehouses result in a decrease in percent alcohol, and lower-humidity ones result in an increase.
SIzE OF bARREL
All of the prior discussion on barrel aging and its associated properties has been based on aging spirits in a standard 53-gallon distillery barrel. For example, a top-quality bour- bon is aged until it’s ìreadyî. Because bourbon, like all American straight whiskies, is aged