hist-brewing: Aging of Distilled Spirits

William A. Millett wmillett at fractal.com.br
Wed Dec 15 20:08:32 PST 1999

Dear Hist-brewers,

I found this in the on line Encyclopedia Britannica (www.eb.com - you can
have 30 days free trial period once you subscribe - no affiliation
whatsoever) amd would like to share it with you, once this became a topic
of discussion for some postings already.

*Maturation of distilled spirits*

One method of classifying distilled liquors is as aged or unaged. Vodka,
neutral spirits for use in a variety of products, most gins, and some rums
and brandies are unaged. Aged products are predominantly whiskeys and most
rums and brandies. 

The term age refers to the actual duration of storage, while maturity
expresses the degree to which chemical changes occur during storage. The
maturation of whiskeys falls into two categories, according to whether
storage is in new or reused cooperage. New charred, white-oak containers are
required by law in the United States for the maturation of products to be
called straight bourbon or rye whiskey. These containers, each containing 50
to 55 gallons, are stored in warehouses sometimes having controlled
temperature and humidity. Older warehouses are called rick houses because
the barrels are stored on stationary frames called ricks. In many newer
houses, barrels are stacked on pallets. 

White oak is one of the few woods that can hold liquids while allowing the
process of breathing through the pores of the wood. The pore size of the
wood is such that small molecules such as water move through the wood more
easily than larger molecules such as alcohol. This breathing process is
caused by temperature and humidity differences between the liquid in the
barrel and the air in the warehouse. Charring the wood makes some of the
wood compounds more soluble. As the liquid in the container moves back and
forth through the wood, ingredients are extracted and carried back into the
container's contents. Maturation also results from the contact of oxygen
from the outside air with ingredients in the alcohol mixture. Therefore,
maturation during aging consists of the interaction of the original
compounds of the distillate, of oxidation reactions, and of the extraction
of flavouring compounds from the wood.
These factors must be well balanced in the properly matured product. The
lower the level of the original congeners, the less wood extract required to
achieve a good balance. 

Outside the United States, reused cooperage is common. Since used containers
have already yielded their initial oak extracts, the resulting product is
low in extracted flavouring ingredients, which is desirable in some
beverages. This maturation method, typified by Scotch and Irish whiskeys,
can be carried on in casks holding up to 132 gallons. These casks have
usually had previous use for storage or maturation of other whiskeys or
wines and may be reused for many maturation cycles. Maturation in dry
warehousing increases the alcoholic content of the liquid in the container,
but the more common practice for Scotch and Irish whiskeys of maturation in
high humidity warehouses reduces the alcoholic concentration. 

The maturation procedure for brandies is similar to that of some whiskeys,
but the brandies are usually matured in fairly large casks or oak
containers. Most brandies are matured for three to five years, but some
remain for as long as 20 to 40 years or even longer. 

Rum is usually matured in reused oak containers; high concentrations of oak
extracts are not considered desirable. Normal maturation time is two to
three years, but rum, generally a blended product, may contain a percentage
of older rums. 

Most governments specify storage time for various products. The United
States requires a two-year storage period for most whiskeys but has no
requirement for any pure alcohol or neutral spirits (close to 100 percent
alcohol) added to such whiskeys in the production of blended whiskey. Canada
requires storage of two years for all distilled spirits. Scotland and
England require a three-year storage and Ireland, five years for all
products classified as whiskey; there are no requirements for vodka and gin.

To cite this page: 
"distilled spirit" Encyclopædia Britannica Online. 
[Accessed 14 December 1999]. 

Copyright © 1994-1999 Encyclopædia Britannica, Inc.

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