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5-Butyl-4-methyloxolan-2-one

By: John Wright
Posted: September 7, 2012, from the September 2012 issue of P&F magazine.

Many years ago, some fortunate soul discovered that storing wine in oak casks not only helped wine withstand hazardous sea voyages—it also added a unique and pleasantly harmonious extra profile to the wine. That novel storage method was later used with spirits, especially whiskey. Today, the vast majority of modern wine and spirits still have a subtle (or not so subtle) addition of oak notes despite the trend of some wines being proudly promoted as “unoaked.”

Oak flavor is complex and is often described in wine writing as “vanilla” or “smoky.” These dominant notes can be very obvious and can often beget complaints that oak has been overdone. However, one of the most interesting and positive components of the complex character of oak is 5-butyl-4-methyloxolan-2-one, commonly referred to as whiskey lactone (FEMA# 3803, CAS# 39212-23-2; F-1). This chemical is basically a derivative of g-octalactone (FEMA# 2796, CAS# 104-50-7) with an added methyl group in the 3 position.

It can exist as a cis or a trans isomer, the cis isomer being of more interest. The character is a highly attractive mélange of creamy, coconut and coumarinic notes. It can function well either as a key component of a range of flavors or as an interesting modifier in a much wider scenario. Still, it’s not an easy ingredient to replace because its character is so complex. g-Octalactone and also g-nonalactone (FEMA# 2781, CAS# 104-61-0) are somewhat similar, but both are much coarser and notably less versatile.

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