Winemaking Wednesday - The Science and Magic of Barrels - Pt. 2

In part 2 of our 3 part series about barrels, Grant explains a bit about the science behind an oak barrel...

Barrel Production and Science

A row of 'barriques'.  More wood contact = more oak flavor.

A row of 'barriques'.  More wood contact = more oak flavor.

Each barrel is shaped, fitted, and toasted by hand over an open flame by an artisan called a ‘cooper’. The result is a liquid tight, savory masterpiece. Since oak wood is porous and breathable, the barrel is not actually ‘air tight’. As a wine ages in barrel, it is exposed to tiny amounts of oxygen that soften the harsh, astringent characteristics of the wine. Over time, tannins mellow and the sharp freshness of young wine eases into a richer, more focused fruit character of a more mature wine.

Barrel aged chardonnay is a perfect example. Chardonnay shows flavors of crisp green apple before barrel aging commences.  After a year in barrel, the wine becomes more like an opulent baked apple pie with cinnamon spice and a decadent creaminess due to malolactic fermentation that takes place in the barrel.  Dark, angular reds also benefit from even more time in the barrel to smooth out their rugged edges and soften the mouth feel of the wine.

In these giant oak vessels in Rioja, Spain, the wine has less contact with the wood, but still matures nicely due to the 'breathability' of oak.

In these giant oak vessels in Rioja, Spain, the wine has less contact with the wood, but still matures nicely due to the 'breathability' of oak.

If a wine is aged too long it is susceptible to oxidation, which in small doses is good and desirable (depending on the style you’re going for), but in large doses is considered a flaw in winemaking.  When picturing over-oxidation, just think about a wine that’s been left uncorked for a week.  Not ideal.  Another danger in the barrel comes from the bacteria acetobacter bacteria, which often present in winemaking, but in large amounts can transform wonderful wines into less wonderful vinegar (or very expensive salad dressing).  

Wines in barrel must continually be monitored and “topped,” or refilled, every month to minimize the head-space in the barrel, reduce risk of oxidation, and to keep acetobacter in check. Minimal amounts of SO2 (or sulfites) are often used to reduce the rate of oxidation and keep wines free of microbial spoilage. 

Next week, we’ll get into a bit more about how winemakers use barrels and develop barrel programs that improve their wines (i.e. the delicious part of the process).  Stay tuned!

- Grant