Barrel aging cellars

Barrel aging cellars mnst be kept at relatively low temperatnres, with no sndden variations and withont excessive aeration or ventilation. Small cellars may be easier to regnlate. Evaporation from the wine maintains a certain level of hnmidity. Cellars with mold or saltpeter on the walls shonld be avoided, as the evaporation of alcohol fosters these growths, which can harbor an undesirable microbe population. 

After clarification, further modification should be limited. Humidity control is important to regulate water and alcohol loss by avoiding undesirably dry or moist condition in the cellar—low humidity promoting water loss and high humidity favoring alcohol loss through the barrel. Experience has shown that the ideal relative humidity is between 80% and 90%. Clearly, barrel aging is different than that in an inert container of the same size. 

Handle oak barrel aging properly (disinfection, toppings, rackings, cellar temperature)... 

The rhythm of racking must also be taken into account. In a cellar where the barrels are stored with the bung on the side, racking and adjustment of the free SO2 level, accompanied by disinfection of the barrels, must be carried out every 3 months during the first year of barrel aging. If racking is delayed, as shown in Table 8.9, the quantity of free SO2 remaining at the end of the period is too small to protect the wine effectively. The wine is subject to rapid contamination by Brettanomyces yeasts and its ethyl-phenol content inevitably increases. 

Temperatures above 20°C are dangerous during barrel aging. Excessive heat may cause irreversible color breakdown and the formation of tannin polymers that do not always soften the wine. These changes are even more extreme in wines with a low phenol content and in oxidized media. It is always dangerous to barrel-age wines in cellars without temperature control. Furthermore, higher microbial risks are likely to lead to an increase in volatile acidity. 

Diffusion of water, ethanol, and oxygen into and out of barrel-aging wine creates changing environmental conditions which may support or hinder growth of AAB. Depending on the relative humidity (RH) in the cellar, water (at RH <60%) or alcohol (at RH >60%) preferentially is lost... 

Brettanomyces in barrel-aging wines follows a bell-shaped growth pattern, typically reaching maximum population density 5-7 months after vinification. The time frame for development of maximum cell number (and subsequent decline) depends, in large part, on wine chemistry (particularly levels of molecular sulfur dioxide and available fermentable sugars) as well as cellar temperature. Until recently, containment/elimination of Bretta-... 

The appearance of ethyl-phenols dnring aging is mnch more common, especially in used barrels, although phenol off-odors may also develop in red wines aged in new barrels, or even in vats. Fignre 8.10 shows an example of the increase in ethyl-phenol concentrations in a red wine in the barrel dnring the snmmer months. This phenomenon is promoted by the rise in cellar temper-atnre and the decrease in the wine s snlfur dioxide content dnring this period. 

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