So I've been drinking some higher ABV beers recently (8%+ and up), and I've noticed that the highest beers have low carbonation levels. Can someone explain this from a biological/chemical perspective? Alternatively stated, my incorrect intuition would suggest that each sugar molecule would become two ethanol molecules and two CO_2 molecules -- i.e. more booze means more bubbles. But clearly this doesn't match my experience, so can someone set me straight?
Most of the CO2 is vented during fermentation. To reach the proper carbonation, some breweries have a spunding valve on the fermenters. It only takes a little sugar to ferment to hit the desired level for the style. Some beers have sugar added at the end. Some beers are force carbonated with CO2 from tanks, or with recaptured CO2. When the beer is naturally carbonated, at high ABV the yeast may be a little weak. The brewery may have targeted a lower Volume of CO2, as some big styles traditionally have less carbonation.
Most breweries do an unnatural carbonation of their beer. This is especially required if beers are filtered. It usually comes down to what is expected of the beer style wise. A barley wine for example has a traditionally lower level of carbonation than does a saison. As is the case with many other strong beers, lower carbonation usually means the brewery is sticking to style guidelines. Either way though, a lot of breweries do not leave carb levels where fermentation has left them.
