Beer Forum

The most traditional Flemish sour ales are Geuze and Kriek. Both of these ales are spontaneously
fermented, which means that no yeast is added by the brewer. But in fact every surface of the brewery is
covered with yeast as are all the fermentation and storage barrels. While many people like the idea that
Geuze can only be produced in Peyottenland because that is where the right yeast live, the truth is that
Brettanomyces was first isolated from English ale and is present in wineries throughout the world. So its
possible to inoculate Flemish sour ales using test tubes of sterile-cultured microorganisms, one after the
other, to rely on the brewery environment itself.

The second lactic fermentation is the staling process that most brewers seek to avoid by heavy hopping.
When the British first built their empire, the shipped beer all the way from Britain to their new colonies. To
protect against this secondary fermentation, they hopped the beer strongly. This is the origin of IPA, India
Pale Ale. At the time, the brewer was seeking the sweet taste of a fresh ale, despite the six month ship-
board aging. With aged hops, the Flemish ale readily undergoes lactic fermentation.

The third Pediococcus\Brettanomyces fermentation is rather interesting. Both bugs are careful, slow, and
very secretive. They can live in the wood used to age the barrels and are never explicitly added to the brew:
they simply persist in the barrel from batch to batch. This fermentation takes half a year. What do the bugs eat? All the simple sugars were eaten by the Saccharomyces and the few that it had trouble with were eaten by the Lactobacillus. The Pediococcus can produce enzymes to convert the complex sugars in the wort to
sugar. The enzyme floats about in the free wort, slowly turning complex sugars to simple sugars. The
Pediococcus has done this to feed itself, but the Brettanomyces goes along for the ride. While the
Pediococcus produces the acidity the Brettanomyces produces the earthiness. Why does this stop at the
end of the year? Not because the complex sugars have run out, but the wort has became so acidic that the
Pediococcus dies and with it the source of the enzyme, which soon decays. Also, the Brettanomyces (and
any residual Saccharomyces) have been eating up any oxygen that diffuses into the fermentation vessel,
typically a large wooden tun. But as the yeast die out, the oxygen level increases, and Pediococcus finds
oxygen toxic.

Left to itself and with a definite but decreasing supply of enzyme and with rising oxygen levels, the
Brettanomyces bravely marches on and is joined by Acetobacter. The former digests what sugars it can and
produces alcohol or acetic acid, depending upon whether there in oxygen present. The latter eats alcohol
and produces acetic acid. As the enzyme supply fails, the Brettanomyces starve to death, leaving only
Acetobacter. It would happily turn everything to malt vinegar if given lots of oxygen, time, and warmth. But
by now the ale is two years old and is ready for bottling.

PhillyBrewer wrote:...Would it speed up the souring process...