I don’t know much about brewing, but I’ve been seeing some videos on youtube that have me curious. Apparently “oaky” flavor notes come from oak wood, either in the form of oak wood casks or just little cubes added in. How does the wood not ferment? Because growing up I’ve heard so many horror stories about methanol poisoning and I don’t know how this would work.
In: Biology
The yeast cannot digest the wood materials (cellulose and lignin) any more than you can. That’s why it doesn’t ferment. It’s also why you can just leave cut wood logs out with nothing but a tarp covering them, and they don’t meaningfully break down–most bacteria can’t digest cellulose. Some fungi do, that’s why they grow on fallen, rotting logs, but if you keep the wood dry, the fungus has no water and thus can’t grow.
Instead, the inner layers of the oak barrel (usually one used for aging whiskey, bourbon, or other spirits) can interact with the beer, allowing some of the volatile compounds inside (flavor and odor compounds) to dissolve into the liquid. Sometimes, if oak barrels aren’t available, a brewery might just age the beer with literal oak chips or the like, but this obviously produces inferior results to actually using real barrels.
Further, the alcohol content of the beer genuinely acts as an antimicrobial agent. Ethyl alcohol is toxic to many single-celled lifeforms. Heck, it’s even toxic to yeast; if you somehow manage to reach over 13% alcohol, the yeast will start dying off because the environment is too toxic for them to survive.
Methanol is almost never a real concern if the brewer has properly selected a laboratory-grown, well-understood strain of yeast. Even wild yeast is unlikely to do any kind of fermentation that would contain meaningful amounts of methanol. It’s only when you start doing *distilled* spirits that methanol becomes a concern.
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