Buzz
Why doesn't bread become alcoholic when it uses almost identical ingredients to beer (aside from hops)?
Josh Velson:
All yeast-based breads contain a small amount of alcohol. Have you ever caught the scent of a loaf of bread rising, or noticed the air beneath the dough that's covered as it rises? It gives off a distinctly boozy aroma. And that sweet fragrance fresh bread has, beneath the yeast and the nutty notes from the Maillard reaction? That's alcohol.
However, most of the alcohol in the dough evaporates into the air during baking. This process is similar to how much of the water in the dough disappears. It's well-known that bread contains a small amount of residual alcohol—up to 1.9 percent. Back in the 1920s, the American Chemical Society even had researchers report on it.
On a personal note, I once unintentionally made exceptionally boozy bread by letting white bread dough rise for too long. The result was that not enough alcohol evaporated, and the bread ended up tasting of alcohol. You can also detect alcohol in the underbaked, doughy sections of white bread, which I strongly do not recommend attempting to make.
From an industrial biochemistry perspective, many [people] argue that alcohol is only produced by yeast in a “starvation process” once they run out of oxygen. This is incorrect.
The most common yeasts used in brewing and baking, from the Saccharomyces genus (as well as some Brettanomyces species, which are used in beer production), will begin producing alcohol in both beer wort and bread dough right away, regardless of oxygen availability. This is a surprising finding because it contradicts the most energy-efficient process for the yeast cell (and also the simplified version of yeast biology often taught to home brewers). Typically, it’s expected that the cell will carry out aerobic respiration (converting sugar and oxygen to carbon dioxide and water) until oxygen is depleted, then shift to alcoholic fermentation, which occurs without oxygen but provides less energy.
Instead, if a Saccharomyces yeast is placed in a high-sugar environment, it will start producing ethanol, regardless of the presence of air, diverting sugar into the anaerobic respiration pathway while still running the aerobic process at the same time. This phenomenon is called the Crabtree effect, and it's believed to help suppress competing organisms in high-sugar environments, since ethanol has antiseptic properties that yeasts can tolerate but their competitors cannot. It’s a quirky aspect of Saccharomyces biology that you mostly learn about only if you’ve spent too much time cultivating yeast cells… like I have.
This article was first published on Quora. Click here to read more.
