A. Carbonic acid gas, which (being heavier than common air) settles on the top of the liquor, in the form of scum.
Q. Why does a small piece of raw meat, or a few raisins improve flat beer?
A. 1st—Because they supply it with nitrogen to form it into al’cohol.
2ndly—As the raw meat, &c. putrifies, it gives off carbonic acid gas into the beer, which gives it “life.”
Q. Why is beer flat, if the cask be open too long?
A. Because too much of the carbonic acid gas (produced by fermentation) is suffered to escape.
Q. How is the carbonic acid gas of beer generated?
A. The saccharine (or sugar) of the malt is converted by fermentation into carbonic acid gas and alcohol.
Q. Why does beer turn flat, if the vent peg be left out of the tub?