A. The heat of the fire expands the air (between the liquid and the cork), and as this air expands, it presses the liquid down, which causes effervescence.
Q. What produces the froth of bottled porter?
A. The carbonic acid gas, produced by its vinous fermentation; which is absorbed by the liquor so long as the bottle is well corked, but is given off in froth as soon as the pressure of the cork is removed.
Q. What gives the pleasant acid taste to soda water, ginger beer, champagne, and cider?
A. The presence of carbonic acid, generated by fermentation, and liberated by effervescence when the pressure of the cork is removed.
Q. Why does fresh spring water sparkle, when poured from one vessel to another?
A. Because fresh spring and pump water contain carbonic acid; and it is the presence of this gas which makes the water sparkle.
Q. What is the fermentation of beer and wine?
A. The production of carbonic acid gas and al’cohol.