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Aeration. The charging with gas, usually carbon dioxide (q.v.), but also with air, of batters (q.v.), doughs (q.v.), egg whites (q.v.), shortening (q.v.), etc., for the purpose of increasing their volume (q.v.) and producing a light, delicate structure in the final baked product. Aeration may be achieved by biological means, as with yeast fermentation in doughs, by physical means, as with vigorous mixing (q.v.) or whipping (q.v.) that incorporates air into the egg whites and batters, or by chemical means as in the reaction of baking soda (sodium bicarbonate) (q.v.) with leavening acids (q.v.) to produce carbon dioxide gas, or the decomposition of ammonium bicarbonate (q.v.) under the influence of oven heat into ammonia (q.v.), carbon dioxide and water vapor (q.v.).