1) Cooking technique 2) Culinary terminology 3) Embittering 4) Losing enthusiasm 5) Spoilage 6) Spoiling 7) The process of becoming sour 8) Turning bad 9) Turning to vinegar 
Souring is a cooking technique that uses exposure to an acid to effect a physical and chemical change in food. This acid can be added explicitly (for example, in the form of vinegar, lemon juice, lime juice, etc.), or can be produced within the food itself by a microbe such as Lactobacillus. Souring is similar to pickling or fermentation, but sour...
• (p. pr. & vb. n.) of Sour • (n.) Any sour apple.
Adding acid to cream to give it a sour taste.
Sour'ing noun (Botany) Any sour apple. 
[n] - the process of becoming sour
noun the process of becoming sour
Change that occurs to wine on prolonged exposure to air. The ethanol in the wine is oxidized by the air (oxygen) to ethanoic acid. It is the presence of the ethanoic (acetic) acid that produces the sour taste: CH3CH2OH(aq) + O2(g) ® CH...