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Sour mashing procedures fall into the normal all-grain brewday process between completion of saccharification, and any other desired mashing rests, and separation of the wort from the grain. After the normal saccharification rests and a mashout to 170+ F (76.7+ C) to denature enzymes in the mash, the mash is cooled to approximately 120 F (48.9 C). At this point the mash is more or less pasteurized from the hot temperatures of the mash. In order to reintroduce bacteria into the mash it is inoculated with lactic acid bacteria. This may be accomplished by addition of a pure culture of ''[[Lactobacillus]]'' or, more commonly, by the addition of a small amount of unused malt, which has ''Lactobacillus'' in addition to other bacteria, yeasts, and molds on the husks.
To help favor the growth of ''Lactobacillus'' over the other unwanted microbes, it is important that the mash be kept anaerobic and incubated warm (generally 100ideally 113-120 F120°F/ 37.845-48.9 C9°C) throughout the duration of the sour mash. This can be accomplished by purging the headspace with CO2 (some breweries go so far as to bubble CO2 through their mash while it is cooling, and periodically throughout the souring time) and covering with saran wrap at the liquid-air interface to eliminate air contact. The favoring of ''Lactobacillus'' over spoilage microbes can also be supported by dropping the initial sour mash pH by methods such as the addition of acidulated malt, lactic acid (preferably), or starter wort from a ''Lactobacillus'' culture.
Sour mashing may be conducted on the entire mash, or may be conducted on a portion of the mash. On a homebrew scale, sour mashing only a portion of the grist can easily be accomplished by conducting a small stove top mash before the planned brewday. This pre-soured portion can then be blended in with the wort collected from the normal mash of the remaining grist during the brew day.