Editing Milk (section)

===Spoilage and fermented milk products===
{{see also|Fermented milk products}}
[[File:Yakult_drink.jpg|thumb|upright|[[Yakult]], a [[probiotic]] milk-like product made by [[Fermentation (food)|fermenting]] a mixture of [[skimmed milk]] with a special strain of the bacterium ''[[Lactobacillus casei]] Shirota'']]
[[File:Kipsigis_Gourd.jpg|thumb|upright|Gourd used by [[Kalenjin people|Kalenjins]] to prepare a local version of fermented milk called ''[[mursik]]''<ref name="Tracing the origin of Mursik">{{cite web |last1=Kibor |first1=Fred |title=Tracing the origin of Mursik |url=http://www.standardmedia.co.ke/lifestyle/article/2000194283/tracing-the-origin-of-mursik |website=The Standard |date=March 9, 2016 |access-date=November 8, 2016 |archive-url=https://web.archive.org/web/20161109022256/http://www.standardmedia.co.ke/lifestyle/article/2000194283/tracing-the-origin-of-mursik |archive-date=November 9, 2016 |url-status=live}}</ref> ]]

When [[raw milk]] is left standing for a while, it turns "[[sour]]". This is the result of [[fermentation (food)|fermentation]], where [[lactic acid bacteria]] ferment the [[lactose]] in the milk into [[lactic acid]]. Prolonged fermentation may render the milk unpleasant to consume. This fermentation process is exploited by the introduction of bacterial cultures (e.g. ''[[Lactobacilli]] sp., [[Streptococcus]] sp., [[Leuconostoc]] sp.'', etc.) to produce a variety of [[fermented milk products]]. The reduced pH from lactic acid accumulation denatures proteins and causes the milk to undergo a variety of different transformations in appearance and texture, ranging from an aggregate to smooth consistency. Some of these products include [[sour cream]], [[yogurt]], cheese, [[buttermilk]], [[viili]], [[kefir]], and [[kumis]]. ''See [[Dairy product]]'' for more information.

[[Pasteurization]] of cow's milk initially destroys any potential pathogens and increases the shelf life,<ref>{{Cite book |title=Culinary nutrition : the science and practice of healthy cooking |last=B. |first=Marcus, Jacqueline |date=2013 |publisher=Elsevier/Academic Press |isbn=978-0-12-391882-6 |location=Amsterdam |oclc=806291270}}</ref><ref>{{Cite book |url=https://books.google.com/books?id=8tlEAgAAQBAJ&q=Pasteurization+of+cow%27s+milk+initially+destroys+any+potential+pathogens+and+increases+the+shelf+life&pg=PA127 |title=Detailed Project Profiles on Dairy & Dairy Products (2nd Edn.) |last=board |first=NPCS |year=2012 |publisher=Niir Project Consultancy Services |isbn=978-93-81039-10-6 |access-date=October 19, 2020 |archive-date=January 25, 2021 |archive-url=https://web.archive.org/web/20210125182629/https://books.google.com/books?id=8tlEAgAAQBAJ&q=Pasteurization+of+cow%27s+milk+initially+destroys+any+potential+pathogens+and+increases+the+shelf+life&pg=PA127 |url-status=live }}</ref> but eventually results in spoilage that makes it unsuitable for consumption. This causes it to assume an [[unpleasant odor]], and the milk is deemed non-consumable due to unpleasant taste and an increased risk of [[food poisoning]]. In raw milk, the presence of lactic acid-producing bacteria, under suitable conditions, ferments the lactose present to lactic acid. The increasing [[acid]]ity in turn prevents the growth of other organisms, or slows their growth significantly. During pasteurization, however, these lactic acid bacteria are mostly destroyed.

In order to prevent spoilage, milk can be kept [[refrigerator|refrigerated]] and stored between {{convert|1|and|4|C}} in [[bulk tank]]s. Most milk is pasteurized by heating briefly and then refrigerated to allow transport from [[factory farming|factory farms]] to local markets. The spoilage of milk can be forestalled by using ultra-high temperature ([[Ultra-high-temperature processing|UHT]]) treatment. Milk so treated can be stored unrefrigerated for several months until opened but has a characteristic "cooked" taste. [[Condensed milk]], made by removing most of the water, can be stored in cans for many years, unrefrigerated, as can [[evaporated milk]].