Editing Milk (section)

==Processing==
[[File:Milkproducts v2.svg|thumb|Milk products and productions relationships (click to enlarge)]]
In most Western countries, centralized dairy facilities process milk and [[dairy product|products obtained from milk]], such as cream, butter, and cheese. In the US, these dairies usually are local companies, while in the [[Southern Hemisphere]] facilities may be run by large multi-national corporations such as [[Fonterra]].

===Pasteurization===
{{Main|Pasteurization#Milk}}

Pasteurization is used to kill harmful [[pathogenic bacteria]] such as ''[[M. paratuberculosis]]'' and ''[[E. coli 0157:H7]]'' by heating the milk for a short time and then immediately cooling it.<ref name="holzinger97">{{cite journal |doi=10.20506/rst.16.2.1037 |title=Milk pasteurisation and safety: A brief history and update |year=1997 |url=https://www.oie.int/doc/ged/d9152.pdf |last1=Holsinger |first1=V.H. |last2=Rajkowski |first2=K.T. |last3=Stabel |first3=J.R. |journal=Revue Scientifique et Technique de l'OIE |volume=16 |issue=2 |pages=441–451 |pmid=9501358 |access-date=January 20, 2021 |archive-date=January 28, 2021 |archive-url=https://web.archive.org/web/20210128060632/https://www.oie.int/doc/ged/d9152.pdf |url-status=live }}</ref> Types of pasteurized milk include full cream, reduced fat, skim milk, calcium enriched, flavored, and UHT.<ref>{{Cite news |url=https://www.betterhealth.vic.gov.au/health/healthyliving/milk |title=Milk |last=Services |first=Department of Health & Human |access-date=October 9, 2016 |archive-url=https://web.archive.org/web/20161010213031/https://www.betterhealth.vic.gov.au/health/healthyliving/milk |archive-date=October 10, 2016 |url-status=live}}</ref> The standard high temperature short time (HTST) process of {{convert|72|°C}} for 15 seconds completely kills pathogenic bacteria in milk,<ref>{{cite journal |doi=10.1021/ie50397a017 |title=Short-Time Pasteurization of Milk |journal=Industrial & Engineering Chemistry |volume=35 |issue=1 |pages=71–84 |year=1943 |last1=Ball |first1=C. Olin}}</ref> rendering it safe to drink for up to three weeks if continually refrigerated.<ref>{{cite journal |doi=10.3168/jds.2009-2144 |pmid=19762797 |title=High temperature, short time pasteurization temperatures inversely affect bacterial numbers during refrigerated storage of pasteurized fluid milk |journal=Journal of Dairy Science |volume=92 |issue=10 |pages=4823–32 |year=2009 |last1=Ranieri |first1=M.L |last2=Huck |first2=J.R |last3=Sonnen |first3=M |last4=Barbano |first4=D.M |last5=Boor |first5=K.J |doi-access=free}}</ref> Dairies print [[best before]] dates on each container, after which stores remove any unsold milk from their shelves.

A side effect of the heating of pasteurization is that some vitamin and mineral content is lost. Soluble calcium and phosphorus decrease by 5%, thiamin and vitamin B12 by 10%, and [[vitamin C]] by 20% or greater (even to complete loss).<ref>{{Cite journal |last=Wilson |first=G.S. |title=The Pasteurization of Milk |journal=British Medical Journal |volume=1 |issue=4286 |year=1943 |pages=261–62 |pmc=2282302 |pmid=20784713 |doi=10.1136/bmj.1.4286.261}}</ref> Because losses are small in comparison to the large amount of the two B-vitamins present, milk continues to provide significant amounts of thiamin and vitamin B12. The loss of vitamin C is not nutritionally significant in a well-balanced diet, as milk is not an important dietary source of vitamin C.

====Filtration====
[[Microfiltration]] is a process that partially replaces pasteurization and produces milk with fewer microorganisms and longer shelf life without a change in the taste of the milk. In this process, cream is separated from the skimmed milk and is pasteurized in the usual way, but the skimmed milk is forced through ceramic microfilters that trap 99.9% of microorganisms in the milk<ref>{{cite book |title=Handbook of Food and Beverage Fermentation Technology |date=2004 |isbn=978-0-203-91355-0 |page=265 |url=https://books.google.com/books?id=PC_O7u1NPZEC&q=Handbook+of+Food+and+Beverage+Fermentation+Technology&pg=PP9 |access-date=September 6, 2016 |last1=Hui |first1=Y.H. |last2=Meunier-Goddik |first2=Lisbeth |last3=Josephsen |first3=Jytte |last4=Nip |first4=Wai-Kit |last5=Stanfield |first5=Peggy S |publisher=CRC Press |archive-date=August 1, 2020 |archive-url=https://web.archive.org/web/20200801132150/https://books.google.com/books?id=PC_O7u1NPZEC |url-status=live }}</ref> (as compared to 99.999% killing of microorganisms in standard [[flash pasteurization|HTST pasteurization]]).<ref>{{cite journal |last1=Stabel |first1=J |last2=Lambertz |first2=A |title=Efficacy of Pasteurization Conditions for the Inactivation of Mycobacterium avium subsp. paratuberculosis in Milk |journal=Journal of Food Protection |date=April 27, 2004 |volume=67 |issue=12 |pages=2719–26 |url=http://naldc.nal.usda.gov/download/40448/PDF |access-date=September 6, 2016 |doi=10.4315/0362-028x-67.12.2719 |pmid=15633677 |archive-url=https://web.archive.org/web/20160920023340/http://naldc.nal.usda.gov/download/40448/PDF |archive-date=September 20, 2016 |url-status=live|doi-access=free }}</ref> The skimmed milk then is recombined with the pasteurized cream to reconstitute the original milk composition.

[[Ultrafiltration]] uses finer filters than microfiltration, which allow lactose and water to pass through while retaining fats, calcium and protein.<ref name=Peterson2015 /> As with microfiltration, the fat may be removed before filtration and added back in afterwards.<ref name=ncse>{{Cite web |url=http://ncseonline.org/nle/crsreports/05jun/97-905.pdf |title=CRS Report for Congress: Agriculture: A Glossary of Terms, Programs, and Laws, 2005 Edition{{nbsp}}– Order Code 97-905 |access-date=July 26, 2009 |archive-url=https://web.archive.org/web/20110810044532/http://ncseonline.org/nle/crsreports/05jun/97-905.pdf |archive-date=August 10, 2011 |url-status=dead }}</ref> [[Ultrafiltered milk]] is used in cheesemaking, since it has reduced volume for a given protein content, and is sold directly to consumers as a higher protein, lower sugar content, and creamier alternative to regular milk.<ref>{{cite news |last1=Eaves |first1=Ali |title=Is This the Best New Post-Workout Drink? |url=https://www.menshealth.com/nutrition/a19540806/is-filtered-milk-better-for-you/|access-date=March 29, 2018 |work=Men's Health |date=August 24, 2015|archive-url=https://web.archive.org/web/20180330013005/https://www.menshealth.com/nutrition/a19540806/is-filtered-milk-better-for-you/|archive-date=March 30, 2018|url-status=live}}</ref>

===Creaming and homogenization===
[[File:Cow milking machine in action DSC04132.jpg|thumb|A milking machine in action]]
Upon standing for 12 to 24 hours, fresh milk has a tendency to separate into a high-fat cream layer on top of a larger, low-fat milk layer. The cream often is sold as a separate product with its own uses. Today the separation of the cream from the milk usually is accomplished rapidly in [[centrifuge|centrifugal]] [[cream separator]]s. The fat globules rise to the top of a container of milk because fat is less dense than water.<ref name="On Food and Cooking"/>

The smaller the globules, the more other molecular-level forces prevent this from happening. The cream rises in cow's milk much more quickly than a simple model would predict: rather than isolated globules, the fat in the milk tends to form into clusters containing about a million globules, held together by a number of minor whey proteins.<ref name="On Food and Cooking"/> These clusters rise faster than individual globules can. The fat globules in milk from goats, sheep, and water buffalo do not form clusters as readily and are smaller to begin with, resulting in a slower separation of cream from these milks.<ref name="On Food and Cooking"/>

Milk often is [[Homogenization (chemistry)|homogenized]], a treatment that prevents a cream layer from separating out of the milk. The milk is pumped at high pressures through very narrow tubes, breaking up the fat globules through [[turbulence]] and [[cavitation]].<ref>{{cite web |last=Goff |first=Douglas |title=Homogenization of Milk and Milk Products |url=http://www.foodsci.uoguelph.ca/dairyedu/homogenization.html |work=Dairy Science and Technology |publisher=University of Guelph |access-date=February 8, 2011 |year=2010 |archive-url=https://web.archive.org/web/20110524061747/http://www.foodsci.uoguelph.ca/dairyedu/homogenization.html |archive-date=May 24, 2011 |url-status=dead}}</ref> A greater number of smaller particles possess more total [[surface area]] than a smaller number of larger ones, and the original fat globule membranes cannot completely cover them. Casein micelles are attracted to the newly exposed fat surfaces.

Nearly one-third of the micelles in the milk end up participating in this new membrane structure. The casein weighs down the globules and interferes with the clustering that accelerated separation. The exposed fat globules are vulnerable to certain enzymes present in milk, which could break down the fats and produce [[rancidification|rancid]] flavors. To prevent this, the enzymes are inactivated by pasteurizing the milk immediately before or during homogenization.

Homogenized milk tastes blander but feels creamier in the mouth than unhomogenized. It is whiter and more resistant to developing off flavors.<ref name="On Food and Cooking"/> Creamline (or cream-top) milk is unhomogenized. It may or may not have been pasteurized. Milk that has undergone high-pressure homogenization, sometimes labeled as "ultra-homogenized", has a longer [[shelf life]] than milk that has undergone ordinary homogenization at lower pressures.<ref>{{cite web |url=https://www.sciencedaily.com/releases/2002/12/021223084204.htm |title=Research Can Lead To Longer Shelf Life For Dairy Products |publisher=Sciencedaily.com |date=December 23, 2002 |access-date=August 28, 2010 |archive-url=https://web.archive.org/web/20100819113427/http://www.sciencedaily.com/releases/2002/12/021223084204.htm |archive-date=August 19, 2010 |url-status=live}}</ref><!--Homogenized milk may be more digestible than unhomogenized milk.<ref name="MichalskiJanuel">{{cite journal |title=Does homogenization affect the human health properties of cow's milk? |doi=10.1016/j.tifs.2006.02.004 |year=2006 |last1=Michalski |first1=Marie-Caroline |last2=Januel |first2=Caroline |journal=Trends in Food Science & Technology |volume=17 |issue=8 |pages=423–37}}</ref>

Kurt A. Oster, M.D., who worked during the 1960s through the 1980s, suggested a link between homogenized milk and [[atherosclerosis]], due to damage to [[plasmalogen]] resulting from the release of bovine [[xanthine oxidase]] (BXO) from the milk fat globular membrane (MFGM) during homogenization. Oster's hypothesis has been widely criticized, however, and has not been generally accepted by the scientific community. No link has been found between atherosclerosis and milk consumption.<ref name="MichalskiJanuel"/>-->

=== UHT ===
[[Ultra-high-temperature processing|Ultra Heat Treatment]] (UHT) is a type of milk processing where all bacteria are destroyed with high heat to extend its shelf life for up to 6 months, as long as the package is not opened. Milk is firstly homogenized and then is heated to 138 degrees Celsius for 2–4{{nbsp}}seconds. The milk is immediately cooled down and packed into a sterile container. As a result of this treatment, all the pathogenic bacteria within the milk are destroyed, unlike when the milk is just pasteurized. The treated milk will keep for up to 6 months if unopened. UHT milk does not need to be refrigerated until the package is opened, which makes it easier to ship and store. However, in this process there is a loss of [[vitamin B1]] and [[vitamin C]], and there is also a slight change in the taste of the milk.<ref>{{Cite news |url=https://www.scientificamerican.com/article/experts-organic-milk-lasts-longer/ |title=Why does organic milk last so much longer than regular milk? |newspaper=Scientific American |access-date=December 1, 2016 |archive-url=https://web.archive.org/web/20161201213111/https://www.scientificamerican.com/article/experts-organic-milk-lasts-longer/ |archive-date=December 1, 2016 |url-status=live}}</ref>