View source for Rennet

{{short description|Enzymes from the stomachs of ruminants, used in cheese production}}
{{for|the apple varieties|Reinette}}
[[File:Clothbound Cheddar - Rennet (4790811140).jpg|thumb|right|Animal rennet to be used in the [[manufacture of cheddar cheese]]]]

'''Rennet''' ({{IPAc-en|ˈ|r|ɛ|n|ᵻ|t}}) is a complex set of [[enzyme]]s produced in the stomachs of [[ruminant]] mammals. [[Chymosin]], its key component, is a [[protease|protease enzyme]] that [[curdling|curdles]] the [[casein]] in milk. In addition to chymosin, rennet contains other enzymes, such as [[pepsin]] and a [[lipase]].

Rennet has traditionally been used to separate milk into solid [[curds]] and liquid [[whey]], used in the production of cheeses. Rennet from calves has become less common for this use, to the point that less than 5% of cheese in the United States is made using animal rennet today.<ref name="vrg">{{cite web |last1=Yacoubou |first1=Jeanne |title=An Update on Rennet |url=https://www.vrg.org/journal/vj2008issue3/2008_issue3_update_renet.php |website=The Vegetarian Resource Group |access-date=2021-12-24}}</ref> Most cheese is now made using [[chymosin]] derived from bacterial sources.

==Molecular action of rennet enzymes==
One of the main actions of rennet is its [[protease]] [[chymosin]] cleaving the kappa [[casein]] chain.<ref>{{Cite web | url=https://www.thecourtyarddairy.co.uk/blog/cheese-musings-and-tips/rennet-in-cheese-the-science-how-rennet-works/ | title=Rennet in cheese - the science: How rennet works| date=2013-06-12}}</ref> [[Casein]] is the main protein of [[Milk#Proteins|milk]]. Cleavage removes the slightly negatively charged [[glycomacropeptide]] (GMP) from the surface of the casein micelle. Because negative charges repel other negative charges, the GMP prevents casein micelles from adhering to each other. With the GMP removed, the casein micelles can begin to cluster and lose their polar charge, causing them to rise out of the polar water molecules and join non-polar milk fat as a portion of the cheese curd. This action is enhanced in the presence of strong ions like those formed from calcium and phosphate. As such, those chemicals are occasionally added to supplement pre-existing quantities in the cheese making process, especially in calcium phosphate-poor goat milk. The solid truncated casein protein network traps other components of milk, such as fats and minerals, to create cheese.{{citation needed|date=July 2023}}

==Extraction of calf rennet==
[[calf (animal)|Calf]] rennet is extracted from the inner [[mucosa]] of the fourth stomach chamber (the [[abomasum]]) of young, nursing calves as part of livestock butchering. These stomachs are a [[byproduct]] of [[veal]] production.<ref>{{Cite book |title=Traditional Cheesemaking Manual |url=https://books.google.com/books?id=mCBrre1_7I4C&pg=PA6 |page=6 |last=O'Connor. |first=C. |publisher=ILRI|isbn=9789290532736 |date=1993-01-01 }}</ref> Rennet extracted from older calves ([[grass-fed]] or [[Grain-fed beef|grain-fed]]) contains less or no [[chymosin]], but a high level of [[pepsin]] and can only be used for special types of milk and cheeses. As each ruminant produces a special kind of rennet to digest the milk of its own species, milk-specific rennets are available, such as kid goat rennet for [[goat's milk]] and lamb rennet for [[sheep's milk]].<ref>{{cite web |last1=Singley |first1=Nora |title=What You Might Not Know: Not All Cheeses Are Vegetarian! |url=https://www.thekitchn.com/a-complete-meal-vegetarian-the-112672 |website=Kitchn |publisher=Kitchn.com |access-date=30 January 2022}}</ref>

=== Traditional method ===
Dried and cleaned stomachs of young calves are sliced into small pieces and then put into salt water or [[whey]], together with some [[vinegar]] or [[wine]] to lower the [[pH]] of the solution. After some time (overnight or several days), the solution is filtered. The crude rennet that remains in the filtered solution can then be used to coagulate milk.  About 1 gram of this solution can normally coagulate 2 to 4 litres of milk.<ref>{{Cite book|url=https://books.google.com/books?id=lM-mtPn9WwoC|title=Brined Cheeses|last=Tamime|first=Adnan Y.|date=2008-04-15|publisher=John Wiley & Sons|isbn=978-1-4051-7164-9|language=en}}</ref>

=== Modern method ===
Deep-frozen stomachs are milled and put into an enzyme-extracting solution. The crude rennet extract is then activated by adding acid; the enzymes in the stomach are produced in an [[Zymogen|inactive form]] and are activated by the [[stomach acid]]. The acid is then [[Neutralization (chemistry)|neutralized]] and the rennet extract is filtered in several stages and concentrated until reaching a typical potency of about 1:15,000; meaning 1&nbsp;g of extract can coagulate 15&nbsp;kg of milk.{{Citation needed|date=July 2019}}

One kilogram of rennet extract has about 0.7&nbsp;g of active enzymes – the rest is water and salt and sometimes [[sodium benzoate]] ([[E211]]),
0.5%–1.0% for preservation. Typically, 1&nbsp;kg of cheese contains about 0.3 mg of rennet enzymes.<ref>{{Cite web|title=Cheese Technology: Lesson 14. CALF RENNET: PREPARATION AND PROPERTIES|url=http://ecoursesonline.iasri.res.in/mod/page/view.php?id=147314|access-date=2021-02-04|website=ecoursesonline.iasri.res.in}}</ref><ref>{{Cite web|date=2017-08-31|title=Hooked on Cheese: Cheese for Vegetarians|url=https://www.thedailymeal.com/eat/hooked-cheese-cheese-vegetarians|access-date=2021-02-04|website=The Daily Meal|language=en}}</ref>

==Alternative sources==
Because of the limited availability of mammalian stomachs for rennet production, cheese makers have sought other ways to coagulate milk since at least [[Ancient Rome|Roman]] times. The many sources of enzymes that can be a substitute for animal rennet range from plants and fungi to microbial sources.<ref name="EFSA">{{Cite web |url=https://www.efsa.europa.eu/en/supporting/pub/en-689 |title=TECHNICAL REPORT OF EFSA: Explanatory Note for the Guidance of the Scientific Panel of Food Contact Materials, Enzymes, Flavourings and Processing Aids (CEF) on the Submission of a Dossier on Food Enzymes: 3.2. Source Materials and Manufacturing Process: Comments/Explanations: Updated on version 2014:EN-579 |publisher=[[European Food Safety Authority]] |access-date=2015-11-11 |date=2014-11-14 }}</ref>  Cheeses produced from any of these varieties of rennet are suitable for [[lacto vegetarianism|lactovegetarians]], as well as those keeping [[Kashrut|Kosher]]. Fermentation-produced [[chymosin]] is used more often in industrial cheesemaking in North America and Europe today because it is less expensive <!-- and of higher quality --> than animal rennet.<ref name="GMO Database">{{cite web|url=http://www.gmo-compass.org/eng/database/enzymes/83.chymosin.html|publisher=GMO Compass|title=Chymosin|access-date=2011-03-03|url-status=dead|archive-url=https://web.archive.org/web/20150326181805/http://www.gmo-compass.org/eng/database/enzymes/83.chymosin.html|archive-date=2015-03-26}}</ref>

=== Vegetable ===

Many plants have coagulating properties.  [[Homer]] suggests in the ''[[Iliad]]'' that the Greeks used an extract of [[ficus|fig]] juice to coagulate milk.<ref>{{cite book
 | author1 = P. F. Fox | author2 = Paul McSweeney | author3 = Timothy M. Cogan | author4 = Timothy P. Guinee
 | year = 2004
 | title = Cheese: Major cheese groups
 | pages = 2
 | publisher = Academic Press
 | isbn = 978-0-12-263652-3
 | url = https://books.google.com/books?id=vz-2Y7npqj0C&q=fig&pg=PA2
 | access-date = 2009-05-06
 }}</ref> Other examples include several species of [[Galium]], [[Caper|dried caper leaves]],<ref>Mike, Tad, "Capers: The Flower Inside", Epikouria Magazine, Fall/Winter 2006</ref> [[Urtica|nettles]], [[thistle]]s, [[Malva|mallow]], ''[[Withania coagulans]]'' (also known as Paneer Booti, Ashwagandh and the Indian Cheesemaker), and [[Glechoma hederacea|ground ivy]].  Some traditional cheese production in the [[Mediterranean]] uses enzymes from thistle or ''[[Cynara]]'' (artichokes and cardoons). Phytic acid, derived from unfermented [[soy]]beans, or fermentation-produced chymosin (FPC) may also be used.{{Citation needed|date=January 2021}}

[[Vegetable]] rennet might be used in the production of [[Kosher foods|kosher]] and [[halal]] cheeses, but nearly all kosher cheeses are produced with either microbial rennet or FPC.{{citation needed|date=January 2013}} <!-- Worldwide, there is no industrial production for vegetable rennet. -->  Commercial so-called vegetable rennets usually contain an extract from the [[Mold (fungus)|mold]] ''[[Rhizomucor miehei]]'' described below.{{Citation needed|date=January 2021}}

=== Microbial ===
Some molds such as ''[[Rhizomucor miehei]]'' are able to produce [[Proteolysis|proteolytic]] enzymes.<ref>{{Cite journal | last1 = Preetha | first1 = S. | last2 = Boopathy | first2 = R. | journal = World Journal of Microbiology and Biotechnology | volume = 13 | issue = 5 | pages = 573 | year = 1997 | doi = 10.1023/A:1018525711573 |title=Purification and characterization of a milk clotting protease from Rhizomucor miehei| s2cid = 85375727 }}</ref> These molds are produced in a [[fermenter]] and then specially concentrated and purified to avoid contamination with unpleasant byproducts of the mold growth.<ref name="Microbial Rennet">{{cite book |last1=K Ruby Blume |title=Everyday Cheesemaking: How to Succeed Making Dairy and Nut Cheese at Home |date=1 July 2014 |publisher=Microscosm Publishing |isbn=978-1-62106-592-0 |page=116 |url=https://books.google.com/books?id=2g94CAAAQBAJ&pg=PA116}}</ref>

The traditional view is that these coagulants result in bitterness and low yield in cheese, especially when aged for a long time. Over the years{{when|date=September 2019}}, microbial coagulants have improved greatly, largely due to the [[characterization (materials science)|characterization]] and purification of secondary enzymes responsible for bitter peptide formation/non-specific proteolytic breakdown in cheese aged for long periods. Consequently, it has become possible to produce several high-quality cheeses with microbial rennet.<ref>{{cite web|url=http://www.bmbtrade.it/img/1421845498_MarzymeTM.pdf|title=Marzyme Microbial Coagulant|website=BMBtrade.it|date=2011|access-date=2017-07-17|archive-date=2016-05-03|archive-url=https://web.archive.org/web/20160503220141/http://bmbtrade.it/img/1421845498_MarzymeTM.pdf|url-status=dead}}</ref>

It is also suitable for the elaboration of [[vegetarian]] cheese, provided no animal-based ingredients are used in its production.<ref>{{Cite web|title=How to Know if Your Cheese Is Vegetarian Friendly|url=https://www.thespruceeats.com/what-is-vegetarian-rennet-591572|access-date=2021-10-23|website=The Spruce Eats|language=en}}</ref>

=== Fermentation-produced chymosin===

Because of the above imperfections of microbial and animal rennets, many producers sought other replacements of rennet. With genetic engineering it became possible to isolate rennet genes from animals and introduce them into certain [[bacteria]], [[fungi]], or [[yeast]]s to make them produce [[recombinant protein|recombinant]] chymosin during fermentation. The genetically modified microorganism is killed after fermentation and chymosin isolated from the fermentation broth, so that the fermentation-produced [[chymosin]] (FPC) used by cheese producers does not contain a GMO or any GMO DNA. FPC is identical to chymosin made by an animal, but is produced in a more efficient way. FPC products have been on the market since 1990 and, because the quantity needed per unit of milk can be standardized, are commercially viable alternatives to crude animal or plant rennets, as well as generally preferred to them in industrial production.<ref name="Law 2010 100–101">{{cite book|last=Law|first=Barry A.|title=Technology of Cheesemaking|year=2010|publisher=WILEY-BLACKWELL|location=UK|isbn=978-1-4051-8298-0|pages=100–101|url=http://eu.wiley.com/WileyCDA/WileyTitle/productCd-1405182989.html|archive-date=2023-12-26|access-date=2012-07-30|archive-url=https://web.archive.org/web/20231226085910/https://eu.wiley.com/WileyCDA/WileyTitle/productCd-1405182989.html|url-status=dead}}</ref>

Originally created by biotechnology company [[Pfizer]], FPC was the first artificially-produced enzyme to be registered and allowed by the [[US Food and Drug Administration]].<ref>{{cite news|title=FDA Approves 1st Genetically Engineered Product for Food|url=https://www.latimes.com/archives/la-xpm-1990-03-24-mn-681-story.html|access-date=1 May 2014|newspaper=[[Los Angeles Times]]|date=24 March 1990}}</ref><ref name=chymosinCase>Staff, National Centre for Biotechnology Education, 2006. [https://archive.today/20121223101343/http://www.ncbe.reading.ac.uk/NCBE/GMFOOD/chymosin.html Case Study: Chymosin]</ref>  In 1999, about 60% of US [[hard cheese]]s were made with FPC,<ref name="USDA">{{cite web |url=https://fpc.state.gov/6176.htm|title=Food Biotechnology in the United States: Science, Regulation, and Issues|publisher=U.S. Department of State|access-date=2006-08-14}}</ref> which thereafter made up to 80% of the global market share for rennet.<ref>E. Johnson, J. A. Lucey (2006) [https://www.ncbi.nlm.nih.gov/pubmed/16537950 Major Technological Advances and Trends in Cheese]  J. Dairy Sci. 89(4): 1174–1178</ref> By 2017, FPC had 90% of the global market share for rennet.<ref name="johnson2017">{{cite journal | last=Johnson | first=M.E. | title=A 100-Year Review: Cheese production and quality | journal=Journal of Dairy Science | volume=100 | issue=12 | year=2017 | issn=0022-0302 | doi=10.3168/jds.2017-12979 | pages=9952–9965|pmid=29153182|url=https://www.journalofdairyscience.org/article/S0022-0302(17)31054-8/fulltext| doi-access=free }}</ref>

The most widely used FPC is produced either by the fungus ''[[Aspergillus niger]]'' and commercialized under the trademark CHY-MAX<ref>{{cite web|url=http://www.chr-hansen.com/products/product-areas/enzymes/our-product-offering.html|title=Enzymes for Cheese|work=Chr-Hansen.com|archive-url=https://web.archive.org/web/20111101092309/http://www.chr-hansen.com/products/product-areas/enzymes/our-product-offering.html|archive-date=2011-11-01|access-date=2012-07-30}}</ref> by the Danish company [[Chr. Hansen]], or produced by ''[[Kluyveromyces lactis]]'' and commercialized under the trademark Maxiren by the Dutch company DSM.<ref>{{cite web |url=http://www.dsm.com/le/en_US/foodspecialties/html/Products_Maxiren.htm |title=DSM Food Specialties — Product Page — Maxiren |website=DSM.com |access-date=2013-01-28 |url-status=dead |archive-url=https://web.archive.org/web/20120106010450/http://www.dsm.com/le/en_US/foodspecialties/html/Products_Maxiren.htm |archive-date=2012-01-06 }}</ref>

FPC is chymosin B, so it is purer than animal rennet, which contains a multitude of proteins. FPC provides several benefits to the cheese producer compared with animal or microbial rennet: higher production yield, better curd texture, and reduced bitterness.<ref name="Law 2010 100–101"/>

Cheeses produced with FPC can be certified kosher<ref>{{cite web|url=http://www.kashrut.com/articles/cheese/|title=Say Cheese!}}</ref><ref name=Chymax>{{cite web|url=https://www.thecheesemaker.com/pdf/Chymosin_Rennet_Specs.pdf|title=Chymax spec sheet}}</ref> and halal,<ref name=Chymax /> and are suitable for vegetarians if no animal-based alimentation was used during the chymosin production in the fermenter.{{Citation needed|date=January 2021}}

== Nonrennet coagulation ==

Many soft cheeses are produced without use of rennet, by coagulating milk with acid, such as [[citric acid]] or [[vinegar]], or the [[lactic acid]] produced by [[soured milk]]. [[Cream cheese]], [[paneer]], [[rubing]], and other [[:Category:Acid-set cheeses|acid-set cheeses]] are traditionally made this way.
The acidification can also come from bacterial fermentation such as in [[cultured milk]].{{Citation needed|date=March 2010}}

[[Vegan cheese|Vegan alternatives to cheese]] are manufactured without using animal milk but instead use soy, wheat, rice or cashew. These can be coagulated with acid using sources such as vinegar or lemon juice.<ref>{{cite web|url=http://www.onegreenplanet.org/vegan-recipe/10-vegan-cheeses-that-will-knock-your-socks-off/|title=These 25 Vegan Cheeses Will Make You Quit Dairy Forever|date=2017-05-19}}</ref><ref>{{cite web|url=http://www.chooseveg.com/11-vegan-cheese-recipes-that-will-change|title=12 Vegan Cheese Recipes That Will Change Your Life|access-date=2016-05-02|archive-date=2017-10-09|archive-url=https://web.archive.org/web/20171009042422/http://www.chooseveg.com/11-vegan-cheese-recipes-that-will-change|url-status=dead}}</ref><ref>{{cite web|url=http://www.veganricha.com/category/cheese|title=Vegan Cheese Recipes}}</ref><ref>{{cite web|url=http://www.vegkitchen.com/recipes/8-amazing-vegan-cheese-recipes/|title=8 Amazing Vegan "Cheese" Recipes|date=12 May 2014}}</ref>

== In mythology ==
In [[Yazidism]], the Earth is believed to have coagulated and formed when rennet flowed from the White Spring of the celestial [[Lalish]] in heaven into the Primeval Ocean.<ref name="Kreyenbroek 2005">{{cite book | last=Kreyenbroek | first=Philip | author-link=Philip G. Kreyenbroek | title=God and Sheikh Adi are perfect: sacred poems and religious narratives from the Yezidi tradition | publisher=Harrassowitz | publication-place=Wiesbaden | year=2005 | isbn=978-3-447-05300-6 | oclc=63127403}}</ref>

==See also==
{{Portal|Biology}}
* [[Cheese]]
* [[Junket (dessert)]]
* [[Milk]]
* [[Pepsin]]

==References==
===Footnotes===
{{Reflist|30em}}

===Bibliography===
{{Refbegin}}
* Carroll, Ricki.  ''Making Cheese, Butter, & Yogurt''. Storey Publishing 2003.
* "Biotechnology and Food: Leader and Participant Guide", publication no. 569, produced by North Central Regional Extension. Printed by Cooperative Extension Publications, University of Wisconsin-Extension, Madison, WI, 1994. Publication date: 1994. Tom Zinnen and Jane Voichick
{{Refend}}

==External links==
* [https://web.archive.org/web/20070526171726/http://biology.clc.uc.edu/fankhauser/Cheese/Rennet/Rennet.html Fankhauser's Page on Rennet history and use]
* [https://onlinelibrary.wiley.com/doi/full/10.2903/j.efsa.2017.466 Appendix D - Assessment of filamentous fungi - Qualified Presumption of Safety]
* [http://www.inchem.org/documents/jecfa/jecmono/v28je08.htm FDA-registration of recombinant chymosin]
* [https://web.archive.org/web/20070307181756/http://dwb.unl.edu/Teacher/NSF/C08/C08Links/www.fst.rdg.ac.uk/courses/fs560/topic1/t1g/t1g.htm Recombinant Chymosin]
* [https://www.journalofdairyscience.org/article/S0022-0302(90)78882-0/abstract Cheese Yield Experiments and Proteolysis by Milk-Clotting Enzymes]
* [https://web.archive.org/web/20110928185203/http://lib.bioinfo.pl/pmid:15969502 Validation of recombinant and bovine chymosin by mass spectrometry]
* [https://doi.org/10.1007%2Fs11947-010-0431-4 Native and Biotechnologically Engineered Plant Proteases with Industrial Applications]

{{Aspartic acid proteases}}
{{Enzymes}}
{{Authority control}}

[[Category:Animal glandular products]]
[[Category:Cattle products]]
[[Category:Dairy industry]]
[[Category:EC 3.4.23]]
[[Category:Cheese coagulants]]