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{{Short description|Substance which liberates gas and thereby increases the volume of a dough or batter}}
{{For|the village|Leavening, North Yorkshire}}
{{broader|Bread#Leavening{{!}}Bread leavening}}
{{more citations needed|date=July 2014}}

In [[cooking]], a '''leavening agent''' ({{IPAc-en|ˈ|l|ɛ|v|ən|ɪ|ŋ}}) or '''raising agent''', also called a '''leaven''' ({{IPAc-en|ˈ|l|ɛ|v|ən}}) or '''leavener''', is any one of a number of substances used in [[dough]]s and [[batter (cooking)|batters]] that cause a [[Effervescence|foaming action]] (gas bubbles) that lightens and softens the mixture. An alternative or supplement to leavening agents is mechanical action by which air is incorporated (i.e. [[kneading]]). Leavening agents can be biological or synthetic [[chemical compound]]s. The gas produced is often [[carbon dioxide]], or occasionally [[hydrogen]].<ref>{{Cite book |last=Jacobs |first=Morris Boris |title=The Chemistry and Technology of Food and Food Products |publisher=Interscience Publishers |year=1951 |location=Hoboken, NJ |pages=1932 |language=en}}</ref>

When a dough or batter is mixed, the [[starch]] in the flour and the water in the dough form a [[Matrix (biology)|matrix]]<ref>{{Cite book |last=Hanft |first=Steven L. |title=Fachenglisch für Laborberufe |publisher=John Wiley & Sons |year=2016 |isbn=978-3-527-33512-1 |location=Weinheim |pages=208 |language=en}}</ref> (often supported further by [[protein]]s like [[gluten]] or [[polysaccharides]], such as [[pentosan]]s or [[xanthan gum]]). The starch then [[starch gelatinization|gelatinizes]] and sets, leaving gas bubbles that remain.

== Biological leavening agents ==
* ''[[Saccharomyces cerevisiae]]'' producing [[carbon dioxide]] found in:
** [[baker's yeast]]
** [[Beer barm]] (unpasteurised—live yeast)
** [[ginger beer]]
** [[kefir]]
** [[sourdough|sourdough starter]]
* ''[[Clostridium perfringens]]'' producing [[hydrogen]] found in [[salt-rising bread]]

== Chemical leavening agents ==
Chemical leavens are mixtures or compounds that release gases when they react with each other, with moisture, or with heat.  Most are based on a combination of acid (usually a low molecular weight organic acid) and a [[salt (chemistry)|salt]] of [[bicarbonate]] {{chem|(HCO<sub>3</sub><sup>−</sup>)}}.  After they act, these compounds leave behind a chemical salt.  Chemical leavens are used in [[quick bread]]s and [[cake]]s, as well as [[cookie]]s and numerous other applications where a long biological [[food fermentation|fermentation]] is impractical or undesirable.

===History===
Chemical leavening using [[pearl ash]] as a leavening agent was mentioned by [[Amelia Simmons (author)|Amelia Simmons]] in her ''[[American Cookery]]'',<ref>{{cite book|last=Simmons|first=Amelia|author2=Mary Tolford Wilson|title=The First American Cookbook|edition=1984 reprint|orig-year=1958|year=1984|publisher=Dover|location=Mineola, NY|isbn=0-486-24710-4|url-access=registration|url=https://archive.org/details/firstamericancoo00simm}}</ref> published in 1796.<ref>{{Cite book |last=Smith |first=Andrew F. |url=https://books.google.com/books?id=GZVweuXhZlkC&dq=amelia+simmons+american+cookery+1796+albany+new+york&pg=PT565 |title=The Oxford Companion to American Food and Drink |date=2007-05-01 |publisher=Oxford University Press |isbn=978-0-19-988576-3 |language=en}}</ref>

Since chemical expertise is required to create a functional chemical leaven without producing off-flavors from the chemical precursors involved, such substances are often mixed into premeasured combinations for maximum results. These are generally referred to as [[baking powder]]s.  Sour milk and carbonates were used in the 1800s.  The breakthrough in chemical leavening agents occurred in the 1930s with the introduction of [[monocalcium phosphate]]s {{chem|(Ca(H<sub>2</sub>PO<sub>4</sub>)<sub>2</sub>)}}. Other leavening agents developed include [[sodium aluminium sulfate]] {{chem|(NaAl(SO<sub>4</sub>)<sub>2</sub>·12H<sub>2</sub>O)}}, [[disodium pyrophosphate]] {{chem|(Na<sub>2</sub>H<sub>2</sub>P<sub>2</sub>O<sub>7</sub>)}}, and [[sodium aluminium phosphate]]s {{chem|(NaH<sub>14</sub>Al<sub>3</sub>(PO<sub>4</sub>)<sub>8</sub>·4H<sub>2</sub>O and Na<sub>3</sub>H<sub>15</sub>Al<sub>2</sub>(PO<sub>4</sub>)<sub>8</sub>)}}.  These compounds combine with sodium bicarbonate to give [[carbon dioxide]] in a predictable manner.<ref>John Brodie, John Godber  "Bakery Processes, Chemical Leavening Agents" in Kirk-Othmer Encyclopedia of Chemical Technology 2001, John Wiley & Sons. {{doi|10.1002/0471238961.0308051303082114.a01.pub2}}</ref>

== Other leavens ==
[[Steam]] and [[air]] are used as leavening agents when they expand upon heating.<ref>{{Cite book |last1=Ensminger |first1=Marion Eugene |title=Foods & Nutrition Encyclopedia, Two Volume Set |last2=Ensminger |first2=Audrey H. |publisher=CRC Press |year=1993 |isbn=0-8493-8980-1 |location=Boca Raton, FL |pages=249 |language=en}}</ref> To take advantage of this style of leavening, the baking must be done at high enough temperatures to flash the water to steam, with a batter that is capable of holding the steam in until set. This effect is typically used in products having one large cavity, such as [[popover]]s, [[Yorkshire pudding]]s, [[pita]], and most preparations made from [[choux pastry]]. The effect is also seen to a lesser extent in [[tempura]].

== Mechanical leavening ==
{{Unreferenced section|date=February 2020}}


Using a [[whisk]] on certain liquids, notably [[cream]] or [[egg white]]s, can also create foams through mechanical action. This is the method employed in the making of [[sponge cake]]s, where an egg protein matrix produced by vigorous whipping provides almost all the structure of the finished product.

The [[Chorleywood bread process]] uses a mix of biological and mechanical leavening to produce bread; while it is considered by food processors{{who|date=February 2020}} to be an effective way to deal with the soft wheat flours characteristic of British Isles agriculture, it is controversial{{according to whom|date=February 2020}} due to a perceived lack of quality in the final product. The process has nevertheless been adapted by industrial bakers in other parts of the world.

==See also==
{{Portal|Food}}
* [[Aerated Bread Company]], bakeries started in 1862 in the UK that made carbon dioxide leavened bread 
* [[Baking powder]]
* [[Chametz]]
* [[Parable of the Leaven]]
* [[Passover]]
* [[Unleavened bread]]

== References ==
{{Reflist}}

== Further reading ==
* Matz, S (1972). "Bakery Technology and Engineering", AVI Publishing Co.

== External links ==
{{EB1911 Poster|Leaven}}
* [[Wikibooks]] [[:wikibooks:Cookbook|Cookbook]] has a recipe/module on ''[[:wikibooks:Cookbook:Leavening Agent|Leavening agent]]''

{{Bread}}
{{Authority control}}

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[[Category:Leavening agents| ]]
[[Category:Fermentation in food processing]]