Editing Custard (section)

== Chemistry ==
Stirred custard is thickened by [[coagulation]] of egg protein, while the same gives baked custard its gel structure. The type of milk used also impacts the result. Most important to a successfully stirred custard is to avoid excessive heat that will cause over-coagulation and [[Syneresis (chemistry)|syneresis]] that will result in a [[curdled]] custard.<ref>{{Cite book |last=Penfield |first=Marjorie P. |url=https://books.google.com/books?id=rlpRi4urAMkC&q=how+does+custard+thicken&pg=PA144 |page=144 |title=Experimental Food Science |date=2 December 2012 |publisher=Academic Press |isbn=9780323140041 |access-date=4 November 2013 }}</ref>

Eggs contain the proteins necessary for the gel structure to form, and emulsifiers to maintain the structure. Egg yolk also contains enzymes like amylase, which can break down added starch.<ref name=":0" /> This enzyme activity contributes to the overall thinning of custard in the mouth. Egg yolk lecithin also helps to maintain the milk-egg interface. The proteins in egg whites are set at {{convert|60|–|80|C|F}}.<ref>{{Cite journal |last1=Kovacs-Nolan |first1=Jennifer |last2=Phillips |first2=Marshall |last3=Mine |first3=Yoshinori |date=2005-11-01 |title=Advances in the Value of Eggs and Egg Components for Human Health |journal=Journal of Agricultural and Food Chemistry |volume=53 |issue=22 |pages=8421–8431 |doi=10.1021/jf050964f |issn=0021-8561 |pmid=16248532}}</ref>

Starch is sometimes added to custard to prevent premature curdling. The starch acts as a heat buffer in the mixture: as they hydrate, they absorb heat and help maintain a constant rate of heat transfer. Starches also make for a smoother texture and thicker mouth feel.<ref name=":0">{{Cite book |last=McGee |first=Harold |title=On Food and Cooking |year=2004 |isbn=978-0-684-18132-5 |page=71 |publisher=Scribner }}</ref>

If the mixture pH is 9 or higher, the gel is too hard; if it is below 5, the gel structure has difficulty forming because [[protonation]] prevents the formation of [[covalent bond]]s.<ref>{{Cite journal |last1=Matringe |first1=E. |last2=Tan Luu |first2=R. Phan |last3=Lorient |first3=D. |date=1999-09-01 |title=Functional Properties of Milk-Egg Mixtures |journal=Journal of Food Science |language=en |volume=64 |issue=5 |pages=787–791 |doi=10.1111/j.1365-2621.1999.tb15912.x |issn=1750-3841}}</ref>