Custard is a variety of culinary preparations based on sweetenedmilk,cheese, orcream cooked withegg oregg yolk to thicken it, and sometimes alsoflour,corn starch, orgelatin. Depending on the recipe, custard may vary in consistency from a thin pouring sauce (crème anglaise) to the thick pastry cream (crème pâtissière) used to filléclairs. The most common custards are used incustard desserts ordessert sauces and typically include sugar and vanilla; however,savory custards are also found, e.g., inquiche.
Preparation
Custard is usually cooked in a double boiler (bain-marie), or heated very gently in asaucepan on a stove, though custard can also be steamed, baked in the oven with or without awater bath, or even cooked in apressure cooker. Custard preparation is a delicate operation because atemperature increase of 3–6 °C (5.4–10.8 °F) leads to overcooking andcurdling. Generally, a fully cooked custard should not exceed 80 °C (176 °F); it begins setting at 70 °C (158 °F).[1] Abain marie water bath slows heat transfer and makes it easier to remove the custard from the oven before it curdles.[2] Adding a small amount of cornflour (U.S.corn starch) to the egg-sugar mixture stabilises the resulting custard, allowing it to be cooked in a single pan as well as in a double-boiler. Asous-vide water bath may be used to precisely control temperature.
A formal custard preparation, garnished with raspberries
While custard may refer to a wide variety of thickened dishes, technically (and inFrench cookery) the wordcustard (crème or more preciselycrème moulée,[kʁɛmmule]) refers only to an egg-thickened custard.
Whenstarch is added, the result is called 'pastry cream' (French:crème pâtissière,pronounced[kʁɛmpɑtisjɛːʁ]) or confectioners' custard, made with a combination of milk or cream, egg yolks, fine sugar, flour or some other starch, and usually a flavoring such as vanilla, chocolate, or lemon.Crème pâtissière is a key ingredient in many French desserts, includingmille-feuille (or Napoleons) and filled tarts. It is also used in Italian pastry and sometimes inBoston cream pie. The thickening of the custard is caused by the combination of egg and starch.Corn flour or flour thickens at 100 °C (212 °F) and as such many recipes instruct the pastry cream to be boiled. In a traditional custard such as acrème anglaise, where eggs are used alone as a thickener, boiling results in the over-cooking and subsequent curdling of the custard; however, in a pastry cream, starch prevents this. Once cooled, the amount of starch in pastry cream sets the cream and requires it to be beaten or whipped before use.
Whengelatin is added, it is known ascrème anglaise collée ([kʁɛmɑ̃ɡlɛzkɔle]). When gelatin is added andwhipped cream is folded in, and it sets in a mold, it isbavarois. When starch is used alone as a thickener (without eggs), the result is ablancmange.
In the United Kingdom, custard has various traditional recipes some thickened principally with cornflour (cornstarch) rather than the egg component, others involving regular flour; seecustard powder.
After the custard has thickened, it may be mixed with other ingredients: mixed with stiffly beaten egg whites and gelatin, it ischiboust cream; mixed with whipped cream, it iscrème légère,[kʁɛmleʒɛːʁ]. Beating in softened butter producesGerman buttercream orcrème mousseline.
A quiche is a savoury custard tart. Some kinds oftimbale or vegetable loaf are made of a custard base mixed with chopped savoury ingredients.Custard royale is a thick custard cut into decorative shapes and used to garnishsoup,stew orbroth. In German, it is known asEierstich and is used as a garnish in German Wedding Soup (Hochzeitssuppe).[3]Chawanmushi is aJapanese savoury custard, steamed and served in a small bowl or on a saucer.Chinese steamed egg is a similar but larger savoury egg dish.Bougatsa is a Greek breakfastpastry whose sweet version consists ofsemolina custard filling between layers ofphyllo.
In Peru,leche asada ("baked milk") is custard baked in individual molds.[4] It is considered a restaurant dish.[5]
In French cuisine
French cuisine has several named variations on custard:[6][7]
Crème anglaise is a light custard made with eggs, sugar, milk, and vanilla (with the possible addition of starch), with other flavoring agents as desired
With cream instead of milk, and more sugar, it is the basis ofcrème brûlée
Custards baked in pastry (custard tarts) were very popular in theMiddle Ages, and are the origin of the English word 'custard': the French termcroustade originally referred to the crust of a tart,[8] and is derived from the Italian wordcrostata, and ultimately the Latincrustāre.[9]
Examples includeCrustardes of flessh andCrustade, in the 14th century English collectionThe Forme of Cury. These recipes include solid ingredients such as meat, fish, and fruit bound by the custard.[10][11] Stirred custards cooked in pots are also found under the namesCreme Boylede andCreme boiled.[11] Some custards especially in theElizabethan era usedmarigold (calendula) to give the custard color.[12][13]
In modern times, the name 'custard' is sometimes applied to starch-thickened preparations likeblancmange andBird's Custard powder.
Chemistry
Stirred custard is thickened bycoagulation 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 andsyneresis that will result in acurdled custard.[14]
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.[15] 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 60–80 °C (140–176 °F).[16]
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.[15]
If the mixture pH is 9 or higher, the gel is too hard; if it is below 5, the gel structure has difficulty forming becauseprotonation prevents the formation ofcovalent bonds.[17]
Physical-chemical properties
Cooked (set) custard is a weakgel, viscous, andthixotropic; while it does become easier to stir the more it is manipulated, it does not, unlike many other thixotropic liquids, recover its lost viscosity over time.[18] On the other hand, asuspension of uncooked imitation custard powder (starch) in water, with the proper proportions, has the oppositerheological property: it is negative thixotropic, ordilatant, allowing the demonstration of "walking on custard".[19]
^Beck, Simone; Bertholle, Louisette; Child, Julia (1964) [1961]. "Desserts and Cakes".Mastering the art of French cooking. New York: Alfred A. Knopf, Inc.
^Gisslen, Wayne (2013). "Basic Syrups, Creams, and Sauces".Professional baking (6th ed.). Hoboken, NJ: John Wiley & Sons.ISBN978-1-118-08374-1.OCLC753351232.
^Kovacs-Nolan, Jennifer; Phillips, Marshall; Mine, Yoshinori (2005-11-01). "Advances in the Value of Eggs and Egg Components for Human Health".Journal of Agricultural and Food Chemistry.53 (22):8421–8431.doi:10.1021/jf050964f.ISSN0021-8561.PMID16248532.
^Longrée, Karla; Beaver, Sharie; Buck, Paul; Nowrey, Joseph E. (1966). "Viscous Behavior of Custard Systems".Journal of Agricultural and Food Chemistry.14 (6):653–659.doi:10.1021/jf60148a033.