Cream is one of the cook's or baker's best friends. It adds richness and body to almost any food or sauce, and makes baked goods soft and tender when added to a recipe. Enriched creams, including clotted cream, creme fraiche and mascarpone, occupy a cherished place in the kitchen. Each has its own distinct character.
Cream Rises to the Top
Milk is mostly water, with whey proteins, casein proteins and globules of fat suspended in it. That fat is the lightest portion of the milk, and unless the milk is homogenized, it always rises to the top and forms a distinctly richer layer. That's the cream, and the longer your milk sits -- especially at warm temperatures, which speed separation -- the richer and thicker it becomes. Historically, dairy farmers skimmed the cream from shallow pans of milk and let it sit again, skimming it repeatedly to separate the richest portion. Modern dairies use massive centrifuges to perform the same task in seconds, and produce creams with a consistent percentage of milk fat. Then the cream can be processed into differing products.
Heating and Cooling
When heavy whipping cream is warmed gently, its fat globules float to the top and cluster together, gradually forming a firm layer at the top. This process has been harnessed to produce the famous clotted cream of Devon and Somerset. The cream must be brought to a near boil, then left to cool for a day. The end result is very rich, at about 60 percent fat, and contains both softly creamy and firmer butter-like areas. It's usually spread on scones or other baked goods, or spooned onto fruit or fruit preserves. This is the simplest and most natural way to create a thickened cream, but creme fraiche and mascarpone employ different techniques.
The Good Bugs
Instead of manipulating cream's own tendency to thicken, creme fraiche is produced by the activity of beneficial bacteria. The cream is gently heated and then inoculated with bacterial cultures, mostly of the Lactococcus family. They consume the cream's natural sugars and produce lactic acid in exchange. This gentle acidity makes the cream thicken and develop a mild but refreshing tang. Since it relies on bacteria rather than concentration for its thickening, creme fraiche averages only about 40 percent milk fat. It's much lighter than clotted cream or mascarpone, but still rich enough to be heated and used in sauces without curdling.
Heat and Stir
Mascarpone takes a third approach to thickening cream and making it rich and luscious. The cream is brought to a simmer until approximately a third of its original volume has evaporated. Then, instead of relying on bacteria or resting time to make it thick, an acid ingredient such as vinegar or cream of tartar is mixed into the warm, extra-rich cream. The acidity causes the cream to congeal to a thick, almost stiff texture, while retaining its mild and creamy flavor. Concentrating the cream makes mascarpone the richest of the three, at 75 percent milk fat. It's most familiar as a sweetened filling for desserts such as cannoli, but like butter it also works well with savory flavors.