Cheese and Cream in Cooking.
A grated aged cheese stirred into a boiling sauce turns to rubbery strings in a pool of oil. Off the heat, with a spoon of starch, it melts silky.
Cheese is casein holding fat and water (XIV.6). Warmed, its fat softens first (around 30 °C, IX.2), then the casein network loosens and the cheese flows. Heated further, the casein contracts, squeezes out fat and water, and clumps into strings: the cheese "breaks". Young, moist cheeses (mozzarella, young cheddar, gruyère) melt well and break late; aged, dry ones (parmesan) hardly flow and break readily, so they are grated finely and added off the heat. Three helpers keep melted cheese smooth: starch, which coats the protein (mac and cheese thickened with a roux); acid and wine, which loosen casein (fondue); and emulsifying salts such as sodium citrate, which bind calcium so the casein disperses — the secret of processed cheese and of glossy cheese sauces.
Cream and milk differ in heat for the same reason. Cream with 30–40 % fat has little protein for its fat and its globules shield the casein: it can be boiled, reduced and even acidified without splitting, which is why cream sauces are so forgiving (XXII.7). Milk, with as much protein as fat, curdles when boiled with acid or salt — milk sauces split with wine or tomato unless thickened with starch first. The workshop melts cheese.
Below: the state of melted cheese against its temperature for a young and an aged cheese, with and without sodium citrate (a teaching model: flow begins above the softening point, breaking above a point set by age and helped by citrate), and the state at your settings.
- Explain how cheese melts and breaks.
- Choose cheeses for melting.
- Use starch, acid or emulsifying salts.
- Explain why cream sauces survive boiling and milk sauces split.
Off the boil, finely grated, helped
In this teaching model, at 75 °C a young cheese is smooth (0.96) while an aged one has begun to break (0.16); with 2 % sodium citrate the aged cheese stays smooth even at 90 °C (0.84). The practical rules follow: grate finely; take the sauce off the boil before adding cheese; add it in handfuls, stirring; blend aged cheeses with a younger, moister one; and use a starch-thickened base (a béchamel, XXII.6) or a little acid, or a pinch of sodium citrate, to keep it silky.
For cream and milk: reduce cream freely for pan sauces and add acid at the end; thicken milk-based sauces with flour or starch before adding wine, tomato or lemon; never boil a milk sauce hard after acid goes in. Yoghurt in curries splits when boiled for the same reason — stir in a spoon of the hot sauce first to temper it, add it off the heat, or stabilise it with a little flour (XVI.6).
Melt grated parmesan into two small pans of hot milk: one at a simmer, one off the heat with a pinch of cornflour stirred in first. Compare: strings and oil against a smooth sauce.
Terms
- Breaking (cheese)
- Melted cheese turning stringy and greasy as casein contracts.
- Sodium citrate
- An emulsifying salt that keeps melted cheese smooth.
- Splitting (sauce)
- A sauce separating into curds and liquid or fat.
- Tempering
- Warming a sensitive ingredient gradually before adding it to heat.
Sources
- A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.
- H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.