14.1 Milk and what is made from it

Milk recipes → Condensed and evaporated milk recipes →

Why kitchens buy milk in different forms

Fresh milk is heavy and bulky. It goes off quickly and must be kept in a fridge, which costs money. For these reasons it is a fairly expensive ingredient, and most bakeries today use dried skim milk or buttermilk powder instead.

Milk is named by how much fat it holds. Each of these grades has more than 8.25% milk solids:

Fat grades of milk.

Homogenized and pasteurized

Pasteurization heats milk to kill harmful bacteria, including those that can carry tuberculosis and fever from cows to people. The French chemist Louis Pasteur developed it in 1859. In one method, milk is heated above 71°C (160°F), held there for a set time, and then cooled straight away to 10°C (50°F) or colder.

Three heat treatments are in use today:

• HTST (high temperature, short time, also called "flash"): 72°C (161°F), held for 15 seconds. When a carton just says "pasteurized", this is usually the method used.
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• HHST (higher heat, shorter time): continuous heat, usually above 100°C (212°F). It gives products a longer life in the fridge, sold as ESL, which stands for extended shelf life.
• UHT (ultra-high temperature): 140°C (284°F) for four seconds. The milk is sprayed into a chamber of hot steam under pressure, cooled at once in a vacuum, and sealed in a sterile, airtight pack. UHT milk is sterilized, not just pasteurized, and can sit for several months with no fridge.
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Cream

Cream is sold by how much milk fat it holds. The names below are the ones used in Canada.

Cream types in Canada.

Names change from place to place, so read a recipe's origin. What the United States calls light cream, Canada mostly calls half-and-half; in Canada, "light cream" means a low-fat cream. You can make it by mixing milk with half-and-half. Quebec sells a country cream with 15% fat, and 18% cream can stand in for it. British recipes may ask for double cream, at about 48% fat, which is hard to find in Canada; use whipping or heavy cream.

Other figures for whipping cream are slightly different: 30–36% fat for light whipping cream and 36–40% for heavy.

Whipping cream whips well and can be piped. Cooks use it for custards, cream fillings and sweets. The fat level matters: with much less fat than about 32%, cream will not whip at all. It whips best when cold and when it is 48 to 60 hours old. You can add sugar, a flavor and a stabilizer as you whip. Check the carton first. Some creams already contain an agent such as carrageenan, and then no more stabilizer may be needed.

Cultured milk and cream

Buttermilk can be made in two ways. One way is to churn cream into butter and keep the liquid that is left over; this is where the name comes from. Today most buttermilk is made the other way, by adding a culture to milk to sour it. Cultured buttermilk has 0–1% fat. Buttermilk is more acidic than milk: its pH is 4.6, where milk's is 6.6. In baking, that acid reacts with baking soda to make carbon dioxide gas, which makes the batter rise.

Sour cream is cream soured with lactic acid. The acid sets the cream's proteins into a soft gel. Makers may add gums and starches to make it thicker and to stop the watery whey from separating out. Bakers put it in pastry doughs, coffee cakes and cheesecakes. Low-fat sour cream, at about 7–10% fat, usually works in baking too, though it is wetter and tastes less rich.

Figures for the fat in regular sour cream differ. One puts it at 5.5% to 14%. Another puts it at 18–20%.

Crème fraîche (French for "fresh cream") is a soured cream with 30–45% fat and a pH near 4.5. The traditional way is to leave unpasteurized milk in a pan at room temperature so the cream rises. About 12 hours later the cream is skimmed off, already thick and mildly sour from the milk's own bacteria. To make a substitute, stir a little cultured buttermilk or sour cream into whipping cream, leave it somewhere warm for at least 10 hours, then refrigerate it.

Dried and canned milk

Milk powder is made from whole milk, skim milk, buttermilk or whey. Each is pasteurized, concentrated in an evaporator, and then dried by spraying or on rollers. Each powder has limits it must meet:

• Whole milk powder: at least 95% milk solids, no more than 5% moisture, and at least 2.6% milk fat. It may also contain added vitamins A and D, and up to 0.5% lecithin, an emulsifier.
• Skim milk powder, also called non-fat dry milk: at least 95% milk solids, no more than 4% moisture and 1.5% fat.
• Buttermilk powder: at least 95% milk solids, no more than 3% moisture and 6% fat.
• Whey powder: mostly milk sugar, whey proteins, minerals and vitamins. It keeps about half the nutrients of the milk it came from.

To turn powder back into liquid milk, put the water in first and whisk the powder in straight away. If you wait, or pour water onto the powder, it tends to clump. Use water at about 21°C (70°F).

Reconstituting milk powder.

Evaporated milk, sometimes called concentrated milk, can be made from whole, partly skimmed or skim milk. About 60% of the water is taken out by evaporation. The milk is then homogenized, cooled, adjusted, canned, and sterilized in the can for 10 to 15 minutes at 99–120°C (210–248°F). It is darker than fresh milk, because at high heat the milk's protein and its sugar brown together. Small amounts of disodium phosphate or sodium citrate keep the milk from curdling during heating and storage. In Canada it must hold 7.5% milk fat and 25% milk solids.

Sweetened condensed milk is milk condensed to a third of its volume, with sugar added. It is thick and sweet. It holds about 40% sugar, at least 8.5% milk fat and at least 28% milk solids. Other figures give it 44% added sugar and more than 28.5% milk solids.

Lactose, the sugar in milk

Lactose is the natural sugar of milk. It tastes much less sweet than ordinary sugar (sucrose), and yeast cannot ferment it. So bread dough made with skim milk powder needs some added sugar, or it will ferment very slowly. Lactose does brown easily in the oven, which gives bread made with milk a darker crust. Bakers use 2–8% skim milk powder by flour weight in yeast doughs and up to 15% in cakes.

Lactose is also sold on its own, dried or as crystals. It is useful in baking in several ways:

• It brings color and texture without making food too sweet.
• It can take the place of up to half the sucrose in a recipe, or all of it in pie pastry.
• In pie crusts it gives good color, a more tender crust and less sogginess.
• In cakes and muffins it adds body and volume.
• It holds on to flavors that would otherwise escape, so food tastes stronger.

Milk, heat and acid

Milk holds two kinds of protein, casein and whey protein. Acid or the enzyme rennin makes milk curdle: it separates into solid curd and liquid whey. That is how cheese begins. How rennin and acid set milk proteins is explained with the other proteins. see chapter 7: Milk and soy

The isoelectric point of casein is pH 4.6. Milk itself sits at pH 6.6. Tomato juice is an acid food. Combine it with milk three ways: both cold, hot juice into hot milk, and hot milk into hot juice. Look at each mix at once and again after 15 minutes.

For cream of tomato soup, heat the tomato juice and the white sauce separately. Then stir the hot juice slowly into the hot sauce, and serve the soup at once. A good result is smooth, with no curdling, lumps or skin.

Storing milk and cream

Dairy is kept in the fridge at 2–4°C (36–39°F). A few rules keep it in good condition:

• Its fat soaks up strong smells, so keep it covered and in its own area.
• A fridge just for dairy is better than sharing the vegetable cooler.
• Rotate stock when new dairy arrives.
• Order it close to when you will use it, ideally every day.

Dairy that is going off turns darker and smells sour. The danger zone and the general rules for the fridge are set out with the rest of food safety. see chapter 2: The danger zone