19Fats and oils

Almost every station in a kitchen reaches for fat. It carries heat in the fryer and the sauté pan, it makes pastry tender and cakes light, and it carries flavor in a dressing. A fat that stays liquid at room temperature is called an oil.

19.1 What fats and oils are

Built from three elements

Like sugars and starches, fats and oils are made of carbon, hydrogen and oxygen. In baking books the word lipid usually just means fat, so "the lipid content of eggs" is the fat in eggs.

Fatty acids decide how a fat behaves

Every fat and oil has its own mix of fatty acids, and that mix sets how firm or runny it is. Beef fat is mostly stearic acid. Seed oils are mostly linoleic acid. Fatty acids are also sorted by length into short, medium and long chains.

Each fatty acid has its own melting point. In a fat made of many kinds, they soften one after another as it warms, so the fat melts slowly. In a fat made of one kind, or several very alike, everything melts at nearly the same moment. Coconut fat is the example: solid one second, liquid the next.

Melting points of three common fatty acids.

Saturated and unsaturated

These words describe how fully the carbon atoms in a fatty acid are bonded to hydrogen. One way to sort fatty acids is to count the double bonds between carbons:

• Saturated: no double bonds. Stearic acid is the usual example.
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• Monounsaturated: one double bond. Oleic acid is the usual example.
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• Polyunsaturated: two or more. Linoleic acid is the usual example.

Saturated fat is found in:

• meat: beef, chicken, lamb, pork and veal;
• dairy foods such as butter, cheese and whole milk;
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• lard and shortening;
• coconut, palm and palm kernel oils.

Monounsaturated fat is found in:

• avocados;
• nuts and seeds such as almonds, cashews, pecans and peanuts;
• oils such as olive, canola, sesame, peanut, sunflower and safflower.

Polyunsaturated fat is found in:

• fatty fish such as herring, mackerel, salmon, trout and smelt;
• fish oils;
• the same nuts and seeds;
• canola, corn, flaxseed, soybean and sunflower oils.

On health, the case against saturated fat is not settled, though the usual view is that less is better. Swapping saturated and trans fats for unsaturated ones has been shown to help lower cholesterol, and the dietary guidelines of the United States government give advice on choosing fats. Unsaturated fats also supply omega-3 and omega-6 fatty acids. Even so, too much of any fat means too many calories.

There is a kitchen problem hidden in this. Oils low in saturated fat do not stand up well to the long, high heat of a deep fryer.

Hydrogenation and trans fat

Manufacturers solve that problem with hydrogenation: hydrogen gas is forced into an oil, it bonds to the carbon, and the liquid oil becomes a solid fat. Adding hydrogen changes the melting point. That lets one fat stay workable in a cool bakery and a hot one, or in a cold climate and a warm one.

Partial hydrogenation, which also turns liquid oil into solid fat, creates trans fat. Trans fat raises LDL, the "bad" cholesterol, as saturated fat does. It also lowers HDL, the "good" cholesterol, and low HDL is itself a risk for heart disease. In the American diet, trans fat came mostly from fried foods such as doughnuts, from baked goods and from stick margarine. In the United States, the Food and Drug Administration requires the trans fat content to be shown in the nutrition facts table on a label.

Where fats come from and how they are refined

Edible fat comes from animals and from plants. On the animal side there are fish, sheep, pork and beef, with pork and beef the chief sources across North America. From plants come sunflower, soya bean, safflower, peanut, palm fruit, palm kernel, olive, corn, cotton, coconut and canola.

Refining takes a raw fat through these steps:

• An alkali neutralizes the free fatty acids.
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• The color is taken out.
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• The fat is hydrogenated.
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• Odors are removed (deodorizing).
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• Chilling and beating whitens and softens the fat. This is done in a machine called a votator, which cools and kneads liquid margarine.
• The fat is held in storage so its crystals form correctly. This rest is called tempering.

Emulsifiers

Oil and water do not normally mix. An emulsifier helps them combine into one stable mixture. Egg yolk holds a natural one, lecithin. Makers add mono- and diglycerides to many hydrogenated fats. The fat then forms a finer, more even structure, takes up more sugar and holds more liquid. Such emulsified shortenings suit cakes and icings, but not the deep fryer.

How fat goes bad

Rancid means a fat has spoiled and tastes unpleasant. Air and heat cause it. Unsalted butter left out of the refrigerator goes rancid fast, above all in a hot climate.

The air does its damage through oxidation, and some metals speed it up. Copper is one, which is why doughnuts are never fried in a copper pan. Some oils carry natural antioxidants, for example tocopherols, one of which is vitamin E, but processing often destroys them. Makers then add synthetic ones, commonly BHA and BHT, to slow rancidity.

Frying fat also breaks down by hydrolysis, a reaction with water. The water comes out of the food being fried. It splits fatty acids away from their glycerol, and as these free fatty acids build up in the fryer, the fat starts to taste bad and gives the same taste to everything cooked in it. So between batches of doughnuts, switch the fryer off or set it to standby. Heavy flour on the food, and crumbs that break off it, also wear the fat out.

Smoke point and stability

The smoke point is the temperature at which a fat first gives off smoke. It is not fixed for life: as a fat breaks down, its smoke point falls. A fat's stability is how long it lasts in use, which matters most for frying fats. A smoke point of 220 to 230°C (428 to 446°F) marks a fat as highly stable.

19.2 The fats a kitchen uses: butter, lard, shortening, oils

Butter

Butter starts as cream, which may be sweet, neutralized or ripened, pasteurized and brought to 30 to 40% fat. Churning, or whipping too far, makes the fat clump away from the watery part, which is buttermilk. The fat is washed and kneaded until it is smooth and plastic. Color is often added to make it look richer, and salt helps it keep.

Butter must be at least 80% milk fat by weight. The only other ingredients allowed are milk solids, salt, air or an inert gas, permitted color and permitted bacterial culture. Its grade name is Grade 1. The rules also name two kinds: whipped butter, with air or inert gas beaten evenly through it and up to 1% added edible casein or caseinates, and cultured butter, made from cream with a permitted bacterial culture added.

Sweet butter, also called unsalted, is made from cream with very little acid, and has no salt. It is used where butter must be the only fat, as in French buttercream. Keep it in the refrigerator.

For flavor, butter is the best baking fat. Its drawbacks are cost and its handling. It creams moderately well, so allow up to five extra minutes of creaming in a cake for full volume. Its plastic range is narrow, only 18 to 20°C (64 to 68°F): at 10°C (50°F) it is nearly too hard to work, and by 27°C (80°F) it is too soft, and it is hard to work in hot weather. Adding an emulsifier, about 2% of the flour weight, helps a butter cake.

Butter is a dairy product. Dairy products are kept refrigerated, between 2 and 4°C (36 and 39°F), covered and in their own area, because the fat in them picks up strong smells nearby. The signs of spoiling are plain: butter turns darker and smells sour.

For why whole butter is a poor fat at high heat, and for clarified butter and its smoke point, see chapter 7: Dry heat with fat

Lard

Lard comes from the fatty tissue of pigs and holds 12 to 18% water. Worry about diet has made it less popular than it was, but bakers still use it in yeast doughs, in pie pastry and for greasing pans.

Its wide plastic range is its strength: you can work lard into a pie dough at fairly low temperatures, which butter will not allow. Its weaknesses keep it out of cakes. It is fibrous and does not cream well, and some grades have a strong flavor of their own.

Margarine

Margarine is made mostly from vegetable oils, partly hydrogenated, with a little milk powder and bacterial culture for a buttery taste. It holds 80 to 85% fat, and the rest is much like butter. It can be bought white but is usually colored. Bakers use several kinds:

• General purpose margarine melts at a low temperature and blends into dough for everyday baking.
• Cake margarine creams very well.
• Roll-in margarine is plastic enough to be rolled into Danish pastry.
• Puff pastry roll-in is the waxiest kind, with the highest melting point.

Margarine once came only in solid blocks heavy in saturated and trans fat. Most margarine now comes in tubs: soft, spreadable and not hydrogenated, so low in both. Take great care before swapping a soft tub margarine for a solid one in a recipe.

Shortening

Since hydrogenated vegetable oil was invented early in the 20th century, shortening has come to mean almost only that. Shortening and lard have much in common:

• Both are semi-solid fats.
• Both are close to 100% fat, where butter and margarine are about 80%.
• Both have a higher smoke point than butter or margarine.
• Because they hold less water, both spatter less, which makes them safer for frying.

Shortening was long made from partially hydrogenated oils, so it carried trans fat. One leading brand brought out a low-trans version in 2004, and in January 2007 reformulated all its products to under one gram of trans fat a serving. Many other brands have changed since 2006. Shortening without hydrogenation can be made from palm oil.

Hydrogenated shortenings are the main fat of commercial baking. What they share:

• Their oils are largely those used for margarine.
• They cream well.
• They contain no water.
• They keep for six to nine months.
• Each is hydrogenated to suit its job.

There are three main kinds:

• Emulsified shortening, also called high-ratio fat. Its added mono- and diglycerides spread the fat finely, so a cake can carry a lot of sugar and liquid. The cake comes out fine-textured, light, high, moist for longer and tender. It is also the usual fat in many white icings. High-ratio fats blend well with ingredients that attract water, such as sugar and starch.
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• Roll-in pastry shortening, or special pastry shortening (SPS). It is semi-waxy, with a large plastic range, and it stretches and lifts well, so it is used in puff and Danish pastry, where layers of fat and dough are rolled together. The choice is always a trade between cost, taste and lift. A roll-in that does not cling to the palate may melt too low to give a puff pastry its full rise.
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• Deep-frying fat. Its smoke point reaches as high as 250°C (480°F). It resists heat and breakdown, leaves no off taste, is not greasy once the food is cold, and contains an agent to stop foaming.
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Oils and coconut fat

Oil labels follow set rules:

• "Vegetable oil" may name a blend of more than one plant oil used in another food.
• In a cooking, salad or table oil, each oil must be named, such as canola or corn.
• Coconut, palm, palm kernel and peanut oil, and cocoa butter, must always be named.
• If any oil in a blend has been hydrogenated or modified, the label must say so, as in "hydrogenated vegetable oil".

In baking, oil goes into:

• chemically leavened batters such as muffins;
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• doughs, in place of solid fat;
• short sponges, in place of butter.

Coconut fat has a very small plastic range and a fairly low melting point, yet it is hard. Bakers use it to firm up buttercream. It can be made to melt at different points, usually 32 to 36°C (90 to 96°F).

Melting point and blends

A fat that melts low, like butter, is hard to handle in the heat. A fat that melts very high is unpleasant to eat because it clings to the roof of the mouth. A melting range of 40 to 44°C (104 to 112°F) is a fair middle way, though newer fats can melt higher without clinging.

Most fats you buy are blends. Some are all plant oils; others mix plant and animal fat, often about nine parts plant to one part animal, though that is not a rule. Such mixtures used to be called compound fats.

What fat does in baking

• Tenderizes. Enough fat "shortens" the strands of gluten in flour, which is where shortening gets its name. Lard was the classic example.
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• Holds air. Beaten with a paddle, a fat that creams well traps many tiny air pockets, and the better it creams, the lighter the cake.
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• Lubricates. Fat lets the gluten network stretch, and makes dough easier to mix and handle.
• Keeps it moist. Fat slows drying in both dough and batter. A shortening that is all fat does this better than butter or margarine.
• Feeds. Fat is a dense source of energy and carries fatty acids the body needs.
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19.3 Cooking oils and smoke points

Cooking oils are refined from seeds, plants and vegetables. When you buy one, weigh four things:

• what it is for;
• its smoke point;
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• its flavor;
• its price.

Smoke point and flash point

Heat breaks a fat down, and each fat has its own limit. As it breaks down, its triglycerides come apart into separate fatty acids. These give the fat an off taste, and that taste passes into the food. The smoke point is the temperature where this breakdown begins and the fat starts to smoke. Higher still is the flash point, where the fat catches and small flames show on its surface. For hot work such as deep-frying and sautéing, choose a fat with a high smoke point.

For frying temperatures, the fire point and safe handling of a fryer, see chapter 8: Deep-fryer safety

Flavor against price

Cost and taste pull against each other. A salad dressing could be made with corn oil or with walnut oil. Corn oil is cheaper; walnut oil tastes stronger and more of itself. The choice weighs one against the other.

The kinds of oil

Vegetable oils are drawn from plants such as soybeans, corn, peanuts, sesame seeds, cottonseed and grape seeds, either by pressing or with chemical solvents. They are then refined to take out unwanted color, smell and taste. The result has almost no smell and a neutral flavor, and since no animal product is involved, no cholesterol. Labels tell you what is in the bottle:

• Pure, as in "pure corn oil": one oil only.
• Vegetable oil: a blend of oils from several plants.
• Salad oil: a highly refined blend of vegetable oils.

Canola oil is made from rapeseed. It has no flavor, no cholesterol, a high share of monounsaturated fat and a high smoke point, so it is a good oil for frying and for cooking in general.

Nut oils, such as walnut and hazelnut, are almost always sold pure rather than blended, and a good one smells and tastes strongly of its nut. Use them to flavor dressings, marinades and finished dishes. Heat dulls their flavor, so they are not for frying or baking. They turn rancid quickly, which is why they come in small bottles.

Olive oil

Olive oil is pressed from a fruit, the olive, rather than from a seed, nut or grain. Most comes from Spain, Italy, France, Greece and North Africa, with a little from California. As with wine, its color and taste change with the kind of tree, how ripe the olives are, the soil, the climate and the maker. Color runs from deep green to nearly clear, set by ripeness at pressing and by how far the oil is refined, but color tells you nothing about taste. Choose by the dish: some foods want a strong oil, others a mild one. A good olive oil is thicker than a refined vegetable oil without feeling greasy.

The label grades show how acidic the oil is (less is better) and how it was made:

Olive oil grades.

Flavored oils

Flavored oils, also called infused oils, carry basil or other herbs, garlic, citrus or spice. Serve them as a dip for bread, cook with them, or use them to accent a marinade, dressing or sauce. They are usually based on olive oil, for its taste, or on canola. The best commercial ones are made by drawing the aromatic oils out of the flavoring, blending them into a good oil, and spinning out any bits in a centrifuge. That gives a stronger taste than steeping the flavoring in the oil. Store a flavored oil as you would any good oil.

For potentially hazardous foods and the danger zone, see chapter 2: Potentially hazardous foods

Storing oils and fats

Fat that spoils goes rancid: air, light or heat change it, and it smells and tastes bad. Some fats turn faster than others, but every fat keeps better refrigerated and shielded from moisture, light and air. That is why some oil comes in green or yellow glass, which blocks the light that harms it.

• An oil that turns thick and cloudy in the refrigerator has come to no harm. It clears again at room temperature.
• Keep stored fats covered, or they take on the smells around them.
• Store a flavored oil the same way as any good oil.

For straining used frying oil and the off taste it develops, see chapter 8: Deep-fryer safety