Water sets a ceiling
Moist-heat methods cook food in liquid or in steam. They share one defining feature, which the USDA Food Safety and Inspection Service (FSIS) states plainly in its guidance on cooking at altitude: water cannot get hotter than its own boiling point, which is 212°F (100°C) at sea level, unless it is under pressure in a pressure cooker. Turning the burner up under a boiling pot does not make the food cook faster; the water just boils away sooner.
That ceiling is both the strength and the limit of moist heat. It is gentle and even: food in simmering liquid cannot scorch, and it can sit for hours without drying out. But it cannot brown. The FDA notes that boiling and steaming do not typically form acrylamide, a compound that forms from sugars and an amino acid in high-temperature frying, roasting and baking. The browning reactions that give a roast its crust simply do not happen at the temperature of simmering water. That is why many moist-heat recipes start with a dry-heat step.
Boiling and simmering
The Iowa State University food preparation lab manual's glossary gives clear working definitions. To boil is to heat a liquid to its boiling point, until bubbles break the surface, and also to cook food in that boiling liquid. To simmer is to cook food in liquid over gentle heat just below the boiling point, low enough that tiny bubbles are just beginning to break the surface.
Those descriptions are what to watch for, and they are more useful at the stove than a number. A full, rolling boil is fast and turbulent, with large bubbles breaking all over the surface, and it tumbles the food about. A simmer is calmer: small bubbles rising and just breaking at the surface. Long-cooked dishes, such as the stews and braised meats in the Iowa State manual, are cooked at a simmer, where the food is heated steadily without being knocked about and the liquid does not boil away as fast.
The usual way to get a simmer is to bring the liquid to a boil, then turn the heat down until the bubbles slow to that gentle state. The recipes in the Iowa State manual follow that pattern again and again: bring to boiling, reduce the heat, cover and simmer.
Poaching
Poaching, in the Iowa State definition, means cooking food by gently simmering it in liquid at or just below the boiling point, with the amount of liquid and the exact temperature depending on what is being poached. It suits food that needs to keep its shape: the liquid moves only gently, so the food is not broken up the way it might be in a rolling boil.
Blanching and parboiling
Two short moist-heat steps are often used before another method. To blanch, in the Iowa State glossary, is to cook raw ingredients in boiling water very briefly. Blanched vegetables are usually plunged straight into ice water to stop the cooking, which keeps their colour and crunch. To parboil is to boil food briefly so that it cooks only partly. The glossary gives dense foods such as carrots and potatoes as examples: parboiled first, they can then be added at the last minute to a quicker-cooking dish, so that everything finishes at the same time.
Steaming
Steaming cooks food in the vapour above boiling or gently bubbling water, rather than in the water itself. The Iowa State glossary says steaming retains flavour, shape, texture and nutrients better than boiling or poaching, and Mississippi State University Extension notes that steaming in just a little water keeps vitamins inside vegetables.
Mississippi State's method for vegetables is simple: put them in a shallow pan with a small amount of water in the bottom, cover with a lid or foil, keep the water bubbling gently over medium-low heat, and cook just until tender. Green beans, spinach and corn on the cob are among its suggestions. A steamer basket that holds the food above the water works on the same principle.
Steam burns
Steam can burn you. Mississippi State Extension gives this warning about lifting the lid from a dish of steamed or microwaved vegetables. Tilt a lid away from your face and hands so that the steam escapes on the far side.
Braising and stewing
Braising and stewing combine the two families of methods. The Iowa State glossary defines braising as cooking food tightly covered, in a small amount of liquid, at low heat for a long time, and notes that the food is sometimes browned in fat first. The long, slow cooking tenderizes meat by gently breaking it down, the liquid keeps it moist, and the liquid can then be turned into a sauce. Stewing is similar but uses more liquid, usually in a covered pot, until the food is tender.
The browning step matters because the simmering liquid cannot provide colour. The Iowa State lab recipes for a beef stew and for braised round steak both start the same way: brown the meat thoroughly in a little hot oil, then add liquid, cover and simmer on low heat for an hour or more, adding water if the level drops.
Why tough cuts need slow, wet heat
The Iowa State manual explains why some cuts of meat are cooked by moist heat. Less tender cuts come from more heavily used muscles. They have larger muscle fibres, less marbling and more connective tissue. Two kinds of connective tissue behave very differently:
- Collagen softens with heat and moisture and breaks down into gelatin. Given enough time in a moist, gentle heat, it turns a tough cut tender and gives the cooking liquid body.
- Elastin, the gristle, does not break down with heat or moisture. It is usually trimmed off before cooking.
That is why a cut such as beef chuck or pork shoulder, which would be chewy if cooked quickly in a pan, becomes tender after a long braise. It is also why braising takes time: the collagen needs hours, not minutes, to break down.
Cooking in water at altitude
FSIS explains that as altitude rises, air pressure falls and water boils at a lower temperature. Food cooked by boiling or simmering is therefore cooking at a lower temperature and takes longer. FSIS says that at altitudes above 3,000 feet, recipes may need changes in time, temperature or ingredients, and that liquids also evaporate faster, so covering food during cooking helps keep moisture in. Turning up the heat will not compensate, for the reason given at the start of this guide.
Safety in the pot
Cooking in liquid does not change the safe minimum internal temperatures in the FSIS chart. Meat and poultry in a stew still need to reach the figures on the safe temperatures page, such as 165°F (73.9°C) for poultry, and a thermometer is still the way to check, especially for large pieces. Because long-cooked braises and stews are often made in large batches, the leftover rules in the kitchen food safety guide apply: divide them into shallow containers and refrigerate them within 2 hours.
Example: a simple braise
Worked example
An illustration of the method, not a tested recipe, and it describes no real kitchen. A cook has a piece of beef chuck, a cut with plenty of connective tissue.
- They trim off any thick gristle, which will not soften however long it cooks.
- They pat the meat dry and brown it on all sides in a little hot oil in a heavy pot, for colour and flavour.
- They add liquid to come part of the way up the meat, bring it to a boil, then turn the heat down to a gentle simmer with tiny bubbles.
- They cover the pot tightly and let it cook slowly, checking now and then that the liquid has not boiled away.
- When a fork slides in easily, the collagen has broken down. They lift out the meat and reduce the liquid at a stronger boil to make a sauce.
Brown first with dry heat, then cook long and slow with moist heat: that one pattern covers pot roasts, stews and most braised dishes. The next guide moves from the stove to the cutting board.
Up next on the range: Knife skills and kitchen safety