Sous-vide at home: the time and temperature behind a safe low-heat cook

Sous-vide means “under vacuum.” Food is sealed in a plastic bag and cooked in water held at a fixed temperature, usually by a circulator clipped to the side of a pot. Because the water never runs hotter than the setting, a steak cannot overshoot. The same property makes the method a food-safety question, since a water bath can hold meat for hours at temperatures bacteria are perfectly comfortable in.

The numbers on the consumer chart

The USDA’s Food Safety and Inspection Service (FSIS) publishes the minimum internal temperatures most American cooks know: 165°F for all poultry, 160°F for ground meat, 145°F for fish and shellfish, and 145°F for whole cuts of beef, pork, veal and lamb followed by a rest of at least three minutes. At 165°F, Salmonella in chicken dies off in under ten seconds, which is why the chart can be simple. But the chart describes one point on a curve. Heat kills bacteria as a function of temperature and time together, and at lower temperatures the same kill takes longer. Sous-vide cooking lives at the long, low end of that curve.

Time at temperature

For processors, FSIS publishes time and temperature tables for cooked ready-to-eat poultry, built to reduce Salmonella by a factor of ten million (a “7-log” reduction). For chicken with about 2 percent fat, the required holding times run as follows:

Fat protects bacteria from heat, so fattier meat needs longer. At 140°F, chicken with 10 percent fat needs 32 minutes instead of 25.7. Turkey has its own column in the tables, and above about 141°F it needs longer than chicken.

The FDA Food Code, which state health departments adopt for restaurants, has a comparable table for whole roasts of beef, pork and lamb: 112 minutes at 130°F, 36 minutes at 135°F, 12 minutes at 140°F, and 4 minutes at 145°F.

When the clock starts

Every holding time in those tables counts from the moment the center of the food reaches the temperature. Heat moves into meat by conduction, and the time it takes rises roughly with the square of the thickness, so a piece twice as thick needs about four times as long just to come up to temperature. A recipe that gives one time for chicken breast is assuming a particular thickness.

The Food Safety Authority of Ireland, in its sous-vide factsheet for caterers, recommends working out cooking times with the bath fully loaded and the food at its coldest, a good habit at home too, since a crowded pot of cold bags drags the water temperature down. The same factsheet advises against using the method for whole birds, because the cavity prevents even heating, and for minced meat.

Whole cuts, ground meat and the surface

On an intact steak or chop, bacteria sit mostly on the outside. A steak cooked sous-vide at 130°F and then seared hard in a pan has had its surface heated well past any kill point, which is the reasoning behind the lower risk usually attached to rare whole-muscle beef, although FSIS still advises 145°F for everyone. Grinding, needle tenderizing and marinade injection all push surface bacteria into the middle. Beef treated that way must be labeled “mechanically tenderized” in American stores, and it needs the same care as ground meat.

The danger zone and the low floor

FSIS defines the “danger zone” as 40°F to 140°F, the range in which bacteria grow fastest, doubling in as little as 20 minutes. Food should not sit in it for more than two hours, or one hour above 90°F.

Sous-vide sometimes cooks inside that range on purpose, and that is only defensible when the time at temperature has been calculated to kill what is there. The lowest temperature in the Food Code’s roast table is 130°F. Below that, the published tables stop. Clostridium perfringens, a spore-forming bacterium behind many large outbreaks, can keep multiplying up to about 126°F (52°C), and some strains a little higher. A bath held in the low 120s for hours is an incubator, not a cooker. Settings that low belong to short fish cooks only.

Fish is a different case

Fish cooked sous-vide is often taken to somewhere between 120°F and 130°F for a silky texture. At those temperatures and the short times fish needs, nothing is pasteurized, so the fish should be treated as raw. That means buying fish that is fit to eat raw.

Parasites in fish are handled by freezing. The Food Code requires most fish served raw or undercooked to be frozen at -4°F (-20°C) or below for seven days, or at -31°F (-35°C) until solid and held there for 15 hours. A home freezer set to 0°F is several degrees warmer than the first standard, so freezing at home is no guarantee. Suppliers that sell fish for raw use can say whether it was frozen to that standard. Pregnant people, young children, older adults and anyone with a weakened immune system should skip low-temperature fish and poultry entirely.

After the bath

A vacuum bag is an oxygen-free environment, and that suits Clostridium botulinum. Sous-vide temperatures do not destroy its spores. Some strains found in fish can grow and make toxin at temperatures as low as 38°F (3.3°C), and the food can look and smell normal.

Food that is not eaten straight from the bath should be chilled fast. The Irish factsheet calls for a bath of half ice and half water and for cooling to 41°F (5°C) or below within 150 minutes of the end of cooking, and it advises against putting warm bags straight into the fridge. Once chilled, the bag counts as cooked leftovers: FSIS gives three to four days in a refrigerator at 40°F or below, or three to four months frozen. A sealed bag of cooked meat is not a shelf-stable product, however professional it looks.

Bags should be food grade and rated for the cooking temperature. On long cooks, a separate thermometer in the pot is cheap insurance, since a circulator that fails overnight leaves food in the danger zone for hours.