How Sous Vide Works: The Science of Precise Temperature Cooking

The name means “under vacuum” in French, but that’s almost a distraction from what actually makes sous vide interesting. The vacuum part is minor. The water part is everything.

Why Water Makes Such a Good Cooking Medium

Air is a terrible conductor of heat. Water isn’t. Air holds about 1 joule of heat energy per gram per degree Celsius. Water holds about 4.2 joules. That difference means water can deliver roughly 25 times more heat energy to a food surface than air at the same temperature.

Think of it this way: a 140°F air oven barely feels warm on your hand if you wave it through quickly. A 140°F water bath will scald you in seconds. Same temperature, dramatically different rate of energy transfer. That’s water’s thermal mass at work.

This property does two things for sous vide. First, it heats food faster and more evenly than an oven at the same temperature. Second, it holds the food at an extremely stable temperature, because water doesn’t fluctuate as easily as air does when a door opens or a fan kicks on.

The Precision Problem

Traditional cooking involves a temperature gradient. You set your oven to 425°F to get a steak’s interior to 130°F. The surface hits 350°F+ before the center reaches 80°F. You’re racing to get the interior done before the exterior overcooks.

Sous vide eliminates the gradient. Set the bath to 130°F, and the food will eventually reach 130°F everywhere, then stop. The bath is the ceiling. You can’t cook past it.

This changes what’s possible. Chicken cooked sous vide at 145°F has a creamy, just-set texture that’s impossible to achieve in an oven, because any oven-cooked chicken that’s safe has already gone well past 145°F in many parts of the meat by the time the thickest part reaches a safe temp.

Protein Denaturation at Specific Temperatures

Different proteins in meat denature (unfold and coagulate) at different temperatures. Myosin, the main structural protein in muscle, starts denaturing around 120-130°F. Actin, another muscle protein, denatures around 150-163°F.

When actin denatures, it squeezes water out of the muscle fibers aggressively. That’s why well-done meat is dry. The texture of steak changes dramatically around that 150°F threshold. Sous vide lets you stay precisely below it.

A 130°F water bath keeps meat in the myosin-denatured, actin-intact zone indefinitely. The meat is fully cooked in the sense that proteins have changed structure, but actin hasn’t collapsed and squeezed out moisture. The texture is distinctly different from anything you can achieve with traditional heat. For more on how proteins respond to heat, see protein denaturation.

The Time-Temperature Pasteurization Relationship

Food safety at low temperatures is a common concern with sous vide, and it’s worth understanding the actual science rather than a simplified rule.

Pasteurization is a time-temperature relationship, not a single threshold. It’s based on log reductions of bacterial populations. The USDA’s 165°F rule for poultry means that at 165°F, you get a 7-log reduction (killing 99.99999% of Salmonella) essentially instantly. But you can achieve the same reduction at lower temperatures with more time.

At 140°F, chicken achieves the equivalent pasteurization after about 30 minutes of holding time. At 145°F, it takes about 10 minutes. These are validated by USDA research. Many professional and home cooks use 145°F for 3+ hours for chicken, which is well within the pasteurization envelope with significant time margin.

The key requirement is that the entire food item must reach the target temperature, not just the surface. In a properly controlled sous vide bath with adequate pre-heat time, this is reliably achievable.

Collagen and Low-Slow Temperature Science

Tough cuts of meat are tough because they contain lots of collagen, the structural protein in connective tissue. Collagen has a triple-helix structure that’s mechanically strong at lower temperatures. To get tender braised short ribs, you need to convert that collagen to gelatin.

That conversion happens through hydrolysis: the triple helix unwinds and water molecules break the peptide bonds. It requires both heat and time. The reaction starts meaningfully around 160°F and accelerates at higher temperatures. At 180°F in a traditional braise, it happens in 3-4 hours. See more in collagen to gelatin science.

Sous vide can do this at lower temperatures, but it takes much longer. At 155°F, short ribs in a sous vide bath for 24-36 hours will develop a tender, almost braise-like texture without the overcooked gray color of traditional braising. The collagen conversion happens more slowly, but it happens.

This is one of sous vide’s genuinely unique results: meat that’s cooked to below well-done temperatures but has the tenderness of a long braise. Traditional braising achieves tenderness by cooking well past the actin denaturation point and accepting the moisture loss. Sous vide can reach the same tenderness by sacrificing time instead of temperature.

The Maillard Problem and the Sear Solution

Sous vide has one limitation: it can’t produce the Maillard reaction. The Maillard reaction requires surface temperatures above about 280°F. A 130°F water bath is nowhere near that.

Water also physically prevents browning. Food submerged in water won’t brown because the water keeps the surface temperature capped at whatever the bath temperature is. You need a dry, high-heat surface event to create flavor and crust.

That’s why the sear matters. After sous vide, patting the food completely dry and placing it on a blazing-hot cast iron for 60-90 seconds per side creates the Maillard crust without overcooking the interior you’ve just spent an hour getting exactly right. The interior is already at 130°F, so you have almost no window before it starts overcooking. High heat, bone-dry surface, and speed are all required.

Some cooks also finish sous vide items with a torch, which applies heat even more directly and avoids any carryover from pan contact.

Equipment Basics

A circulator (immersion circulator) is the most common home sous vide tool. It sits in a water container, heats the water, and circulates it to maintain even temperature throughout the bath. Entry-level circulators hold temperature within 0.1-0.2°F. That precision is genuinely useful given how narrow some of the temperature windows are (the difference between 128°F and 133°F chicken is dramatic).

Containers can be anything heat-safe: a stockpot, a cambro, or a dedicated sous vide container. Larger containers have more thermal mass and hold temperature more stably. Insulating the container with a towel or using a lid reduces water evaporation and energy use during long cooks.

The bags don’t need to be vacuum-sealed. A heavy-duty zip-lock bag with air displaced using the water immersion method works well. What matters is that the food is submerged and the bag doesn’t float, which would pull food above the waterline and out of the temperature-controlled bath.