Water-bath cooking spent years as professional equipment before appearing in domestic kitchens. What moved was not the technique but the price and size of the machine that controls the water.
Doneness is a temperature, not a duration
The changes that make meat firm, then tender, then dry happen as specific proteins unfold and contract, and each of those transitions occurs within a narrow temperature range.
Conventional cooking applies far more heat than the target and relies on the cook removing the food at the right moment before the interior overshoots.
A bath held at the finishing temperature removes that race entirely. The food approaches the target and then stops, because there is no hotter source available to it.
Restaurants adopted it for the service problem
A kitchen sending many covers cannot cook every protein to order from raw within the time a table will wait.
Cooking in advance to an exact internal temperature and holding it there lets the line finish a dish in the minute before it leaves rather than the twenty before.
It also removes cook-to-cook variation on the item most likely to be sent back, which is worth more to a kitchen than any flavour improvement.
The equipment got small and cheap
Early systems were plumbed water baths with their own tanks, costing what a commercial oven cost and taking comparable space.
The immersion circulator moved the heater, pump and controller into a stick that clamps to any pot the cook already owns.
Once the hardware was a single small appliance rather than a fixed installation, the barrier to home use was no longer money or space.
The bag cannot brown anything
The temperatures involved are far below those at which browning occurs, so food leaves the bath cooked through and grey.
Every recipe therefore ends with a hard, brief sear in a very hot pan or over a grill, purely to build the crust and its flavour.
Skipping that step is the most common disappointment, because the technique delivers texture and evenness but contributes no roasted character at all.
It suits a narrow set of ingredients
Vegetables need temperatures near boiling to soften their cell walls, so bath cooking offers them little beyond convenience.
Long holds at warm temperatures also require attention to chilling and storage afterwards, which is a food-safety matter where general guidance varies and specifics are worth checking.
The technique earns its place on thick cuts, eggs and anything where a few degrees separate the result people want from the one they do not.