Sous vide, (French for "under vacuum") for those three food lovers left in the world who don't already know, is a method of cooking vacuum-packed food in a plastic pouch at a set temperature usually in a water bath. It's claimed that it seals in flavours and juices but, perhaps more importantly it allows precise control of the core temperature of the food without any risk of over- or under-cooking. It also gets some food aficionados very hot under the collar.
McGee, Myrvhold, Barham or This explain the science much better than I could, but I'll take a wild swing at it using beef as an example.
If you take a piece of meat, say some fillet steak, and throw it into a hot pan, you heat the exterior very rapidly while the centre takes longer to cook. There are all sorts of variables. The thickness, texture and storage temperature of the meat, the heat of the pan, air temperature; all affect the cooking time. At the end, the surface should be charred, the centre barely cooked and, after a period of resting, the temperature will have evened out through the meat before it gets cold.
Cooking a steak sous-vide is different. Sealed in a watertight pouch it is sunk into water at 56.6C where it remains for a half an hour or so, at which point the core of the meat is at the same temperature as the surrounding water. It doesn't matter much past this point how long the pouch stays in the tank - it simply can't overcook. When the chef needs a steak a pouch is whipped out of the tank, the steak is removed, seasoned and thrown either into a hot pan or under one of those achingly fashionable 400C grills to sear the outside. Without the need for it to be rested, the meat is plated and served.
The physics are laughably simple. We cook things by raising their temperature. Air, by which heat is transmitted in a normal oven, is a lousy conductor. Water or oil are much better - which is why we boil, deep fry or confit some food. Controlling temperature accurately in a box of air - basically what a domestic oven is - is difficult. In a bath of water it's easy. So easy, in fact, that I've put together a photo how-to over here that shows you how to sous vide with equipment you might already have at home. I urge anyone to give it a crack, if only in a spirit of experimentation. It demonstrates the process admirably. It doesn't require anything more complex than a decent thermometer, a beer cooler and water from the hot tap.
That's it, really. All there is to it.
The thing is, sous-vide raises hackles wherever it is mentioned. Either it's the most exciting thing in cookery since fire or it's an appalling, filthy industrial process that debases the chef's art. So why does it bug people so much? Why the ferocious rows?
Sous vide has been around since 1799 - it's exactly the same process (using a jar or can instead of pouch) as canning tuna, that oh-so-authentic French cassoulet or fish soup that we cheerfully pay a fortune for in the deli. If you've eaten in a gastropub or a chain restaurant at any time in the last decade you've almost certainly tried it as sous vide has been favoured for decades in mass-catering as a way of ensuring safe reheating of prepared foods and guaranteeing hygienic handling.
Perhaps it's the latter association that gets backs up, a recollection of Nan's boil-in-the bag cod in parsley sauce. Perhaps it's the fact that any discussion of sous-vide is presented in terms of evangelistic, blokeish geekery. Whichever, it seems a shame to write the process off entirely.
If I'm honest I'm still torn on this one. Part of me feels that as long as there's someone out the back in a white jacket, I'd like to be sure they're good enough at their job to cook a steak properly. But then there's the other side of this, the much bigger utilitarian argument. Sous vide means there's no excuse for anyone to serve an improperly cooked steak ever again. Is not a world of perfect steaks the greatest good for the greatest number of people?
guardian.co.uk © Guardian News and Media 2012