A specialty of southwest France, confit is steeped in tradition. It was developed for very practical purposes – preserving meat before the advent of refrigeration. The preserving aspect is no longer relevant, but confits are still prepared for their succulence and flavours.
Harold McGee describes how intertwined foods and preparations can be. He suggests that confit arose in parallel with foie gras because geese and ducks were being force-fed, not for their livers, but rather to supply the volumes of fat needed to make confit. Foie gras was serendipitous. In turn, force-feeding had become economical because of advances in agriculture (mostly maize). Prior to this, food was preserved salted.
In a traditional duck (leg) confit, the meat was rubbed in a salt-spice mixture blended with potassium nitrate (saltpeter) and left for a day. This was a curing step, and essential for preservation.
The duck was then washed, dried and covered in a rendered fat of choice (e.g. duck fat).
It was then slow-cooked (a day) in an oven set to a low temperature. Typically, the duck itself would be at around 80-90C.
For readers already familiar with sous vide, the parallels are striking. Confit could well be the sous vide we did before we did sous vide.
The duck was then removed from the fat and any surface moisture/gel removed. It was salted a second time and covered in fat for storage.
For eating, the duck needed to be washed to remove excess salt, and sometimes even soaked to reduce salt levels further. It could be fried briefly in fat to crisp. The meat was tender but fibrous. It remained salty, and was often shredded and combined with other flavourings and fat (e.g. for rillettes) to reduce the perception of salt.
The modern approach simplifies all this because preservation is not the aim (salting levels can be reduced to a palatable level) and because the duck can be cooked more simply sous vide for the same (or a better) outcome.
Nathan Myhrvold maintains that in blinded controlled tests, tasters cannot distinguish sous vide-confit from traditional fat-confit. This makes sense, because confit is a method, and not to be confused with a result.
The sous vide method is to flavour the meat in a salt-spice mix of choice, but with only a brining-level of salt (say, 20% by weight of meat for a 6h brine – it is a surface treatment that will be washed off).
The post-brined duck is washed, dried and cooked sous vide. Temperatures: 80C for 4-8h will give a result comparable to fat-confit and best suited to rillettes; 60C for 24-48h yields a more succulent texture with greater serving possibilities.
Once cooked, the meat is wiped dry and brushed lightly with fat while still warm. This is equivalent to a fat-confit because (fortunately) fat does not enter meat when it is cooked directly in fat. Some (very little) fat can enter as the meat cools, but it won’t penetrate more than ~1mm. So brushing the sous vide meat in a little fat after cooking achieves the same thing.
With the fat-confit method, the fat can oxidise a little (a slightly rancid flavour is considered appealing by some), in which case brush the sous vide-confit with a little oxidized fat, or leave it exposed to air for a while.
It may taste the same, but it’s not the same you say. The modernist approach to cooking can sometimes mean sacrificing mystique (breathing red wine in a blender for example).
It is the food that matters in the end. Sous vide-confit creates possibilities (60C confit texture for example) and makes a traditionally complex (and messy) process practical for a home cook.