Is preparing meat sous-vide on shabbos muttar?
Sous-vide means vacuum packed, sous-vide cooking is when food is vacuum packed and cooked at a controlled temperature between 130oF– 140 oF, for much longer than regular cooking at higher temperatures. Some people prefer cooking this way because the inside and outside cook evenly. Regarding hilchos Shabbos and bishul, although the heat of the cooker is cooler than regular cooking, nevertheless since the meat is now being processed by the fire and the water is heated above yos soledes bo, it is considered cooking and not allowed on shabbos. The definition of mileches bishul is anytime a fire is going effect an item and process it and make it better it is included in meleches bishul.
Rambam Hil. Shabbos 9, M”B 318-1.