May a fleishig sous vide machine be used with fish? If so, can I cook fish and meat in the machine at the same time?

Some have the custom, in accordance with the position of the Tur, to keep separate pots and utensils for meat and fish. One who follows this custom should have separate machines for fish and meat as well. However, the more common custom, cited by the Taz (YD 116:2), is to permit using the same utensils for fish and meat, so long as they are clean.

The question arises whether one is permitted to cook meat and fish, each sealed in plastic, in a sous vide at the same time. It would seem that there is a basis to permit this as well. Rav Belsky, zt”l held that one may eat an onion cut with a fleishig knife together with fish. Although an onion cut with a fleishig knife is considered to be fleishig, it is still not actual meat. The sakana (danger) of eating fish and meat together only applies if one mixes actual meat with fish. Although fish cooked at the same time as meat in a separate pouch would be considered fleishig, it is not actual meat. Nonetheless, since the plastic bags may leak, it is not recommended to cook meat and fish simultaneously. If one changes the water between uses, one may cook fish after meat.

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