Pickling food sous vide is particularly good as the flavour of the pickle is much more quickly absorbed by the food and the quantity of pickle liquid needed is much less than in conventional methods. You don't actually need to use a water bath – instead, it's the power of vacuum-sealing which allows the pickling liquid to force itself into whatever you're looking to pickle, reducing waiting time massively. Mackerel lends itself particularly well to pickling as the flavour of the fish is strong enough to stand up to that of the vinegar and any other complementary flavours that may be added.