It is unsatisfactory to fry or deep-fry in oil that isn't hot enough, and since the addition of room-temperature food will surely lower the temperature of a hot oil, it stands to reason that you should not cook too much food at any one time. The less food you add to the oil, the smaller the drop in oil temperature and the quicker the temperature recovery time. When deep-frying, use at least six volumes of oil for each volume of food.

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