Frequently Asked Questions
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Practices -- Cooking
Why won't tomato sauce thicken?
If tomato sauces like ketchup, tomato sauce or tomato puree has not thickened sufficiently after several hours of cooking, one explanation is that it is being cooked with the lid on.
If that isn't the case, then turn the heat up until the sauce is steaming to indicate water evaporation. Stir frequently to prevent scorching. And, as the sauce thickens, protect your hands and arms since it has a tendency to spatter and skin burns may result.