Shrinkage is the reduction in size of baked goods or roast meat and poultry during cooking, caused mainly by loss of water as juices evaporate and drip away, and by proteins contracting with heat. It is generally less when the item is cooked at a low temperature, since gentle heat drives off less moisture and tightens proteins less aggressively. Bakers allow for the slight pull-back of pastry and bread; roasters accept that a joint loses a tenth or more of its weight, which is why resting matters, letting fibres relax and reabsorb juices. Excessive shrinkage signals overcooking or too fierce a heat. For caterers it is also money: yield after cooking decides the true cost per portion.