The Book of Household Management by Mrs. Beeton

548. THESE INTERESTING FACTS, discovered in the laboratory, throw a

flood of light upon the mysteries of the kitchen. The fibres of meat are surrounded by a liquid which contains albumen in its soluble state, just as it exists in the unboiled egg. During the operation of boiling or roasting, this substance coagulates, and thereby prevents the contraction and hardening of the fibres. The tenderness of well-cooked meat is consequently proportioned to the amount of albumen deposited in its substance. Meat is underdone when it has been heated throughout only to the temperature of coagulating albumen: it is thoroughly done when it has been heated through its whole mass to the temperature at which the colouring matter of the blood coagulates: it is overdone when the heat has been continued long enough to harden the fibres.