enzyme digests the gelatin molecules and liquifies the jelly But canned pineapple has been heated enough to denature the enzyme, and makes a firm gelatin jelly There’s a complication, though The reactivity of most chemicals increases with increasing temperature The rule of thumb is that reactivity doubles with each rise of 20ºF/10ºC The same tendency goes for enzymes, up to a range in which they begin to denature, become less effective, and finally become completely inactive This means that cooking gives enzymes a chance to do their damage more and more quickly as the temperature rises, and only stops them once they reach their denaturation temperature In general, the best rule is to heat foods as rapidly as possible, thereby minimizing the period during which the enzymes are at their optimum temperatures, and to get them all the way to the boiling point Conversely, desirable enzyme action — meat tenderizing, for example — can be maximized by slow, gradual heating to denaturing temperatures