Food preservation includes food processing practices which prevent the growth of microorganisms, such as yeasts (although some methods work by introducing benign bacteria or fungi to the food), and slow the oxidation of fats that cause rancidity. Food preservation may also include processes that inhibit visual deterioration, such as the enzymatic browning reaction in apples after they are cut during food preparation. By preserving food, human communities are able to increase their food security through food storage and reduce food waste, thus increasing the resilience of local food systems and reducing their environmental impact of food production.