Maturity indices are used to determine the optimal time to harvest temperate fruits. There are two main types of maturity: horticultural maturity, when the fruit is suitable for the consumer's intended use, and physiological maturity, when maximum growth is reached. Maturity is measured by factors like peel and pulp color, size, shape, firmness, sugar and acid content. Specific fruits like apples are judged by color, flesh firmness, ease of separation from the stem, and starch content. Pears are harvested unripe and judged by firmness, soluble solids, size and skin color. Plums are ready when the skin color changes and reaches a certain firmness level.