As fruit ripens it absorbs more and more oxygen, and the tannin and vegetable acids which it originally contained are altered, so that it becomes less astringent and acid. The starch is more or less completely turned into levulose or glucose, and soluble pectin is formed. The aroma and taste of ripe fruits depend upon the relative quantity of these different substances, together with various volatile ethers and oils. The sour fruits have either more acid or less sugar, and in the sweet fruits there is a preponderance of sugar which masks the acid taste. The more luscious the fruit, the more soluble sugars and special flavouring substances does it contain.

The employment of fruits as a common article of daily diet is highly beneficial, and the improvements which have been made of late years in methods of culture and means of rapid transportation make some varieties of fresh ripe fruits, such as the orange and the banana, available in almost every climate in all seasons, while their increasing cheapness places them within reach of the poor.