Ripening

Ripening 

of fruit, the bringing of unripened fruit to consumer ripeness. Fruit can be ripened in warehouses, or storage facilities, or in specially equipped lockers (artificial ripening). The winter varieties of apples and pears, as a rule, do not ripen on the tree. The summer and autumn varieties of apples and pears, as well as apricots, tomatoes, peaches, and melons are often harvested unripe to increase their transport-ability and length of storage. With ripening the fruit acquires its consumer qualities (taste, aroma, and so forth).

Ripening, whether on the plant or not, breaks down the compound organic substances of the fruits in simple ones—for example, protopectin turns into soluble pectin, starch is converted into sugar, and the fruit’s acid content is reduced. As a result, the fruit becomes softer and sweeter. Ripened (on the plant or artificially) fruit acquires its characteristic color as a result of the formation of coloring substances (pigments) in it. However, in fruit that is plant-ripened substances not only break down, but are also synthesized. The taste qualities of such fruit are higher than of fruit ripened in storage. For this reason, immature fruit is harvested and subsequently ripened only when necessary. Tomatoes are almost always artificially ripened.

Undamaged fruit is placed in open, well-ventilated boxes to ripen. Storage facilities are ventilated, heated, and protected from daylight. The speed of the artificial ripening depends upon the air humidity and temperature in the warehouse or locker. The relative air humidity should not be over 80 percent. To slow down ripening, fruit (for example, apples, pears, stone fruits, and melons) is stored at the lowest possible temperature, and to accelerate ripening, at approximately 20°C. At temperatures above 25°C, ripening is also retarded, and the decomposition of certain vitamins begins. In tomatoes the coloring pigment does not form and the fruit .becomes yellow.

Ripening can be accelerated by stimulants—for example, ethylene (a gas). Ethylene ripening of tomatoes is particularly effective, as the green mature fruit can be ripened in five days. In northern regions it is advisable to harvest green tomatoes and to ripen them artificially. This makes it possible to obtain ripe fruit one month earlier than with natural vine ripening. Ethylene ripening is done in airtight lockers kept in heated areas.

Triple-ply plywood lockers can be used for small batches of fruit. The fruit is placed on the shelves of the chambers in two or three layers, and the ethylene is introduced (1 liter of gas per cu m of locker). Large batches of fruit are placed in boxes and ripened in lockers equipped with heat and ventilation. Up to 80 kg of fruit can be placed per sq m of shelf. The lockers are filled with ethylene every 24 hours until the fruit has turned russet, after which the supply of gas is turned off. The fruit may also be ripened in gas-tight lockers filled with oxygen (60-80 percent of the locker’s volume). The lockers are kept at approximately 20°C. The fruit is kept in oxygen for three days, after which it ripens well under ordinary conditions.

REFERENCES

Rakitin, Iu. V. Rukovodstvo po uskoreniiu sozrevaniia pomidorov pri pomoshchi etilena, 2nd ed. Moscow-Leningrad, 1950.
Metlitskii, L. V. Biokhimiia na strazhe urozhaia. Moscow, 1965.

L. V. METLITSKII