When is the best time to harvest jujubes?

The ripening period of jujube fruit can be divided into 3 stages: the white-ripe stage, the crisp-ripe stage and the fully ripe stage. When to harvest the fruit should be determined by the intended use of the jujubes.

(1) White-ripe stage: at this stage the green color of the peel fades, turning greenish-white or milky white. The flesh is soft and loose, the juice is scant, and the sugar content is low. For processing candied jujubes, harvesting should be done at the white-ripe stage.

(2) Crisp-ripe stage: from the time the stem cavity and shoulders turn red until the fruit is fully red, the texture becomes crisp, the juice increases, and the sugar content rises sharply. For fresh eating and for processing wine-soaked jujubes, harvesting should be done at this stage.

(3) Fully ripe stage: the red color of the peel deepens and becomes slightly wrinkled, the flesh near the pit turns yellowish-brown, and the texture becomes soft. At this stage the fruit is fully mature. For drying varieties, harvesting at this stage gives a high drying yield, deep color, thick and plump flesh, good elasticity and good quality. How are dried jujubes sun-dried?

In most jujube-producing areas of our country, natural sun-drying is used to dry jujubes. This method is simple and easy to carry out, requires little investment, and handles large volumes. The specific fruit-drying method is as follows: choose a flat, sunny site with no standing water for the drying ground, and use bricks and bamboo strips to raise a sorghum-stalk mat 15 cm above the ground. Spread the jujubes evenly on the mat to a thickness of 6-10 cm and sun them for 3-4 days. During sunning, turn them once every 1 hour. At night, pile the jujubes in the middle of the mat in a ridge shape and cover them well with a mat. After 3-4 days of sunning, spread the jujubes out to dry every morning, pile them up at 11 a.m., and spread them out again after 2 p.m. After drying this way for a period, fine line-like wrinkles appear on the peel and the fruit feels elastic when held in the hand; at this point the jujubes can be piled up together with the mat and sealed tightly with a mat, and every few days uncover the mat to ventilate for 3-4 hours. During the drying process of jujubes, the following issues should be noted:

(1) Because jujubes of different maturity have different moisture contents, the length of drying time needed also differs. Therefore, before drying, the jujubes should be graded according to maturity and dried separately, so that the dried jujubes have consistent dryness and moisture. When grading, pick out insect-damaged, rotten, bruised and diseased fruit.

(2) During sunning, pay attention to turning them frequently. If jujubes are sunned for too long, "oil-head" jujubes are prone to appear.

(3) During the drying period, it is also necessary to continuously sort and grade them according to moisture content, and to dry jujubes with inconsistent moisture content on separate mats.

At present, fresh jujube storage and preservation technology is still not quite up to standard, and they cannot be stored for a long time; generally they can only be kept for 2 months to 3 months. There are many factors affecting the preservation of jujube fruit, such as variety, harvest maturity, type of chemical agent, and storage conditions (such as temperature, humidity and gas composition). (1) Choose corresponding storage-tolerant varieties. Storage-tolerant varieties include Winter Jujube, Xifengshan Xiaozao, Xifengshan Xiaoyazao, Tuanzao, Hamazao, Jianzao, Muzao, October Red and so on.

(2) Timely harvesting: generally, the lower the maturity, the more storage-tolerant the fruit; however, if harvested too early, the sugar content is low, the flavor is poor, nutrient accumulation is low, while respiratory metabolism is vigorous and substrate consumption is high; in addition, the protective tissue on the jujube surface is not fully developed, its water-holding capacity is poor, and it easily loses water. If harvested too late, the fruit has low vitality, poor resistance to adverse external conditions, and poor storage tolerance. Therefore, for fresh-eating varieties, harvesting at the half-red stage is appropriate.

(3) Fruit-picking method: generally pick by hand, pick and place gently, avoid bruising, and take care to keep the fruit stalk intact.

(4) Precooling: generally use water spraying or water immersion to cool the fruit for precooling. The purpose is to avoid bringing a large amount of field heat into the fruit, weaken respiration, and help prolong the storage period.

(5) Chemical treatment: soaking the fruit in calcium chloride or spraying calcium chloride, gibberellin or thiophanate-methyl and other chemicals before harvest can prolong the storage period. Calcium can change the ratio of water-soluble to non-water-soluble pectin in jujube fruit, causing most of the pectin to become non-water-soluble; secondly, calcium fixes on the protoplast surface and at exchange sites of the cell wall, reducing permeability and weakening respiration. Generally, calcium chloride is used at a concentration of 0.2%-2%, soaking for half an hour. However, the effect of chemical treatment is related to variety. For example, when Xifengshan Xiaozao and Pozao were sprayed with 0.2% calcium chloride half a month before harvest, after 45 days of storage, the good-fruit rate of the former increased by 13.8%, while the effect on the latter was not very obvious. Therefore, when applying this, suitable types of chemicals and appropriate concentrations should be selected.

(6) Bagging: to reduce water evaporation and appropriately inhibit respiration, put the fruit into perforated plastic bags or cling-film bags. This can both maintain low temperature and avoid accumulating too much carbon dioxide. Put 2-4 kg of jujube fruit in each bag, seal the bag opening, and place them in layers.

(7) Management during storage: keep the storage warehouse temperature stable at 0±1°C (or slightly above the freezing point temperature of the variety), keep the relative humidity inside the bags stable at 90%-95%, and keep the carbon dioxide concentration below 5%. Also frequently take samples to check changes in the fruit, and take them out of storage early if necessary.