Detailed Explanation of Key Points of Grape Storage and Preservation Technology
Grapes are one of the fruits commonly seen in our daily lives, with a sweet and sour taste and a relatively affordable price. However, grapes are highly susceptible to mosquitoes and insects, cannot be kept fresh for long periods, and are not suitable for prolonged storage. During the grape marketing season, due to heavy sales pressure, many growers have to choose to sell at reduced prices, or even at a loss, in order to reduce spoilage losses. To solve this problem, the most important thing is to effectively store and preserve grapes. Grapes do not have a post-ripening process, so they must be harvested after they are fully ripe, and unripe grapes are also not suitable for storage. Below, Qinnong Web introduces for everyone: grape storage and preservation technology.
I. Pre-harvest Management Must Be Carried Out Solidly
Increasing the sugar content of grapes can enhance their storage tolerance. Applying organic fertilizer not only increases yield but also improves quality, sugar content, and storability. Applying too much quick-acting nitrogen fertilizer, over-applying nitrogen fertilizer, especially applying nitrogen fertilizer in the middle and late stages, will significantly reduce grape quality, and the grapes will be prone to rot and deterioration during storage. To increase yield, sugar content, and storage tolerance, in the middle and late stages of grape growth, one application of decomposed human manure and urine diluted with water or other organic manure can be applied, at 500-700 kg per mu each time by furrow or hole application. From 15 to 20 days before grape harvest, except where drought is severe and irrigation is needed, watering must not be done under any circumstances, otherwise storability will be reduced. At grape harvest, the 14-13 soft tips (berries) at the lower end of the cluster should be cut off; the berries in this part are small, low in sugar content, and prone to rot, so they must be removed.
II. Scientific Harvesting and Pre-cooling Treatment
There are many varieties of table grapes, and storage tolerance varies greatly among different varieties. Generally speaking, extremely early-maturing and early-maturing varieties are mostly not storage-tolerant, late-maturing varieties mostly have good storage tolerance, and the storage tolerance of mid-maturing varieties mostly falls between the two. Kyoho, Baogar, White Muscat, and others have relatively good storage tolerance; Milk, Pearl of Csaba, and others are not storage-tolerant; Muscat Hamburg and others have medium storage tolerance. Grapes have no post-ripening, so to maintain the quality of stored fruit, they should be harvested after full maturity, not too early or too late. The most suitable time for harvesting is on cloudy days, or in the morning after the dew has dried or in the evening; they must not be harvested in rainy weather or under high temperature and strong sunlight. Bamboo, wood, or cardboard boxes can be used for transporting grapes; before use, these utensils need to be placed in the sun to dry for 1-2 days, and then disinfected paper scraps or similar should be laid around the four sides and at the bottom of the box to prevent sharp parts from damaging the berries. It is appropriate to pack 15-20 kg of grapes per box; too much or too little is inconvenient for handling. Grapes of different varieties must be harvested and stored separately, and must not be harvested, packed, or stored mixed together. Fruit scissors should be used for harvesting, with light picking, light placing, light packing, light transporting, and light unloading; do not pull forcefully or throw and place carelessly. After harvesting, the grapes should be spread out in a cool, ventilated place for pre-cooling treatment for 1-2 days; it is best to place them in a 0-1 degrees C pre-cooling room for 24 hours of cooling treatment before storage.
III. Disinfection of the Storage Site
The storage site and utensils should be carefully cleaned before the grapes are placed in storage, and a layer of quicklime powder should be scattered on the ground, with 20% quicklime water sprayed on the surrounding walls. Then, for each cubic meter of space, 10-15 grams of formalin should be used for sealed fumigation for 6-10 hours. Afterward, open the doors and windows to ventilate and disperse the medicinal smell, and then the grapes can be placed in storage.
IV. Storage and Preservation Methods ⟧11. Cellar storage. Cellars or air-raid shelters used for storing apples and pears can be slightly organized and then used to store grapes. Set up wooden or iron racks in the cellar with a width of 100 cm and each layer 30-40 cm high, and place the grapes on them. During storage, check once every 15-20 days, promptly remove diseased and rotten berries, and ventilate once every 7-10 days. The suitable temperature for storage by this method is 3-4 degrees C, with relative air humidity of 85%-90%, and it can store for 70-100 days.
1. Cellar storage. A cellar or air-raid shelter used for storing apples and pears can be used to store grapes with only minor adjustments. Set up wooden or iron racks 100 cm wide with each tier 30-40 cm high inside the cellar, and simply place the grapes on them. During storage, check every 15-20 days and promptly remove diseased and rotten berries, and ventilate once every 7-10 days. The suitable temperature for storage by this method is 3-4°C with a relative air humidity of 85%-90%, and the grapes can be stored for 70-100 days.
2. Ordinary single-story house storage. The storage room is required to be on high ground, sheltered from wind and cool, with no or very few rodent and insect pests, a low groundwater level, good airtightness, and it needs to be equipped with fully automatic refrigeration equipment. Build 2-3 layers of wooden or iron racks indoors, gently place the grape clusters on the racks, and cover the top with disinfected paper. Boxes or baskets filled with fruit can also be placed on the racks. During storage, keep the room temperature at 0-1 degrees C and relative air humidity at 85%-90%, and check and ventilate once every 7-10 days. This method can store for 2-3 months.
3. Hanging storage. In cellars or single-story houses, use wood or iron rods to build racks, and hang the grape clusters on wood or bamboo poles. This method is most suitable for storing late-maturing varieties and must not be used to store early-maturing varieties. During storage, keep the temperature at 0-1 degrees C and relative air humidity at 85%-90%, and ventilate once every 7-10 days. This method can store for 2-3 months.
4. Trench storage. The selected site should have high ground, a low groundwater level, solid soil, no rodents or insects, shelter from wind, coolness, and short or no sunlight exposure. The trench runs north-south, with a top width of 1 m, a bottom width of 30-40 cm, and a depth of 80 cm. After the trench is dug, spread 7-10 cm of dry fine river sand at the bottom, then spray the bottom and both sides of the trench with 2.5% deltamethrin emulsifiable concentrate at 3000 times dilution or other pesticides to repel insects, rodents, and so on. Then gently place the grape clusters on the dry fine river sand, placing a total of 3 layers of clusters, cover the top with a thin layer of clean rice straw or newspaper, and finally build an inverted V-shaped support over the trench, covering it with straw mats during the day and uncovering them at night. When the outside daytime temperature drops to 1-2 degrees C, cover with straw mats both day and night; when the outside temperature drops below 0 degrees C, cover with straw curtains to prevent freezing. The suitable temperature for trench storage is 3-4 degrees C, and the relative air humidity is 85%. This method is only suitable for northern production areas and can store for 60-80 days.
5. Cold storage. Stack bamboo or wooden baskets already filled with grapes in the warehouse in a pinwheel shape; the stack height should not exceed four baskets, and aisles more than 1 m wide should be left between stacks to facilitate operations. Grapes should preferably be stored alone and must not be stored together or mixed with other fruits. Different grape varieties and grapes at different maturity stages should also be stored separately. The optimal temperature for cold storage is 0-1 degrees C, with relative air humidity of 90%-95%, and during storage it should be ventilated once every 7-10 days. This method can store for 3-4 months.
6. Simple household storage. When the quantity of grapes is small or a small amount is purchased for fresh eating during the New Year and similar occasions, jars or vats can be used for storage, and the preservation effect is also quite good. According to the amount of grapes to be stored, choose a jar or vat of suitable size. Beforehand, wash the jar and so on clean with clean water, then wipe the water dry with a dry towel, then use a cotton ball dipped in 70% alcohol to wipe the inner wall, and after drying, gently place the grapes in it layer by layer, with each layer 10-15 cm thick. Then place a bamboo curtain, and again place grapes on the bamboo curtain until the jar is full. Finally, tightly seal the opening with non-toxic plastic film and place the jar in a cool place without light. For storing grapes in a smaller-mouthed earthen jar, the jar with its opening tightly sealed with non-toxic plastic film can be deeply buried in a soil pit and covered with 20 cm of soil. This method can store and preserve for 1-2 months.
The above is the grape storage and preservation technology introduced by Qinnong Web. It can be seen that through these methods, most grapes can be stored for 1-2 months, and with cold storage the time can be as long as 4 months. This not only achieves long-term storage of grapes but also allows bypassing the grape marketing season to achieve off-season marketing and increase growers' returns.