Latest Grape Storage and Fresh-Keeping Techniques Tutorial
Grapes are one of the fruits we commonly see in daily life, with a sweet and tangy taste and a relatively affordable price. However, grapes easily attract insects and mosquitoes, cannot be kept fresh for long, and are not suitable for prolonged storage. During grape harvest season, due to heavy sales pressure, many growers have no choice but 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 be able to effectively store and keep grapes fresh. Grapes do not have a ripening-after-harvest process, so they must be harvested once fully ripe, and unripe grapes do not store well either. Below, Qinnong Web introduces for everyone: grape storage and fresh-keeping techniques.
I. Pre-harvest management must be carried out thoroughly
Increasing the sugar content of grapes enhances their storability. Applying organic fertilizer not only increases yield but also improves quality, sugar content and storability. Applying too much quick-acting nitrogen fertilizer, or over-applying nitrogen fertilizer, especially in the mid-to-late stages, will significantly reduce grape quality, and the grapes will easily rot and deteriorate during storage. To increase yield, sugar content and storability, during the mid-to-late stages of grape growth, one application of decomposed organic manure such as human and animal urine diluted with water may be poured on, at 500-700 kg per mu each time, applied in furrows or holes. From 15-20 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. When harvesting grapes, the 14-13 soft tips (berries) at the lower end of the cluster must be cut off; these berries are small, low in sugar content and prone to rotting, and must be removed.
II. Scientific harvesting and pre-cooling treatment
There are many table grape varieties, and storability differs considerably among varieties. Generally speaking, very early-maturing and early-maturing varieties are mostly not storable, late-maturing varieties mostly have good storability, and the storability of mid-maturing varieties mostly falls between the two. Kyoho, Pearl of Csaba (Bolgars), White Muscat and others have relatively good storability; Milk and Pearl of Csaba (Shaba Pearl) and others are not storable; Muscat Hamburg and others have medium storability. Grapes have no post-ripening nature, 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 sun. Bamboo, wooden or cardboard boxes can be used for transporting grapes, but before use these containers need to be placed in the sun to dry for 1-2 days, then disinfected paper scraps or similar should be laid around the four sides and bottom of the box to prevent sharp parts from damaging the berries. Each box should preferably hold 15-20 kg of grapes; too much or too little is inconvenient for handling. Grapes of different varieties must be harvested and stored/transported 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°C pre-cooling room to cool for 24 hours before storage.
III. Disinfection of the storage site
The storage site and utensils should be carefully cleaned before the grapes are put into storage. Sprinkle a layer of quicklime powder on the ground and spray 20% limewater on the surrounding walls. Then fumigate with 10-15 g of formalin per cubic meter of space in a sealed manner for 6-10 hours. Afterward, open the doors and windows to ventilate and disperse the medicinal odor before putting the grapes into storage.
IV. Storage and fresh-keeping methods
1. Cellar storage. Cellars or air-raid shelters used for storing apples and pears can be slightly reorganized and used to store grapes. Set up wooden or iron racks 100 cm wide with each layer 30-40 cm high inside the cellar, and place the grapes on them. During storage, check once every 15-20 days, promptly removing diseased and rotten berries, and ventilate once every 7-10 days. The suitable temperature for storage by this method is 3-4°C, with relative air humidity of 85%-90%, and it can store 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 rodents and insect pests, a low groundwater table, good airtightness, and fully automatic refrigeration equipment installed. Build 2-3 tiers 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, maintain the room temperature at 0-1°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 a cellar or single-story house, etc., use wood or iron rods to build a rack, and hang the grape clusters on wood or bamboo poles, etc. This method is most suitable for storing late-maturing varieties and cannot be used to store early-maturing varieties. During storage, maintain the temperature at 0-1°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 table, 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 on the bottom, then spray the bottom and both sides of the trench with pesticides such as a 3000-fold dilution of 2.5% deltamethrin emulsifiable concentrate to repel insects and rodents, then gently place the grape clusters on the dry fine river sand, placing a total of 3 layers of fruit clusters. Cover the top with a thin layer of clean straw or newspaper, etc., and finally build an inverted “V”-shaped frame 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°C, cover with straw mats day and night; when the outside temperature drops below 0°C, cover with straw curtains to prevent freezing. The suitable temperature for trench storage is 3-4°C, with relative air humidity of 85%. This method is only suitable for northern production areas and can store for 60-80 days.
5. Cold storage warehouse storage. Stack bamboo or wooden baskets already filled with grapes in the warehouse in a “pin” shape; the stack height should not exceed four baskets, and leave aisles more than 1 m wide between stacks to facilitate operations. Grapes should preferably be stored alone and must not be stored together or mixed with other fruits. Grapes of different varieties and different maturity stages must also be stored separately. The optimal temperature for cold storage warehouse storage is 0-1°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, etc., jars or vats can be used for storage, and the fresh-keeping effect is also quite good. According to the amount of grapes to be stored, choose a jar or vat of suitable size. First wash the jar, etc. clean with clean water, then dry the water with a dry towel, then use a cotton ball dipped in 70% alcohol to wipe the inner wall. After it dries, gently place the grapes layer by layer inside, with each layer 10-15 cm thick, then place a bamboo curtain, and place grapes on the bamboo curtain again, 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 buried deep in a soil pit, covered with 20 cm of soil on top. This method can store and keep fresh for 1-2 months.
The above is the grape storage and fresh-keeping techniques introduced for everyone by Qinnong Web. It can be seen that through these methods, grapes can mostly be stored for 1-2 months, and with cold storage warehouse storage the time can be as long as 4 months. This not only achieves long-term storage of grapes, but also allows growers to bypass the grape harvest season and achieve off-season marketing, increasing growers' income.