What are the citrus storage methods? The latest practical guide

In recent years, with the development of citrus production and increasingly fierce market competition, post-harvest storage, preservation and commercial handling have become an important part of improving the commercial quality and economic benefits of citrus fruit. Let's take a look below at what citrus storage methods there are!

Cellar storage

Cellar storage is a commonly used method for storing sweet oranges. The method is simple and easy to carry out, with low cost, and is suitable for fruit growers to store fruit in a decentralized way. The humidity inside the cellar is generally 95%-98%, and the temperature is stable at around 12-18°C. The carbon dioxide concentration in the air inside the cellar is very high, reaching 4%-6%. Such a storage environment is very conducive to maintaining the moisture of the fruit, keeping the stored fruit fresh and plump, with a low natural weight loss rate. The storage period can last until May-July of the following year.

Cellars are generally built inside or outside houses on high ground with a low groundwater level. The Nanchong cellar is built as a “triangular cellar” that is narrow at the top and wide at the bottom. The upper opening of the cellar is about 50 cm in diameter, the bottom diameter is generally 2-2.5 m, and the cellar depth is about 1.8 m. The cellar opening is covered with a 3-5 cm thick stone slab. Generally, the lid is opened every 7-10 days for ventilation, and rotten fruit is picked out.

Ventilated warehouse storage

Ventilated warehouse storage belongs to the category of room-temperature storage and is currently the most commonly used method for storing citrus in various parts of the south. Ventilated storage warehouses have the advantages of holding a large amount of fruit, being convenient to operate, and having relatively low construction cost, and are suitable for large-scale commercial storage.

1. Preparation work before entering the warehouse: disinfect the warehouse 15 days before loading. A commonly used disinfection method is fumigation with sulfur. The amount of sulfur used is 109/m3. Grind the sulfur into powder and mix in a little sawdust, divide it into several piles according to the size of the warehouse, and fumigate with the warehouse closed; or spray with a 1% formalin solution, seal for 24 h, then ventilate for 2-3 days until there is completely no medicinal smell in the warehouse, then close the door for later use.

2. Storage management: carry out ventilation management according to changes in temperature and humidity inside and outside the warehouse. When the outside temperature is relatively high, it is advisable to ventilate at night to lower the warehouse temperature. When the outside temperature approaches 0°C, the ventilation windows should be closed to prevent the citrus from freezing, and ventilation should only be carried out at noon on sunny days. If it is continuously cloudy and rainy outside and the humidity outside the warehouse is too high, ventilation is not advisable. The focus of storage management work differs in different storage periods.

① Initial storage period: generally in late November, when the temperature is relatively high, the fruit respires vigorously, producing a large amount of respiratory heat and causing the warehouse temperature to rise. At this time, the main measure is to lower the temperature inside the warehouse. Except on rainy and foggy days, the ventilation equipment of the storage warehouse must be opened every day and night to strengthen ventilation and heat dissipation.

② Mid-storage period: generally from December to around the Spring Festival of the following year. At this time, the temperature is at its lowest of the whole year, so attention should be paid to cold protection and warmth retention. Generally, ventilation is carried out at noon on sunny days every 3-4 days.

③ Late storage period: after the Spring Festival, the temperature gradually rises, the temperature inside the warehouse begins to rise gradually, and the fruit rot rate increases. At this time, the main focus should again be lowering the temperature. On sunny nights, open the ventilation equipment to bring in the cold night air. During the day, close the ventilation equipment to regulate the temperature inside the warehouse so as to maintain it below 10°C as much as possible. In this stage, fruit rot intensifies, so inspection should be strengthened, and rotten fruit, brown spot fruit, and dried-stem fruit should be picked out in time. This has a good effect on reducing stem-end rot and granulation disorders in the late storage period.

Ventilated warehouse storage commonly has the problem of relatively low humidity. Generally, the relative humidity inside the warehouse is around 80%-85%, so the fruit is prone to wilting and relatively high weight loss. Generally, sweet oranges stored for 5 months lose 15%-20% of their weight; mandarin-type fruits stored for 2 months lose 5%-10%. Using plastic film to wrap fruit for storage can increase the relative humidity around the fruit and is an effective measure to reduce weight loss during ventilated storage.

Spontaneous modified atmosphere storage

China began researching the use of plastic film sealed storage methods for citrus storage 30 years ago. First place the citrus in a plastic film tent (bag), then place it in ordinary houses, ventilated storage warehouses, earthen cave dwellings, and other storage sites. Plastic film tents generally use film with a thickness of 0.2-0.25 mm, pressed into large rectangular tents, with the volume determined according to the storage amount, generally 500-1000 kg. Because the suitable carbon dioxide concentration for citrus fruit storage is 2%-4%, in order to prevent carbon dioxide injury, slaked lime is usually scattered into the gaps at the bottom of the tent to absorb carbon dioxide, or the tent door is opened regularly for ventilation.

Spontaneous modified atmosphere storage can also use plastic film bags to package citrus, then tie the bag openings tightly to achieve the modified atmosphere effect. The film bags are mostly made of relatively thin polyethylene film, and the gas composition inside the bag automatically reaches an equilibrium concentration through the respiration of the product itself and the permeability of the film itself.

Mechanical refrigeration

Mechanical refrigeration warehouses can strictly control the temperature, humidity, and ventilation inside the warehouse through manual adjustment, and can significantly extend the storage period of citrus and effectively maintain the freshness of the fruit. The key to low-temperature storage management is controlling suitable low temperature and humidity, and paying attention to ventilation.

When citrus is stored for 4 months under suitable temperature and humidity, the flavor is normal, and the contents of soluble solids, acids, and vitamin C show no obvious changes. It should be noted that citrus fruits cannot tolerate excessively low temperatures and are prone to low-temperature injury. During cold storage, a suitable low temperature needs to be selected according to the characteristics of different types and varieties. Sweet oranges are generally 1-3°C, while loose-skin mandarins have poorer tolerance to low temperature and should generally be controlled above 7-12°C. When storing citrus in mechanical cold storage, attention should also be paid to daily ventilation, supplementing oxygen, and removing excess carbon dioxide, usually keeping carbon dioxide no higher than 1% and oxygen no lower than 17%.

Citrus preservation methods

1. Garlic liquid for preserving citrus: take 1 part garlic cloves, mash them into a paste, put them into 10 parts boiling water, stir, and take the liquid. Cool to room temperature, then soak selected citrus in the garlic liquid. After 10 minutes, take them out and dry them, then store them in boxes or plastic bags. They can be kept fresh for 3 months.

2. Soda water for preserving citrus: dilute and stir 2 parts soda and 1 part water into a liquid, put in the citrus and soak for 2 minutes, take them out and dry them, put them into plastic bags, and tie the bag openings tightly. This can keep citrus fresh for 3 months.