Technological features of storage for onion sets, mother bulbs, and bulb onions

Onions for various commercial purposes (sets, large sets, mother bulbs, bulb onions) require different storage methods.

Onion sets. Before storage, sets are dried and graded.

Onion sets are graded into three fractions:

Small sets are stored in a cold room. At temperatures from 0 to 15-16°C, onion sets develop flower stalk primordia, so they are stored at -1 to -3°C or at 18-20°C.

Cold-warm storage method: onion sets are heated at 42°C for 8-10 hours for disinfection against downy mildew and stored at 18-20°C. With the onset of cold weather, the sets are quickly cooled to -1 to -3°C. In the spring, they switch back to the warm method: the temperature is raised to +25-35°C for 2-5 days, and then maintained at +10-20°C until planting. Under these conditions, the plants do not bolt and provide the maximum yield of bulb onions.

Onion sets are stored on slatted racks and in crates. In storage facilities with active ventilation, they are poured into bins in a layer of 1.5-2.8 m.

Mother bulbs. To obtain simultaneous shooting and a high seed yield, it is necessary to create conditions for the complete completion of bud differentiation processes in the bulbs, i.e., a low positive temperature of +2-5°C. At this temperature, losses are small and preparation for generative development occurs in a timely manner. At temperatures below 0°C and above +18°C, processes that delay bud differentiation occur.

To accelerate the development of seed plants and increase seed yield, mother bulbs are heated before planting. To do this, for 8-10 days before planting in the field, the temperature in the onion layer is raised to +18-25°C using active ventilation.

Culinary bulb onions of pungent cultivars are stored at a negative temperature (-3 to -1°C) and a relative humidity of air 60-70%. Semi-pungent and sweet cultivars are stored at -1 to +1°C and a humidity of 70-80%. Bulb onions are stored in containers with a capacity of 180-200 kg. Stacks are formed 4-5 tiers high and 2-3 containers wide. Onions also store well in crates with a capacity of 20-25 kg. Before sale, onions must be warmed up to prevent condensation.

Dry heated air is used to ventilate bulb onions, the temperature of which is set depending on the relative humidity of air . With a relative air humidity of 80-85%, the difference between the outdoor temperature and the temperature in the product mass should be 2°C; at 85-90%, it should be -3°C; at 90-95%, -4°C; and above 95%, -5°C.

Large sets weighing more than 10 g are used for forcing green onions.

Large sets for green onion production are stored in a 2 m layer with active ventilation, supplying 100-120 m³/h of air per 1 ton of product at a temperature of +18-22°C and a relative air humidity of 70-80%.

To increase the yield of green onions, a month before planting, the onions are heated at +30°C, increasing the ventilation intensity to 180-200 m³/h.

A bulb that has prepared for the dormancy period is protected from the environment by several layers of dry outer scales, and low air humidity during storage does not cause increased mass loss from evaporation. Therefore, unlike other vegetables, for which high relative air humidity (90-95%) is recommended during storage, onions require air humidity of no more than 75% during storage. At high humidity during storage, onions emerge from the dormancy state faster and begin to sprout. In a humid environment, condensation can occur on the bulbs, the neck becomes damp, and the development of neck rot begins. It is especially important to strictly maintain low air humidity when storing onions that have not fully matured, as they are less resistant to this disease.

Matured onions have the ability to withstand low negative temperatures during storage. A bulb can be frozen to a solid state and, after thawing, does not lose its marketability or even its germinating capacity. Onions should be frozen and thawed gradually. However, the temperature drop that a bulb can withstand has a limit. For well-matured onions, this is -5 to -6°C. With further temperature reduction, ice crystals deform the bulb cells and cause irreversible dehydration of the cytoplasm; therefore, the temperature should not drop below -3°C during onion storage.

After storage in a refrigerator, onions must be warmed gradually, as tissues deform under sudden temperature changes. In addition, cold onions condense moisture in a warm room, and the development of diseases begins.

The most common storage method for dried onions is in bins with active ventilation at a stacking height of 2-3 m. Using this storage method, sets and mother bulbs are stored with natural cooling, while bulb onions for consumption are kept in refrigerators or storage sections with artificial cooling. After reaching the optimal temperature and humidity regime during the main storage period, ventilation of the onion bulk is carried out daily for 1.0-1.5 hours, since continuous fan operation causes cracking of the scales and exposure of the bulbs.

After the storage period ends, commercial processing and packaging of onions into nets are carried out on LRL-400 and LFPL-1500 mechanized lines.

An effective method is storing onions in containers. Matured and well-dried bulb onions for consumption are stored in 180-200 kg containers, stacked in refrigerator chambers. Mother bulbs are stored in 20-25 kg crates, with 20 crates on a standard pallet, forming load units weighing 400-500 kg. Onion sets are placed in trays and stacked to a height of 2 m. Onions store well in thick polyethylene bags with a capacity of 35-40 kg. Open bags are placed vertically on rack pallets, which are stacked in storage chambers in 4-5 tiers.

Garlic storage technologies and regimes

Garlic is more demanding regarding storage conditions than onions. It is prone to self-heating and spoils quickly, so it is important for an agronomist to select the correct regime for each type of produce. Hardneck garlic stores better than softneck, and spring garlic stores better than winter garlic, which has a short dormancy period.

Microclimate parameters are selected depending on the intended use of the garlic. For commercial and seed purposes, temperature and humidity values differ significantly.

• Temperature for consumption garlic — from −1 to −3 °C
• Humidity for consumption garlic — 70–85%
• Temperature for seed garlic — about 0 °C
• Temperature for warm seed storage — 16–20 °C
• Humidity for warm seed storage — 50–70%

For harvesting garlic, the MUCH-1.4 machine is used, and post-harvest processing is carried out on the LDS-3 mechanized line. The processing technology is similar to that used for onions. Garlic is stored in small-capacity crates (up to 25 kg) or in 100–120 kg containers.

Controlled Atmosphere (CA) storage allows for significantly extending the dormancy period and increasing storage life. The optimal composition of the gas mixture is: 3% CO₂, 2% O₂ and 95% N₂.

To prevent drying and reduce mass losses, treating dried bulbs with paraffin is effective. The protective shell prevents water evaporation and protects against pathogens. The consumption of the working mixture is 70–75 kg per 1 ton of garlic.

1. Dry the garlic thoroughly before treatment.
2. Immerse the bulbs for 2–3 seconds in a mixture heated to 70–80 °C (97–98% paraffin and 2–3% monoglyceride, which prevents the coating from cracking).
3. Place the treated garlic into containers or floor bins.
4. Stack the containers in the refrigeration chamber.

Prevention of diseases in vegetable crops during storage

The main barrier to the development of pathogens during the storage of onions and garlic is timely post-harvest drying by warming the produce at 45–46 °C, as well as strict adherence to the temperature and humidity regime.

Violation of storage regulations leads to the development of specific diseases in vegetable crops.

Diseases of headed vegetables:

• Gray mold (causative agent — the fungus Botrytis): heads are covered with gray fluffy mold, leaves become slimy and rot. Develops under conditions of high humidity and elevated temperature in the storage facility.
• White mold (causative agent — the fungus Sclerotinia): heads and cores are covered with a white fluffy coating, tissues soften, and black sclerotia form on them.
• Soft rot (bacteriosis): affected areas turn a brownish hue, soften, and become covered with slime.
• Vascular bacteriosis: leaf petioles and veins become almost black, leaves yellow and dry out.
• Core browning (tumak): occurs due to insufficient oxygen supply to tissues, long-term storage at −2 °C and below, or due to temperature fluctuations.
• Leaf spot necrosis: small, slightly sunken black and gray spots appear on the leaves. It most often affects cabbage grown with an excessive application of nitrogen fertilizers.

Diseases of root crops (carrots and beets):

• White mold (Sclerotinia): root crops are covered with dense white mycelium. The source of infection is soil and plant residues in the field and storage.
• Black rot (Alternaria): sunken dry spots with a gray coating appear on carrots, which then turn into deep ulcers. Actively develops at elevated temperatures; the source of infection is the soil.
• Gray mold: a gray fluffy coating forms on the surface of root crops, tissues turn brown and decompose. Transmitted through contact between root crops and by air currents.
• Bacteriosis: tissues turn black, and grayish-blue spots appear on the surface of carrots and beets.
• Rhizoctonia: a fungal disease in which affected tissues first turn brown and then soften.
• Phoma rot: affects plants during the growing and storage periods. Manifests as dry rot of the upper part of the root crop or as dark transverse spots. Voids with mycelium form inside. Transmitted by seed and plant residues.

Diseases of onion and garlic:

• Neck rot of onion (pathogen — Botrytis fungus): infection occurs in the field, the disease manifests after harvesting. The neck rots, then the entire bulb. The tissues become watery, yellowish-pink, covered with gray mold, and the neck softens.
• Bacteriosis: sunken yellow-pink areas with an unpleasant odor appear on onion scales. Brown stripes or depressions form on garlic cloves, and the tissue turns a pearly yellow color.
• Onion nematode: whitish spots appear on the bulbs, the tissues become loose and granular, and succulent scales separate, forming cavities. The basal plate falls off, the bulb decays, and the bases of the dry scales turn yellow.

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