Humidity control for fresh produce storage in commercial refrigeration

Why humidity matters

Fresh produce is still alive and still losing water through its skin. The drier the surrounding air, the faster it loses water. A few per cent of weight lost as water is enough to make leaves limp and herbs shrivel. Produce storage guides adapted from the USDA's Agriculture Handbook 66 list a relative humidity of about 90 to 95 per cent for many fruits and vegetables, with notable exceptions such as onions and garlic, which keep better around 65 to 75 per cent.

Too much humidity has its own risk: water condensing on produce encourages mould and bacterial rot. The aim is moist air, not wet produce.

How refrigerators dry the air

A refrigerator removes moisture as well as heat. Warm, moist air passing over the cold evaporator coil drops its water as condensation or frost, which is then drained away. The bigger the difference between the coil temperature and the cabinet air, the more moisture it pulls out. Fan-assisted cabinets that blow air across open trays of produce dry them especially quickly.

General-purpose kitchen refrigerators are designed to hold temperature, not humidity. Specialist produce cold rooms are designed with larger coils and smaller temperature differences so the air stays moist.

Chilling injury: when cold is too cold

Many tropical and subtropical crops are damaged by low temperatures that are well above freezing. FAO material based on Handbook 66 notes that many fruit and vegetable crops are susceptible to chilling injury when cooled below about 13 to 16 °C. Symptoms include pitting, browning, water-soaked patches and failure to ripen, and often appear only after the produce returns to room temperature.

For Indian kitchens and stores this matters: produce like bananas, many mango varieties and some gourds don't belong in a 3 °C refrigerator. Store them in a cool area, or in a separate unit at a warmer setting where your volume justifies it.

Broad storage groups

Practical ways to keep produce fresh

• Use closed or lidded containers, or perforated food-grade bags, to keep humid air around produce while letting some air exchange.
• Dry washed produce before storage; free water on leaves speeds rot.
• Keep produce out of the direct airflow from the fan.
• Store ethylene-producing fruit, such as ripe bananas and some ripening fruit, away from ethylene-sensitive items like leafy greens.
• Don't store produce below raw meat; it should sit above raw food, and ready-to-eat produce needs protecting.
• Monitor humidity with a hygrometer if produce quality matters to your business; extension guidance warns against judging humidity by how produce looks.

Indian conditions: monsoon and summer

In the monsoon, humid air enters with every door opening and moisture condenses on cold produce and cabinet surfaces; mould risk rises, so check stock more often and keep containers dry. In summer, the large difference between hot kitchen air and the cabinet makes the coil work harder and can dry produce faster. In both seasons, short door openings and covered storage help.