Grape Cold Storage Operating Procedure Temperature Humidity and CA
A complete guide to grape cold storage — variety tolerance, optimal temperature ranges, humidity and CA best practices.
- Technical
- March 4, 2024
- 6 min read
Grapes are one of the least forgiving fruits in cold storage. They lose water quickly, they are sensitive to ethylene from neighbouring crops, and the rachis browns long before the berries themselves look unsellable. Getting the room right is the difference between selling at harvest prices and selling six months later.
Variety decides what is possible
Storage behaviour varies significantly by variety. Eastern European varieties are generally more tolerant of long storage; American varieties are less so. Before sizing a room, decide which varieties will actually go into it, because a store designed for a tolerant variety will disappoint on a sensitive one.
Temperature and humidity band
The working band for grapes is minus 1 to 0 degrees Celsius with 85-95% relative humidity. Both halves matter equally. Too warm and respiration continues; too dry and the stems desiccate, which buyers read as age even when the berries are sound.
| Parameter | Target | Why it matters |
|---|---|---|
| Air temperature | -1 to 0 degrees C | Slows respiration without freezing the berry |
| Relative humidity | 85-95% | Prevents stem desiccation and weight loss |
| Ethylene | Scrubbed | Prevents premature ripening |
| CA oxygen | 2-3% | Slows respiration further |
| CA carbon dioxide | 1-3% | Suppresses decay development |
Holding that humidity band is an equipment decision, not an operating one. Coil selection and the temperature difference between air and refrigerant determine how much moisture is pulled out of the room at every pass. A coil selected for a general-purpose chiller will run the room dry.
Ethylene control
Ethylene scrubbing is critical. Grapes stored near ethylene-producing crops ripen prematurely, and in a mixed packhouse that is an easy mistake to make. Either dedicate the room, or scrub.
When controlled atmosphere pays
On top of refrigeration, controlled atmosphere regulates the gas composition of the room: oxygen reduced to 2-3% and carbon dioxide raised to 1-3%. For grapes this can extend shelf life by 3-6 months. Whether that pays depends on the price spread between harvest and out-of-season sale in your market, and on whether your varieties tolerate the extra time.
A CA chamber is still a normal cold room when the gas control is switched off, which is how most packhouses use the space between harvests.
Room design consequences
- Gas-tight envelope construction if CA is planned, decided before the panels are ordered
- Coil and airflow selection for high humidity rather than maximum dehumidification
- Separate pre-cooling capacity so field heat is removed before the holding room
- Logged temperature and humidity history per chamber for buyer assurance
Quick Answers
What temperature should grapes be stored at?
Minus 1 to 0 degrees Celsius, with 85-95% relative humidity.
How much longer does CA storage keep grapes?
Controlled atmosphere with oxygen at 2-3% and carbon dioxide at 1-3% can extend shelf life by 3 to 6 months beyond refrigeration alone.
Why is ethylene scrubbing necessary?
Ethylene accelerates ripening. Without scrubbing, grapes stored alongside ethylene-producing crops ripen prematurely and lose storage life.
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