Grapes are the oldest fruit known to man. The Spanish are credited with the introduction of grapes to America over 300 years ago.
Grapes are grown in the temperate zones around the world including Africa, Asia, Australia, Europe, North America and South America.
California is the United States’ major grape producer.
The majority of Northern Hemisphere harvesting occurs in late August to early October. The majority of Southern Hemisphere harvesting occurs between the months of February and April.
When grapes are harvested, the fruit temperature can be anywhere from 71°F to 98°F. Proper storage temperature is 0°F to 1°F.
The faster grapes are cooled from harvest temperatures to the proper temperature, the longer their shelf life, and the less their water loss (water loss also causes stem rot.)
Special rooms known as forced-air pre-coolers are used for rapid cooling of grapes. Most of these quick cooling tunnels are able to cool 10 or 12 pallets of grapes from 95°F to 36°F in 6 hours or less. Each pallet weighs about 2,00o pounds, so that is 20,000 or 24,000 pounds of grapes at a time.
Ironically, forced-air pre-cooling can also itself cause moisture loss, so “Ultra High Humidity PreCoolers” are often used.
Another important factor in extending grape shelf life, is cooling delays from time of cutting to entering the precooler.
Harvest crews might not be able to accumulate a 10 or 12 pallet lot of fruit, for 3 hours or more, so the first-cut fruit is older – by hours – than the last cut fruit. When a full load of grapes has been collected, there is the factor of transportation time to the packhouse, where the precoolers are located. There could also be a queue of fruit ahead, causing a waiting time to enter the precooler.
Early morning harvested grapes are cooler than afternoon harvested grapes, and this fruit is the ideal candidate for extended shelf life, preserving taste and eating quality for up to 2 months.
When grapes are stored in your home refrigerator, they will not last as long as in commercial cold storage, because your fridge runs at about 40°F, far above the ideal holding temperatures for the fruit.
Also, grapes can be harmed by airborne ethylene, mold, and mildew. Many commercial cold storages now have ethylene scrubbers, which purify the air, and further contribute to extended shelf life and eating quality.
Humidifiers are also used to maintain relative humidity above 90%, which also helps. Ultrasonic humidifiers are by far the most popular type, because of the extremely fine water droplet size they produce – 1 micron – which prevents water spotting or damage to the cardboard boxes.