PRE-COOLING METHODS FOR VEGETABLES IN PACKING HOUSES

Home-grown and imported vegetables are repacked by farmers, importers, and distribution centres before being delivered to retailers.

These highly perishable vegetables require proper handling and good cold chain management, so that they stay fresh and wholesome. Pre-cooling is an essential step along the cold chain – it rapidly reduces the temperature of vegetables to an optimum of 2-6˚C. Here are the most common types of pre-cooling methods that help to keep vegetables fresh and minimise wastage due to deterioration.


ROOM COOLING

Cool air is circulated by convection.

Suitable Vegetables
All fruited vegetables and fruits

Advantages

  • Clean and simple
  • Low installation & maintenance cost
  • Provides temporary storage after pre-cooling

Disadvantages

  • Slow
  • Uneven cooling at the beginning
  • Not suitable for leafy vegetables due to prolonged cooling hours, resulting in dehydration

VACUUM COOLING

At reduced atmospheric pressure within the vacuum chamber, water rapidly evaporates from the produce’s surface, removing heat in the process.

Suitable Vegetables
Leafy vegetables and mushrooms

Advantages

  • Rapid
  • Uniform cooling for all vegetables
  • High energy efficiency

Disadvantages

  • Risk of wilting due to moisture loss
  • High Cost
  • Requires packaging with holes for water evaporation

FORCED AIR COOLING

Cold air is drawn and forced through crates of vegetables covered by a canvas sheet.

Suitable Vegetables
All leafy, fruited and rooted vegetables

Advantages

  • Clean and simple
  • Rapid
  • High heat transfer performance
  • Low installation & maintenance cost

Disadvantages

  • Slower as compared to vacuum cooling

HYDRO COOLING

Vegetables are showered with or submerged in cold water that is circulated through the heat exchanger.

Suitable Vegetables
Fruited vegetables and fresh fruits tolerant of prolonged exposure to wet conditions

Advantages

  • Rapid
  • High energy efficiency
  • Provide means to clean vegetables (e.g. with chlorinated water) to prevent spoilage

Disadvantages

  • Additional step of drying required
  • Additional effort required to monitor water quality and cleanliness of cooler daily

ICE COOLING

Layers of crushed ice are added on top of the vegetables.

Suitable Vegetables
Broccoli, carrots, Chinese cabbage, green onions, and commodities that have a high respiration rate

Advantages

  • Rapid
  • High heat transfer performance
  • Prevents any moisture loss from vegetables

Disadvantages

  • Additional weight (from crushed ice and high water content from melting ice) could increase the risk of physical injury and rotting of vegetables
  • Risk of chilling injury to vegetables if period of icing is prolonged

OTHER PRE-COOLING TIPS TO TAKE NOTE OF

  • Do not load pre-cooling facility beyond its optimum capacity.
  • When stacking produce, allow adequate air-circulation to ensure all vegetables can be evenly cooled.
  • Use proper receptacles (such as vented boxes and baskets for forced-air cooling, and waxed cartons or Styrofoam boxes for hydro-cooling).
  • Transfer vegetables out from the pre-cooling facility immediately after pre-cooling, to avoid overcooling or dehydration of the vegetables.
  • Use potable water for precoolers to minimise any food safety concerns.
  • Separate ethylene-sensitive vegetables from ethyleneproducing ones.
  • If a chiller is used for precooling, keep it closed at all times to minimise temperature and relative humidity fluctuations.
Extracted from Good Handling Practices in Packing House for Vegetables, published by AVA. Download the complete copy for free here
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What's Next

For the Freshest Produce, Go Local

Did you know that farms in Singapore produce a variety of leafy green vegetables?

She Helps Farmers to Grow

For AVA scientist Fadhlina Suhaimi, job satisfaction comes from helping vegetable farmers improve their livelihood, thereby enhancing Singapore’s food supply resilience.

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