What Actually Happens When Mushrooms Are Vacuum Cooled?
For mushroom growers, removing heat from freshly harvested mushrooms as quickly as possible is one of the most important stages of post-harvest handling. The biggest and best growers use the vacuum cooling process for mushrooms.
But what actually happens to a mushroom inside a vacuum cooler?
The answer involves much more than simply lowering its temperature.
Why mushrooms respond so well to vacuum cooling
Fresh mushrooms have a very high moisture content and porous structure. These characteristics make Agaricus bisporusparticularly suitable for evaporative vacuum cooling.
After harvest, mushrooms remain biologically active. Post-harvest development continues, while inadequate temperature control can accelerate changes in firmness, colour, stipe elongation and veil opening.
This makes rapid mushroom vacuum cooling an important first stage in establishing an effective cold chain.
Vacuum Cooling Process for Mushrooms -What happens when chamber pressure falls?
Inside a vacuum cooler, air is removed from the sealed chamber and the absolute pressure progressively decreases.
As pressure falls, so does the boiling point of water.
At sufficiently low pressure, a small proportion of moisture within and around the mushroom begins to evaporate at low temperature.
This phase change from liquid water to water vapour requires latent heat. That energy is taken from the mushroom itself, causing its temperature to fall rapidly.
Unlike conventional air cooling, where heat must transfer from the product into surrounding cold air, vacuum cooling uses controlled evaporation to remove heat from the product.
What happens to the mushroom itself?
A 2023 study published in Microchemical Journal investigated Agaricus bisporus during vacuum cooling.
Researchers monitored moisture content, lightness (L*), yellowness (b*), hardness and chewiness as cooling progressed. The study demonstrated moisture migration and evaporation from both the surface and internal regions of the mushroom during the vacuum cooling process for mushrooms.
Read the scientific study on mushroom vacuum cooling – ScienceDirect
Some moisture loss is therefore inherent in vacuum cooling because evaporation is the mechanism producing the cooling effect.
The objective of a correctly configured system is to achieve the required core temperature rapidly while controlling evaporative weight loss.
Why does rapid pre-cooling matter?
Temperature has a major influence on post-harvest mushroom quality.
Research into button mushroom cooling has shown that cooling conditions can influence subsequent water loss, firmness, colour and browning during refrigerated storage.
Read the research on cooling rate and mushroom quality – ScienceDirect
For growers, rapid pre-cooling can therefore help slow processes associated with:
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Loss of firmness and texture
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Surface discolouration and browning
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Stipe elongation
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Veil opening
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Moisture and weight loss
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General post-harvest deterioration
The objective is to remove product heat quickly and then maintain the required temperature throughout storage, packing and distribution.
What size vacuum cooler does a mushroom farm need?
Commercial mushroom operations vary enormously in production volume, which means vacuum cooling systems need to be matched to throughput rather than simply chamber size.
Cold Change supplies vacuum coolers from single pallet through to 20 pallet systems.
Vacuum cooling is the beginning of the cold chain
Vacuum cooling does not replace refrigerated storage.
Instead, it rapidly removes product heat before cold storage and refrigerated distribution.
For mushroom growers, this is the real value of the process.
It isn’t simply making mushrooms cold.
It is using controlled evaporation under reduced pressure to rapidly remove heat from a highly perishable biological product — helping establish the cold chain earlier and preserve the characteristics growers and customers associate with freshness: colour, firmness, closed caps, short stems and overall marketable quality.
Explore the complete Cold Change vacuum cooler range
With correctly selected equipment capable of approximately 3–4 cycles per hour, systems can be sized for everything from smaller farms using a 2 pallet vacuum chiller to major commercial mushroom operations using 10 pallet, 14 pallet, 16 pallet, 18 pallet or 20 pallet vacuum cooling systems.
Cold Change can assess your:
Pallet weight + mushrooms per pallet + harvest temperature + required final temperature + pallets per hour + operating hours
and recommend an appropriate cooling system.
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