Spawn can be stored for only a short period of time before a decline in viability occurs. Those who buy spawn from afar are especially at risk. As spawn ages, and with the depletion of food resources, the mycelium's rate of growth declines. Metabolic wastes accumulate. With the loss of vitality, the mycelium's anti-disease defensive mechanisms fail. Opportunistic molds, bacteria, viruses, and other microscopic organisms proliferate. Good quality spawn on Day 60 (from the date of inoculation) can be half as viable at Day 30.
Generally, spawn should be used at peak vi tality. If it can not, only one option remains: refrigeration. Spawn can be refrigerated for several weeks at 35-40° F. (1.6-4.4° C.), effectively slowiiig its rate of decline, provided the refrigeration process does not in il self, cause contamination to flourish. Spawn must not be
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kept in a refrigerator in the same space as mushrooms are stored. The mushroom spores can become a vehicle of contamination bactena and other fungi directly into the stored spawn. Spoiling mushrooms are often covered with the very contaminants so dreaded in the laboratory environment.
Another problem with refrigeration rooms is that the cooling of spawn causes condensation within the spawn containers. Free water, m the form of condensation, should always be viewed with concern by the cultivator. Contaminants proliferate within the water droplets and are efficiently spread by them. Bacteria, in particular, reproduce feverishly in free water environments, even at cool temperatures. Further, refrigeration blowers and cooling elements at-trac and collect dust particles, which inevitably must be cleaned. The force of the ir blasting from the cooling elements covers the outer surfaces of the bags with contaminant particles that are easily transferred by anyone handling them. Most often, the filter media, designed to limit airborne contamination, become the sites of black and green mold growth. In time, they can penetrate from the outside into the intenor environment of the spawn containers.
If refrigeration is your only alternative, then, by definition, you have missed the best opportunity: to use the spawn at its peak of vitality. Nevertheless, every spawn producerfaces this dilemma. So, if you have to refrigerate your spawn, the following precautions are suggested.
1. Treat the refrigeration room as if it were a clean-room. Analyze all potential contamination vectors. Install a HEPA filter if necessary. Make sure floors and walls are kept clean by frequently washing with a 10% bleach solution.
2. Rotate your spawn! Only similarly aged spawn should be kept together.
3 .When refrigerating spawn, use bags, not jars.
4. Inspect the stored spawn once a week for visible signs of contamination, especially at the location of the microporous filter patches. (Although spores may not pass through the filtration material, mold mycelia can.)
5 Maintain a low relative humidity. The humidity should never exceed 60%, and should ideally be kept in the 40-50% rangt.
6 Minimize any material which could become a platform for mold growth, particularly wood, cardboard, and other paper products.
Lastly, some species are more receptive to cold storage than others. Some of the tropical species die upon exposure to cold temperatures. ('Volvariella volvacea is one notable example.) The cold-weather Oyster strains (Pleurotus ostreatus and allies) can be shocked into fruiting upon placement into a cold room. One commonly sees Oyster mushrooms fruiting frantically in containers which were otherwise hermetically sealed. The force of fruiting, the bursting forth of mushrooms within the spawn containers, can actually cause enough stress to split plastic seams, unscrew lids on bottles, and force apart filter membranes.
With the rapid-cycle spawn techniques described in this book, cold storage of spawn is not necessary and is not recommended. Cold storage is an option widely utilized by the Agarlcus industry, an industry historically fractured into specialty companies When inventories exceed demand, spawn is kept for as long as possible under refrigeration. Often the consumer, not knowing better, becomes the victim of a spawn producer's over-production. If the spawn fails, the excuse heard, more often than not, is that the spawn was mishandled by the purchaser. This type of business relationship is intrinsically problematic, and is yet anc her reason why mushroom farms should generate their own spawn.
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