Many growers say that their mushrooms, when kept in air tight glass containers, will last for 5+ years. Others recommend using carbon dioxide (CO2) for long term storage, to keep oxidation of psilocybin and psilocin to a minimum.

Since most people don't have a tank of CO2 available, dry ice can be used as the CO2 source. Dry ice is frozen carbon dioxide, so evaporating it at room temperature will produce CO2. It's generally quite inexpensive...somewhere on the order of $3 for 10 lbs.

Some people have mentioned a concern that commercially produced dry ice may leave a small amount of acetone residue when evaporated. Apparently acetone is sometimes used in the production of dry ice. Check with your dry ice source to find out about contaminents...ask if it's safe to use in a beverage you're going to cool.

Assuming you've found a source of contaminant-free dry ice...

1. Take an empty mason jar and put a small piece of dry ice in the bottom. In order to fill the jar with CO2 you'll need a piece about 3 cubic centimeters - about the size of a standard die.
2. Immediately put the mushrooms in on top of the dry ice. As long as your CO2 is pure, it's ok for the mushrooms touch the dry ice. Alternately you could put the mushrooms in a plastic bag inside the jar so they don't touch the dry ice.
3. Set the lid lightly on top without sealing it and wait until the dry ice evaporates. Don't tighten the lid until it has all evaporated or it could explode. The carbon dioxide which is released during the evaporation process is heavier than air, so it will stay in the jar while displacing the air.
4. Once the dry ice is fully evaporated, simply tighten the lid
5. The jar can then be kept at room temperature until it's opened. The point of freezing mushrooms is to try to slow the oxydation process. In this case there is no oxygen present, so freezing will have little effect.