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All dry powders should be stored in a cool, dry place as you would store your normal cooking ingredients. As long as they are kept dry, they will be safe from microbial contamination.
As the ingredients age, their functionality or activity may decrease although they are still safe to use. It means you may need to use a little more to get the same effect.
Ingredients should not be stored beyond 5 years of purchase date for this reason. This includes pectin, xanthan, carrageenan, egg yolk powder, alginate, cocoa and Ultratex starch.
In the case of egg yolk powder, it should be frozen for best storage as it contains lipids. It may develop off-flavours as it ages due to lipid oxidation.
If in doubt, substitute fresh egg yolk liquid but use twice the weight.
The other powders provided in the kits should not degrade but keep them dry, especially the calcium chloride which absorbs moisture readily if left open to the air.
The PGPR liquid should not be stored beyond 5 years and will be better to be kept in a refrigerator, again owing to a decrease in its functional activity.