Make sure they are thoroughly cleaned before use to avoid possible contamination of the solution and fungal growth.
A higher concentration of citric acid solution will store better than a lower concentration solution. A good measure is 1 lb. (454 g) of citric acid powder to 1 pint (470 ml) of water. However, a lower concentration solution of 1 lb. (454 g) of citric acid to 2 pints of water (940 ml) also works, is more economical, and results in the convenient ratio of one fluid ounce (30 ml) of the solution being equivalent to one-half ounce (14 g) of the dry powder. [4] X Research source
Utilizing a microwave-safe container is an option, but always be careful when boiling water in a microwave. It can superheat and then rapidly boil over when disturbed. Check the water frequently and when removing, wear an oven mitt and carefully give the container a nudge to make sure it does not want to boil over. Also place a wooden chopstick or similar item in the water before heating (it will attract the bubbles so they don’t all form at once). [5] X Research source
