You can store unopened matcha in the fridge or freezer for ages.
odarwin wrote:how about the matcha whisk? how do you guys store yours?
my whisk came with a clear plastic tube. but after the first use, it seems as thou the tines were no longer "curly" as it was when it was still new and unused. it turned out that i can no longer close the lid of the plastic tube container with out forcing the tines down for about 1/4 to 1/2 inch.
There are a couple of options for storage. However you store your whisk, you should wash it well by whisking it in clean water, shake off the excess moisture, and smooth the loose portion of the thread after use. Traditionally, chasen are stored in the preparation area adjacent to the tea room (the mizuya). They are either kept on bamboo pegs (short sticks of bamboo which protrude from the wall above the sink of the mizuya) or simply upright on a slatted shelf above the sink; both allow water to fall away from the whisk and encourage drying. You can also store your whisk on a whisk-reshaper (called a chasen kusenaoshi in Japanese), which are usually either a celadon-coloured ceramic or unfinished pine, and have a rounded cone shape with a flared base. They maintain the shape of the chasen, but not the tightly curled tips of the tines, which will relax from the first use. I would only keep a completely dry whisk in the original plastic box--and keep the little packet of dessicant too. It's perfectly fine to carefully force the tines down with the lid, and this helps to maintain their shape, but be careful not to trap any between the body and lid of the box.
A chasen should always be softened in hot water before use, and should be checked before and after use for broken tines. Just break off any damaged tips: a chasen can be used for whisking tea until it's pretty decrepit (but for a formal tea ceremony one should really use a new one). Really damaged chasen can be repurposed for other things, like beating eggs or, in tea ceremony, for sprinkling water on chabana flower arrangements.
Fun fact: in Japan, you can take your old chasen to be ritually burned at a kind of "thank you" ceremony at temples once per year (they do something similar for sewing needles too).