according to
http://www.kavabyrex.com/faqs.html
"
Q: What is the best way to store my kava and how long will it stay fresh?
A: Kava powder should be kept in dry storage conditions. This means cool, dark, dry and in an airtight container.
Similar to where you would keep your tubers, root vegetables and grain. It will last for a fairly long time this way.
Some say that you should keep your kava powder in the freezer or refrigerator. I don't really agree with this, but if so,
one definitely needs to take extra care to avoid freezer-burn and not to store it next to strong smelling items because
kava takes on other smells and flavors extremely easily.
Once the kava drink is made, it can be stored in your refrigerator for two weeks or more. After which it will "sour"
instead of spoil due to its high starch content. The more sterile your hands and kava making equipment are, the longer
your kava drink will last in the fridge.
"
This is after straining, I'm sore it 'spoils' faster if you are soaking roots