Anything that's been open for more than six months should go. Matcha doesn't spoil dangerously, but it loses its sweet, grassy flavor and picks up a bitter, stale taste. If it smells musty or flat, retire it.

Tools that are broken or impossible to clean are also on the chopping block. A whisk with bent tines won't produce the smooth froth you want. A sifter with rust? Toss it.