What a good listing tells you, and what a vague one is hiding
Six things separate a listing you can judge from one you cannot. ORIGIN, to a district rather than a country. Uji, Nishio, Yame, Kagoshima, Shizuoka. "Product of Japan" is a customs statement. HARVEST, first flush or later. A seller with first-flush leaf says so, because it costs more. CULTIVAR, where there is one — Samidori, Okumidori, Asahi, Yabukita. Not essential and a strong signal of a seller who knows their supply. MILLING, stone or otherwise. Stone-milled is stated when true. A DATE. Mill date or packing date. This is the single most useful line and the most commonly absent. AN INTENDED USE. Whether the producer made it for usucha, for koicha, or for blending into milk and sugar. That is a genuinely informative statement and it is what "ceremonial" and "culinary" are gesturing at without saying. A listing that gives none of these and instead gives a grade word, a superlative and a story is selling on packaging. That does not make it bad matcha; it makes it matcha you cannot assess before buying.
Judging it once it is open
COLOUR is the fastest signal and it is comparative — you need something to hold it against. Good matcha is a saturated jade or spring green. Olive, khaki and yellow-green mean either later-harvest leaf, stem left in, heat from fast milling, or age. Those four causes look similar and the tin will not tell you which it is. TEXTURE. Rub a pinch between finger and thumb. It should feel like fine talc with no grit at all. Anything gritty was milled coarsely or fast. SMELL, dry. Sweet, green, faintly marine. Flat or hay-like means age; a toasted note means heat somewhere it should not have been. CLUMPING is not a fault. Fine powder clumps because it is fine, and every matcha needs sifting. Clumping is a property, not a defect. IN THE BOWL, a good matcha suspends readily, foams to a fine even head and tastes sweet before it tastes bitter. Bitterness arriving first, with nothing behind it, is the commonest sign of leaf that was never meant to be drunk on its own.
Buying for the thing you will actually make
This is the decision that matters most and it is the one grade words obscure. If you are whisking usucha with water, buy for taste, buy small, and buy recent. A 20 or 30 gram tin finished within a month or two is better practice than 100 grams at a better unit price that spends three months open. If you are making koicha, buy a matcha the producer says is for koicha. Thick preparation uses roughly three to four times the powder in less water and it magnifies everything, which is why koicha grades are separate and expensive. If you are making lattes, a mid-grade matcha with body is often better than a delicate first flush. Milk and sugar cover the fine sweetness you paid for and mute aroma, so the qualities that justify a top-grade price are mostly lost. This is the one place where buying down is the informed choice rather than the compromise. If you are baking, use something made for it. Heat and sugar destroy what is fragile, and colour is usually the point.
Storage decides more than the last twenty pounds of the price
Unopened, keep it cold and sealed. Opened, keep it airtight, dark, cool and dry, and finish it. The refrigerator is genuinely useful for unopened tins and is a trap for opened ones, because taking a cold tin into a warm kitchen condenses moisture onto the powder. If you refrigerate an opened tin, let it come to room temperature fully before opening it. If that sounds like a nuisance, the simpler answer is to buy smaller tins more often, which is what most people who drink it regularly end up doing.