Thinking about establishing our own set of criteria for different grades. Comments appreciated!!!
CEREMONIAL: Definitely anything considered by Japanese tea ceremony practitioners in Japan as koicha, but that doesn't say very much for those who don't know. This level should be bright green, have a "rich" aroma and flavor. It can be bitter or creamy, but should have strong umami flavors creating the richness. The grains should be small enough that you don't taste any grainy texture whatsoever. Spring harvest. An elite connoisseur will say that it must be handpicked and milled by stone, but we'll reserve that for a top level sub-class "Imperial Class", a very excellent example maybe labeled "Master Class".
LATTE: There is no "latte grade" in Japan, but rather matcha meant for thin tea or usucha used in most tea ceremony schools is generally considered to be lower in quality and therefore cheaper. The above should hold true but a lower level of richness coming from either a longer growth period, less shading, a less suitable cultivar (Yabukita etc), or simply the age of the powder (degradation of color, flavor and aroma).
The reason for the high standard is that we expect and desire that consumers sometimes drink their matcha straight.
Spring harvest and most likely ball-milled (the process has more heat generated by friction degrading the powder a bit).
CULINARY: At this level, you can still drink the matcha straight without making too much a sour face...unless you are a true connoisseur at which point you'd probably go wash out your mouth. Bitter without much umami richness and more significantly a definite grainy texture in your mouth.
All of these bad points can be negated by flavoring (as in lattes) or use of the matcha as flavoring in baked goods, etc.
Likely spring/summer harvest blend or a summer harvest. Color will be dull, yellowish green.
INDUSTRIAL: Very bitter, very grainy to taste resulting primarily from the use of large bancha level leaves to make the tencha (harvested in late summer or autumn). This matcha level is not meant for drinking at all due to its graininess but with the right flavoring it might be suitable for lattes.
Very dull yellow-green. Very little aroma. Matcha taste but very grainy.