Matcha, and why a powder is a different problem
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Surface area is the whole story
Grinding leaf to a fine powder exposes an enormous amount of surface to air, so oxidation and loss of color and aroma happen in weeks rather than months. It is the same mechanism that makes ground coffee stale faster than whole bean, taken further.
Color is the quality signal buyers use
A bright green that dulls toward olive is the visible form of the decline, and it is the first thing a customer judges. That makes light protection and a tight seal commercial necessities rather than refinements.
Small containers, not large ones
A large container of matcha is a container whose contents spend months over a growing air space. Small formats sold more often is the right answer even though it looks like the more expensive way to package, and buyers who know the product expect it.
It does not off-gas, so sealing is simple
Unlike coffee there is no contradiction to resolve: a tight, opaque, well-filled container is straightforwardly correct. The only reason not to seal it completely is that there is no reason not to.
Grade words mean little
Ceremonial and culinary are trade terms without legal definitions, and they are used inconsistently. Describing what the product is and where it came from carries more weight than reaching for a grade word whose meaning you do not control.
It belongs on a different shelf
Our bulk shelf for this property runs from about 950 ml upward, which is storage and refill scale. A retail matcha wants a small opaque container with a tight closure, and that is the powders shelf rather than this one.
Store it cold, and open it warm
Refrigerated storage slows the decline meaningfully, and taking a cold container into a warm room and opening it condenses water onto the powder. Let it reach room temperature sealed before opening, every time, which is the same rule the freezing paragraph gives for coffee.