Shelf Life: Sealed Versus Opened

The date printed on the package applies to the unopened product. Opening starts a different clock.

Sealed: six months to a year

Matcha products commonly carry best-before dates in that range.

Sweetened versions are sometimes given longer. Sugar binds free water, reducing what microorganisms can use — the same principle that preserves candied fruit.

Opened: two weeks to a month

Sellers of matcha typically suggest this window.

A date six months out does not change it. From the moment air reaches the powder, color and aroma start shifting.

Why the gap is so wide

Matcha is finely milled leaf. Particles run around 10 microns, and finer grades reach 1 to 5 — roughly an order of magnitude below wheat flour at 30 to 60 microns.

More surface area means faster oxidation and faster loss of volatile aroma. Whole-leaf sencha holds up considerably longer.

Past the date

Best-before indicates quality, not safety. Nothing changes on that specific day.

But color dulls, aroma thins, and flavor flattens. Stop if you notice an off smell, clumping from moisture, or anything resembling mold.

Which determines what size to buy

Larger packages cost less per gram and mean nothing if you cannot finish them.

At 20 g per serving, 300 g is 15 cups — about two weeks daily, roughly two months twice a week.

Choose a size that fits inside the post-opening window and the per-cup arithmetic holds.

Track the opening date

Write it on the package with a piece of tape.

The printed date tells you nothing about how long it has been open, and that is the number that matters.