The four usual causes
- Leaf quality — late harvests and sun-grown leaf carry more catechins, the main bitter compounds.
- Water too hot — boiling water scalds matcha; bitterness rushes forward.
- Too much powder — concentration amplifies everything, harshness included.
- Age and air — oxidized matcha loses sweetness first, leaving bitterness exposed.
Shade changes the chemistry
Weeks of shading before harvest raise L-theanine (umami and sweetness) and lower catechins. That is why ceremonial-grade matcha, made from well-shaded first-flush leaves, tastes rounder than budget powder at the same strength.
Bitterness is information: about the leaf, the water, or the tin.
How to fix a bitter bowl
Let boiled water cool to around eighty degrees Celsius before whisking. Sift the powder, start with two grams per seventy milliliters, and adjust gradually.
Store your tin sealed, cool, and dark, and finish it within a month or two of opening. If bitterness persists after all of this, the leaf itself is the limit — consider stepping up in grade.
A brisk edge is character; a harsh edge is a fixable fault.