Matcha powder can be used in many recipes, including baking.  However, it can change to a brown color when exposed to high heat for too long or when used in baked goods containing high amounts of sugar. Two main reasons why matcha cookies may turn brown is due to prolonged baking times and using larger amounts of sugar.  Making low-carb cookies using a sugar-free sweetener keeps them a beautiful, bright green. Stored matcha can naturally turn brown when exposed to heat and air, so it’s best to keep it in an air tight, sealed container and store in a cool, dark place. Some matcha products add ingredients to help the powder retain its green color, even when baked for longer periods.  Make sure to check the ingredient list for additives and consider purchasing a 100% organic product.