First thing first! There are a few factors to look at when it comes to matcha grades:
SOLUBLE: If your matcha tea is able to dissolve in the liquid, then the tea leaf stalks and veins are separated and you absorb the best quality tea. Matcha tea should dissolve not only in hot water, but also in cold, and dissolve in 15-20 seconds without lumps. If these conditions are met, then you can be sure that your body absorbs only the best part of the leaves of the matcha tea plant. Lower quality matcha tea should tends to be more clumpy.
FLAVOUR: Loose tea leaves may have a bitter taste. This flavour is common in most matcha products. The best quality matcha tea will be rich, umami, soft, sweet and without bitter taste. You shouldn't feel the need for additives. The highest grade is harvested from freshly grown Tencha tea leaves, which are naturally sweet and have a delicate fruity taste.
What if I can't taste it or look at the colour before making the purchase?
Then check the grade, the organic certification and the price. Here's how:
If you are not able to taste or look at the colour personally before making a purchase it would be best to choose a matcha that is classed as 'Ceremonial grade' or 'Premium first harvest', making sure that the matcha powder does not contain preservatives or colorants. Lower grades are usually called Traditional, Daily, Culinary or Cooking. They are much cheaper but also less soluble, of a lifeless green. A great way to use these grades is to use it in bakery recipes, even if the "Premium" grade will always have a better taste.
Also the price is a good indicator of the quality! 30 g of ceremonial grade matcha powder can take over one hour only in the grinding process.