Gritty premium culinary matcha usually comes from not sifting, using water that's too hot (which clumps the powder), or not whisking enough. Start by sifting your matcha into the bowl, use water around 175°F (80°C), and whisk in a W motion for at least 30 seconds until frothy. If it's still gritty, check your whisk—a fine bamboo chasen works better than a regular fork.