A bitter taste comes from over extracting the coffee beans. Fixing the problem can come from a few different places. The first is the ground of the beans. A bitter taste may mean they’re too fine for the particular type of bean you’re using. The other place to make an adjustment is the water temperature. If the water is too hot, it could over-extract the grounds. You can also reduce the steep time to change how much flavor gets extracted. A sour taste comes from the opposite problem: under-extracting the grounds. You may need a finer grind to access more of the beans’ natural oils and flavors, or you may need to use hotter water to extract more flavor from the beans. Finally, you can try extending the steep time to give the water more time to release the flavor.