There are a few reasons why your granola may taste bitter: Over-toasting: If the granola is toasted for too long or at too high of a temperature, it can become bitter. Burnt nuts or seeds: This can happen if you add more nuts than oats. Rancid ingredients: If the nuts, seeds, or oils used in the granola are rancid, they can also contribute to a bitter taste. To prevent bitter tasting granola, make sure to follow the recipe carefully, check the granola frequently while toasting, and use fresh, high-quality ingredients.