There are a few things you can do to help remove some of the bitterness from Brussels sprouts such as adding lemon juice or apple cider vinegar, red pepper flakes, sugar, and olive oil. Elements of heat, fat, acid, and sweetness are simple ways of changing the flavor to one that's less bitter. Another simple step is to remove the outer leaves. These leaves tend to be more bitter and they also tend to fall off on their own as you slice them.