You can indeed make cold brew and then heat it up. It won't suddenly turn bitter and lose its sweeter flavor. That's because the acidic compounds reside in the coffee grounds, so once they're removed (and please don't forget to remove those grounds before heating!), you can then prepare your coffee any way you like. So go heat it up on the stove or in the microwave (just make sure to keep it below a simmer!) and then add whatever else you normally would to your hot coffee. But our bet is you'll find yourself needing less sweetener than you did before. For a quick tutorial on heating your cold brew on the stove, check out these instructions.