Typically, you would make proffee using ice cubes because it is easier to mix protein powder with cold coffee. A refreshing cold beverage is also preferable for those looking for a post-workout protein hit. However, if you'd rather make a hot proffee using hot water and hot coffee, you can. This might be slightly more difficult to achieve, though, as depending on the type of protein powder you use, it may become clumpy or lead to a foamy drink in hot water.