Yes, beef protein powder can be mixed with milk. In fact, it can be mixed with any liquid of your choice, such as water, milk, or juice, to create a protein shake. Beef protein powder is made from hydrolyzed collagen from grass-fed cattle and it is a relatively new type of protein powder. Beef protein powder may have a distinct taste that may be off-putting for some people. Mixing the powder with milk, fruit, or other ingredients can help to mask the taste.