Instruct: Classify a given review into positive or negative sentiment.
Query: Clumpy. Doesn't mix.

This is the worst protein powder I've ever purchased -- no matter what I try, I end up with a glass full of clumpy powder. I just can't get this stuff to mix well with any reasonable amount of water or milk. I think I'll go back to using Optimum, even though Optimum now costs $20 more for 5 lbs.