Instruct: Classify a given Amazon review as either positive or negative.
Query: Spiru-Tein Products/Powders

The one BIG problem I have with Spiru-Tein powders is that even though the packaging states they mix easily or instantly dissolve, or something to that effect, nothing could be further from the truth. After stirring, stirring, stirring, some of the power remains on top of whatever liquid (e.g. milk) you have mixed (or tried to mix) it with. I have even used an electric mixer to try and get it thoroughly blended and it still remains undissolved.