A strip of flour or butter left unmixed at the bottom of the bowl is usually a matter of adjustment, not machine power. On stand mixers, the height of the head relative to the bowl is adjusted with a single screw, and the factory setting can easily shift during transport. The correct setting is found with a flour test: the whisk should sweep the flour without rubbing against the bottom.
The most common complaint about stand mixers is an unmixed strip at the bottom of the bowl. In cake batter, this strip appears as a clump of flour and butter; in cream, as unwhipped liquid. Users often blame the machine and think it lacks power. But the cause is almost always a shifted head height. On stand mixers, the whisk is adjusted to sit a certain distance from the bottom of the bowl, and this distance can be changed with a screw. The factory setting can easily shift during transport and extended use.
You can tell whether the adjustment is correct with a simple observation. Put the bowl in place, sprinkle one 4 ml measure of flour into it, attach the whisk, and lower the head. Do not turn the machine on; slowly rotate the whisk by hand. With the correct adjustment, the edge of the whisk sweeps the flour on the bottom away, leaving a clean trail without rubbing against the metal. If an untouched ring of flour remains on the bottom, the whisk is too high. If the whisk rubs the bottom, makes a scraping sound, or catches when turned by hand, it is too low, and this second condition causes more damage.
On most models, the adjustment screw is near the hinge where the head connects to the body; on some, it is underneath and visible when the head is raised. The direction varies by model, so check the appliance’s own manual to find which way lowers the whisk. Turn the screw in very small increments and repeat the flour test after each adjustment; turning it several times at once can move the setting to the opposite extreme. Use the measurement with the head lowered, because its position changes slightly when the head is lowered.
A whisk that rubs the bottom causes two kinds of damage. First, it damages the bowl: a metal whisk scratches the bottom of a stainless-steel bowl, and those scratches leave gray marks over time; on coated bowls, it removes the coating. Second, it damages the whisk itself: the wire tips wear down from constant friction, the shape of the wires changes, and the whisk no longer mixes evenly. Friction also increases the load on the motor. That is why the whisk should not touch the bowl; it should sit close enough to sweep the bottom.
If the problem continues even when the adjustment is correct, there are a few other possible causes. You may be using the wrong attachment: the wire whisk is for light mixtures, the flat beater for cake batter, and the dough hook for bread dough. If there is too little in the bowl, the whisk may not reach it at all; smaller amounts require a smaller bowl. Third, whatever setting you use, ingredients collecting on the sides need to be scraped down with a spatula from time to time; this is not a malfunction but normal use of any mixer.