Kneading in a mixer is fast and does not tire your hands; kneading by hand lets you feel directly how the dough is developing. The two methods build the same gluten network, but carry two distinct risks: a mixer can overknead and heat the dough, while hand kneading can leave it underkneaded. Choose the method based on the dough's hydration and batch size: stiff dough and large batches suit a mixer, while small, wet batches are better kneaded by hand. In either method, the dough itself is the measure.
The most visible difference is the time. A bread dough that takes 10–15 minutes to knead by hand reaches the same point in 5–8 minutes at medium speed in a mixer. This is because a mixer does much more mechanical work per unit of time. That is an advantage, but also a risk: it is nearly impossible to overknead by hand because your arm gets tired and you stop; a mixer does not tire and can easily overwork the dough if left unattended. Hand kneading has a less visible benefit too: you can feel the dough’s condition at every moment with your fingers, and make decisions by touch rather than by measurement.
The second difference is heat. The mixer’s dough hook keeps turning the dough, creating friction and raising its temperature; during long mixing, this increase can reach several °C. This matters because the target dough temperature is 24–27°C / 75–80°F: when mixing in a warm kitchen, use colder water and, if needed, replace some of the water with ice. Dough kneaded by hand heats up much more slowly, so this is usually not taken into account. If you measure and record the dough temperature with a thermometer, a few trials will show how much the mixer raises the temperature in a given number of minutes.
Overkneaded dough shows clear signs: it first becomes very smooth and shiny, then slackens, gets sticky, and becomes difficult to handle. At this point, the gluten network has been damaged and the condition is irreversible. This almost always happens with a mixer. Prevention is simple: run the mixer at low or medium speed, divide the mixing time into short intervals, and check the dough between intervals. High speed is never necessary for bread dough. When kneading by hand, continually dusting the counter with flour can cause a similar problem because it unknowingly changes the dough proportions.
Choose the method based on the dough. Low-hydration, stiff dough is hard to knead by hand and suits a mixer; the same is true for batches containing more than 1 kg of flour. In contrast, a mixer may wind very wet dough around the hook and fail to work it properly; the stretch-and-fold method gives better results for that dough. With small batches, a mixer may not reach the bottom of the bowl, leaving some of the dough untouched; in that case, hand kneading is both faster and cleaner.
Whichever method you choose, use the same test and judge the dough itself. Pinch off a small piece and slowly stretch it between both hands; if it stretches into a thin membrane without tearing, the gluten has developed. Apply this test in the same way for each of the 2 methods, and let it take priority over the clock. When using a mixer, stop the machine and touch the dough by hand; judging by looking into the bowl can be misleading, and this is often how overkneading begins.