While ingredient errors on the part of mix-blending can occur, they are extremely rare. Usually the problems experienced at shop level are the results of preparation errors or machiney being out of spec. Following is a list of the most common problems in each of the two errors. Assumming a full scoops weighs a certain amount is very risky. For volume wholesalers running batches from full bags, assumming that a 50 or 100 pound bag does , in fact, weigh 50 or 100 pounds, can also be risky.
Chemical reactions occur faster with the addition of heat, slower without it.
Too much or too little batter temperature throws this entire sequence off. Too high a temperature will reduce your volume. Either will result in poor shape. This has a huge effect on how a donut reacts, primarily because the more acidic the grease is, the more the leavening in the donut is going to react to it. Filtering the fat on a regular basis screens out particles which cause your shortening to break down more rapidly, but in time the ph will drop anyway.