A fermenting system is disclosed comprising a fermenting vessel and an ultrasonic mixer for mixing nitrogen or enzymes into the fermenting liquid, the apparatus being arranged such that the fermenting liquid is directed from the fermentor using a pump, with subsequent addition of enzymes and/or nitrogen to the liquid, and wherein the fermenting liquid then passes through the ultrasonic mixer and back into the bottom of the fermentor, thereby lifting and mixing the liquid in the fermenting vessel. The ultrasonic mixer distributes the enzymes and nitrogen in the liquid, and creates smaller nitrogen bubbles which aid lifting and mixing of the liquid in the fermentor. The apparatus and method can be used for fermenting thick mixtures of waste bread and confectionary which may sediment on the bottom of the fermenting vessel, leading to an increased alcohol yield in such fermentations. The enzymes used may include alpha-amylase.
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