Yeast Nutrients are compounds and elements that are essential to vigorous yeast health and viability. Brewers must ensure optimum yeast health to avoid slow or stuck fermentations, off-flavors, and other problems with beer. The key yeast nutrients are carbohydrates, amino acids, vitamins, and minerals. Malted barley naturally contains a balanced set of these, but high-gravity worts, especially those containing high levels of adjuncts in the form of refined sugars, may not be properly balanced, and yeast performance in these environments may be sluggish. Yeast cultures that have been repitched many times may be particularly prone to inefficient uptakes of nutrients, especially in demanding environments. Many fermentations can be aided by the addition of yeast nutrient preparations, even in all-malt worts. Simple carbohydrates such as glucose, fructose, sucrose, and maltose and often maltotriose are easily metabolized by brewer’s yeast. Yeast cannot, however, assimilate higher polysaccharides (namely dextrins). Therefore, these stay in the finished beer. Amino acids, also referred as free amino nitrogen (FAN), are the yeast’s main nitrogen source, whereas yeast cannot metabolize peptides and proteins. FAN is incorporated into new yeast proteins but the FAN levels influence the yeast’s fermentation performance. Especially for beers with high levels of alcohol, judicious additions of a nitrogen source may be indicated. Vitamins such as biotin, panthotenic acid, thiamine, and inositol are essential for enzyme function and yeast growth. Minerals including phosphate, potassium, calcium, magnesium, and especially zinc are crucial to yeast health and thus successful fermentations. Zinc can be deficient even in all-malt worts, because most of it tends to be lost during lautering. Extra zinc can be added in mineral form (ZnSO4 or ZnCl2), or it can be incorporated in inactive yeast for a more complete nutritional product. German brewers technically adhering to the Reinheitsgebot, which does not allow the addition of mineral salts, have found many ingenious ways to ensure that their yeast gets the zinc it needs. These range from zinc fittings inside the kettle or lauter tun, zinc chains attached to the paddles in the mash mixer, or the old brewer’s trick of adding some live yeast to the kettle. Sometimes a block of zinc is simply hidden at the brewery; shavings will occasionally be taken from it. Weissbier fermentations are particularly susceptible to zinc deficiencies because wheat is rich in manganese, which can block zinc uptake by yeast cells. Finally, yeast needs oxygen to synthesize sterols and unsaturated fatty acids in the yeast cell membrane. This, in turn, allows for ample cell divisions during the yeast’s aerobic phase. Yeast nutrients, judiciously applied, can speed fermentations and promote better attenuation, better flocculation, better yeast storage capability, and better overall beer flavor. As such they have become a standard part of the brewer’s husbandry of yeast.