Monitoring a fermentation allows the producer to ensure the fermentation is performing as required and allows prompt remedial action if any problems develop. The normal methods used are measurement of sugar (or, more accurately, dissolved solids) by hydrometry, measurement of temperature and sensory evaluation. One mole (180 g) of glucose yields about 103 kJ (24.5 kcal) as heat, and each percent of sugar (1◦ Brix) in the must generates enough heat during fermentation to raise its temperature by 1.3 ◦C/l, if no heat is lost. Hence, a wine must of 22 ◦ Brix would generate enough heat to raise its temperature by nearly 30 ◦C during the fermentation process, although some of this heat will be lost with the evolved CO2 (Jackson, 2000b). Important ‘fermentation problem indicators’ are high or low fermentation rate, temperature variations, turbulence and production of off odors such as H2S. In difficult fermentations one of the first signs of a problem is the yeast settling as the fermentation slows down. It is thought that yeast cells die very quickly at the bottom of the tank due to sugar and nutrient depletion in that area, and that yeast that are in suspension are more likely to survive. Certainly, brewers know that suspended yeast cells provide the most efficient fermentation of beer wort (Section 2.6.4). Measures to rescue such ‘sluggish’ or ‘stuck’ fermentations include the increase of fermentation temperature, addition of vitamin supplements, limited aeration by pumping over and reinoculation (Pretorius, 2000).