Changes in cell volume occur when yeast is propagated in worts of increasing original gravity (OG) in the range 7 5 to 17 5°P Using image analysis to measure cell volume, the mean individual cell volume of ale and lager yeast increased by up to 30% as OG increased to 17 5°P. Propagation of yeast in high-gravity wort (17 5°P) has a deleterious effect on yeast quality during subsequent high-gravity fermentations. The mean cell volume of yeast changes during storage and this has been identified as a contributing factor to over-pitching of fermentations. A reduction in mean cell volume of up to 19% for ale yeast and up to 7% for lager yeast has been observed. Using image analysis, a new pitching regime was developed which improves fermentation consistency. A rapid technique has been developed to determine the glycogen content of yeast on an individual cell basis using a combination of image analysis technology and staining of yeast cells with an I2 KI solution. Analysis of the distribution of yeast glycogen during fermentation indicates that a fraction of yeast cells do not dissimilate glycogen. Therefore, conventional glycogen analysis of yeast used to inoculate fermentations is of limited use, unless information regarding the proportion of cells which utilise glycogen is known. Thermal gradients in yeast crops of 3 5°C were recorded within 5 hours of unmixed storage, using a specially designed cooling rig. These gradients increased with increasing yeast metabolic activity to a maximum of 11°C. Using a custom-built yeast storage vessel, it was determined that mechanical agitation achieves better mixing than recirculation of slurry through an external loop. In all trials, a dense biomass layer (up to 75% w/w) developed on the slurry surface (due to CO2 evolution), in which the yeast viability was up to 13% lower than in the remainder of the vessel.