High-Gravity Brewing and Distilling—Past Experiences and Future Prospects

High-gravity brewing employs wort (15–20°P original gravity) at a higher than normal concentration, and to obtain sales-gravity beer, dilution with water (usually carbon filtered and deoxygenated) is required at a later stage in processing. Using this method, increased production demands can be met without significant expansion of brewing, fermenting, and storage facilities. Scotch whisky production, particularly grain whisky, also is increasingly employing high-gravity techniques (18–21°P wort) during a continuous fermentation procedure. The principal advantage to this procedure is the more efficient use of existing processes. The disadvantages of high-gravity brewing include decreased beer foam stability, a variety of stress effects on yeast, and problems with beer flavor matching compared with sales-gravity brewed beers. The stress effects of high-gravity wort also include enlargement of the yeast vacuole and changes in the topography of the yeast cell surface. Hydrodynamic stress effects on yeast are also a problem, particularly when employing centrifugation at the end of fermentation to crop yeast for recycling into a subsequent fermentation. Finally, difficulties encountered in both brewing and distilling include the inability of yeast to completely utilize the largest fermentable wort sugar—maltotriose. This is particularly the case during grain whisky production by continuous fermentation under high-gravity wort conditions.