Alexander Gertsman (1); (1) Flottweg Separation Technology, Independence, KY, U.S.A.
Yeast, Fermentation, and Microbiology
Management of surplus yeast is one of the most challenging and important tasks in medium to large size breweries. While some breweries are working on simple concentration of the spent yeast stream to meet the demand of facilities that buy it, some are also recovering beer that can be put back into the process. Buyers of brewers’ surplus yeast are food producers (soup preparation, makers of vegemite), animal nutrition producers, and farmers. Typical target concentration of the product is 20% wt/wt, as this is the maximum value for which it remains in liquid form. If the spent yeast is relatively fresh, beer recovered from it by mechanical separation is typically transferred to green beer process. Special measures of precaution must be taken to enable successful beer recovery, such as minimizing dissolved oxygen pick-up, storage and sanitation. Those who just want to process spent yeast as waste still need to consider concentration of the stream in order not to overload the wastewater system in the brewery. Mechanical separation has been a method of choice for surplus yeast concentration, comprising three methods: centrifugation, membrane filtration, pressure leaf filters and rotary vacuum drum filtration. The last two are less commonly found for new project consideration due to their inefficiency and desire to get away from diatomaceous earth usage. Membrane filtration methods consist of cross-flow technology and less common vibrating membrane filters. The cross-flow systems more commonly contain ceramic membranes, but sometimes polymeric types can also be encountered. While the membrane systems offer the best results when it comes to beer clarity, essentially 0% vol/vol solids, their shortcomings include high energy costs, high operating and maintenance costs, high consumption of water and cleaning solutions for CIP and substantial cooling requirements. Centrifugation can be done with an automatic discharge disc separator, disc nozzle separator and Sedicanter (Flottweg Separation Technology). Centrifuging with an automatic disc separator can only be effective if the inlet concentration is quite low due to limitation in a sludge space and discontinuous type of solids ejection. Very frequent solids ejections lead to quick wear of the machine. Oversizing the machine for strictly sludge pace is a costly solution and also subject of potential dissolved oxygen pick-up, which is an issue of consideration when beer recovery is desired. A nozzle disc separator offers continuous concentrated yeast discharge and is a better solution compared to automatic type but has deficiencies in terms of wetter solids production and also being prone to clogging, since nozzle diameter is quite small, sometimes less than a millimeter. The Sedicanter has the ability to deliver the greatest solids dryness, up to 28% wt/wt of dry matter, while maintaining the same recovered beer quality as other centrifuges. High dry matter directly results in a higher yield of beer.
Alexander Gertsman received a B.S. degree in chemical engineering from New Mexico State University. He has been working with mechanical separation equipment for 20 years, including employment with Alfa Laval and currently Flottweg. Alexander is the brewery industry sales manager for Flottweg Separation Technology and has been responsible for brewery applications and sales in North America since 2005. He is also a profound crafter of homemade kvass, a Russian national malt beverage.