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.