Tentative Schedule

Yeast Flocculation, Vitality, and Viability
April 20-21, 2009, Hyatt Harborside, Boston, MA

Monday, April 20, 2009

7:30 – 8:15 Morning Brew (optional)
Yeast flocculation terms & basics
Greg Doss, Wyeast Laboratories, Odell, OR U.S.A.

Session I

8:30 – 9:00 Opening remarks

9:00 – 9:45 History and overview of flocculation
Alex Speers, Dalhousie University, Halifax, NS Canada

9:45 – 10:30 Flocculation assays
Anne Huuskonen, VTT, Espoo, Finland
Alex Speers, Dalhousie University, Halifax, NS Canada

10:30 - 11:00 Break

11:00 – 11:45 The genes behind yeast flocculation: A brewer’s perspective
Sebastiaan Van Mulders, K.U. Leuven, Heverlee, Belgium

11:45 – 12:30 Flocculation genetics FLO11
Anne Dranginis, St. John's University, New York, NY U.S.A.

12:30 – 14:00 Lunch

Session II

14:00 – 14:45 Investigations on malt causing premature yeast flocculation
Joseph Lake, Dalhousie University, Halifax, NS Canada

14:45 – 15:30 Factors that promote the premature yeast flocculation condition in malt
Samantha Walker, Brewing Research International, Surrey, United Kingdom

15:30 – 16:00 Break

Session III

16:00 – 16:45 Yeast vitality and stress responses—Novel investigative approaches
Graeme Walker, University of Abertay, Dundee United Kingdom

16:45 – 17:30 Stress viability and dried yeast
Chris Powell, Lallemand Inc., Montreal, QC Canada

Tuesday, April 21, 2009

7:15 – 8:00 Morning Brew (optional)
Vitality/viability terms
Chris White, White Labs, San Diego, CA U.S.A.

Session IV

8:00 – 8:45 Vitality/viability assays
Frithjof Thiele, TU Munchen – Freising, Weihenstephan Germany

8:45 – 9:30 Effects of serial repitching
Katherine Smart, University of Nottingham – Loughborough United Kingdom

9:30 – 10:10 Vitality/viability - A brewers perspective
William Maca, MillerCoors, Milwaukee, WI U.S.A.
Presentations will be handed out onsite.

10:10 – 10:30 Break

Session V

10:30– 11:15 Yeast vitality – A process approach
Peter Bouckaert, New Belgium Brewing, Fort Collins, CO U.S.A.

11:15 – 12:00 Interactive panel discussion
Moderator: Lyn Kruger, Siebel Institute & World Brewing Academy, Chicago, IL U.S.A.

Abstracts and Biographies

Yeast flocculation terms and basics
G. Doss, Wyeast Laboratories Inc., Hood River, OR
This presentation will be a general introduction to yeast flocculation. Topics to be discussed include flocculation terms and definitions, different flocculation models and mechanics, and how factors in the brewhouse influence flocculation.

Greg Doss earned a B.S. degree in microbiology from Oregon State University in 1996. Following college, he brewed professionally for five years in Hood River, OR, and Seattle, WA. In 2000, Doss joined the staff at Wyeast Laboratories as a microbiologist and has managed the QC/QA Department since 2005.

Back to top

History and overview of flocculation
A. Speers, Dalhousie University, Halifax, NS, Canada
Brewing yeast flocculation has and continues to be a concern to brewers and brewing scientists. The flocculation characteristics of yeast strains are important to beer fermentation and clarification. While cell flocculation has been examined for over a century and has been the subject of a number of reviews, our view of the process is unclear. This presentation will outline past investigations, with particular reference to investigations from Pasteur to this decade. In essence, flocculation is driven by the makeup of the yeast cell wall, as well as the physical behavior and chemical makeup of the fermenting medium. Forces that influence cell-to-cell binding include zymolectin and hydrophobic and electrostatic interactions. These factors will be discussed, and gaps in our knowledge highlighted. Minimal reference will be made to flocculation measurement, genetics, and premature yeast flocculation, as other speakers will examine these topics in detail.

Alex Speers is a professor in the Food Science and Technology program at Dalhousie University, Halifax. Speers received his graduate education in food science at the University of British Columbia, Vancouver. At Dalhousie University, he instructs students in brewing science, quality assurance and food product development. In the past, Speers has been employed in the Quality Assurance departments of both Labatt and Molson Breweries. His current research interests include various aspects of the brewing process, including fermentability, yeast flocculation, premature yeast flocculation, extract calculations, and the properties of (and problems created by) b-glucan and arabinoxylan polymers. He has organized and/or presented brewing workshops in China (Changzhou, Qingdao, and Yangzhou) from 1997 to 2005 and recently at brewing conferences in Honolulu, Nashville, and San Francisco. Speers has spent sabbaticals at CUB/Fosters in Melbourne, Australia, and the Columbia Brewing Company in Creston, BC. On occasion he instructs at the Siebel Institute of Technology. Speers belongs to several professional societies and is a member of the editorial boards of Food Research International, the ASBC Journal, and the Journal of the Institute of Brewing. He also currently chairs the Editorial Board of the Master Brewers Association of the Americas. He has published or presented more than 100 papers.

Back to top

Flocculation assays
A. Huuskonen, VTT Technical Research Centre of Finland, Espoo, Finland; A. Speers, Dalhousie University, Halifax, NS, Canada; J. Rautio, PlexPress Oy, Helsinki, Finland; and J. Londesborough, VTT Technical Research Centre of Finland, Espoo, Finland
While yeast flocculation is a continuing source of research, no international method has been accepted to monitor the progress of cell flocculation. This presentation will report on previous, existing, and potential methods for yeast flocculation assay. We will review the Helm and Burns methods and derivatives, adherence and kinetic methods, and absorbance techniques. Standard methods will also be reviewed. In addition, measures of cell wall hydrophobicity and zymolectin ‘density’ will be discussed. Finally, research with the TRAC method of monitoring flocculation gene expression will be presented.

Anne Huuskonen is a research scientist at VTT Technical Research Center of Finland. She studied biochemistry, plant physiology and molecular biology at the University of Helsinki and carried out research for her M.S. degree at VTT. She also worked for Genencor International Inc. on EC-funded projects concerning filamentous fungi. She has participated in several yeast-related projects at VTT, especially those dealing with the physiology of brewer’s yeast under very high gravity conditions. Currently she is studying protein production in filamentous fungi.

Back to top

The genes behind yeast flocculation: A brewer’s perspective
S. Van Mulders, K. Verstrepen, and F. Delvaux, Katholieke Universiteit Leuven, Leuven, Belgium
The brewer’s yeast genome encodes a ‘Flo’ (flocculin) adhesin family responsible for flocculation and other related aggregation processes. Adhesins are adhesion glycoproteins decorating the outer surface of the cell wall. They offer yeast cells the potential to interact physically with each other. The tendency of yeast cells to apply their adhesins and aggregate into macroscopic flocs has been an eye-catching phenomenon for brewers for more than 100 years. More importantly, this floc formation, or flocculation, is of considerable importance in brewing and biotechnological industries, because it results in a cost-effective and environmentally friendly technique to separate yeast cells from beer. Due to intrinsic characteristics of the adhesin-encoding genes, such as the presence of highly variable tandem repeats in their central region, and their subtelomeric location, these ‘FLO’ genes possess the remarkable capacity to evolve and diverge many times faster than other genes. Consequently, each brewer’s yeast strain will possess its personal reservoir of ‘FLO’ genes. Even more striking is that, when considering the same strain, this strain-dependent pool of genes can change perpetually. Moreover, epigenetic regulation of the ‘FLO’ genes, which encompasses heritable changes caused by mechanisms other than changes in the underlying DNA sequence, creates an additional source of variation. In actual practice, this genetic and epigenetic variability triggers changes in adhesin structure and expression, which in turn may result in an altered flocculation pattern. This may have important implications for the brewer in maintaining an efficient beer clarification and/or filtration. Top- and bottom-fermenting brewer’s yeasts display a distinct genomic makeup. However, they should flocculate preferentially at a well-defined point in time, when the fermentable sugars are depleted. For both yeast types, the genetic background of yeast flocculation will be discussed. In addition, the consequences of phenotypic variability on the occurrence and timing of yeast flocculation in the beer fermentation process will be reviewed.

Sebastiaan Van Mulders received a M.S. degree in bio-engineering, option industrial microbiology, from the Katholieke Universiteit Leuven (K.U.Leuven) in 2006. For his M.S. thesis, he joined the Centre for Malting and Brewing Science (K.U.Leuven) to study accelerated fermentation systems with immobilized or suspended yeast cells for the production of beer. After graduation, he started work on his Ph.D. degree at the Centre for Malting and Brewing Science, with a grant from the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT-Vlaanderen). Van Mulders investigates the adhesion properties of Saccharomyces cerevisiae for the optimization of fermentation-based biotechnological processes. He is also involved in a Belgian Federal Science Policy Office and European Space Agency PRODEX research program on the cellular adhesion, biofilm formation, and invasive growth of the model eukaryote S. cerevisiae in microgravity. His main research interests concern yeast and fermentation technology from a yeast genetic and epigenetic perspective.

Back to top

Flocculation genetics FLO11
Anne Dranginis, St. John's University, New York, NY
As nonmotile organisms, yeast rely on selective adhesion as an important means of interacting with their environment. This adhesion is mediated by cell wall proteins known as flocculins. One of the most important flocculin genes is FLO11, which has been found in all strains investigated. Yeast use the Flo11 protein to stick to a variety of surfaces, including plastic, agar, and human epithelial cells. More importantly, yeast use Flo11 to adhere to other yeast cells to form a wide variety of structures. Of greatest interest to the brewing and wine industries are the flocs mediated by Flo11 and the flors, specialized biofilms responsible for production of sherry wine. Flo11 is also responsible for the formation of branched filamentous chains of cells called pseudohyphae, as well as for complex microbial mats, biofilms, and colonies with characteristic wrinkled morphologies. Not all yeast strains express every one of these Flo11-dependent phenotypes. Strain Sigma 1278b, for example, requires Flo11 for pseudohyphae formation but does not flocculate. Strain S. cerevisiae var. diastaticus, on the other hand, requires Flo11 for flocculation but does not form pseudohyphae. These strain-specific differences are naturally occurring experiments in the factors that govern Flo11 effects on morphology, and we are exploiting them to investigate mechanisms of adhesion. We have sequenced the FLO11 gene from several yeast strains and have found substantial differences in the DNA sequences, particularly in the central domain of the encoded protein. The effect of these sequence differences is being investigated through “gene swap” experiments, in which the FLO11 gene of one strain is used to replace that of another. We have purified Flo11 protein and used it to coat microscopic beads, thus creating an in vitro adhesion system. Surprisingly, these coated beads bind only to cells that express Flo11, showing that the adhesive target is other Flo11 molecules; this is, therefore, a homotypic reaction. Using this system we have established that the amino terminal domain of the protein is the adhesion domain, and the central domain of tandemly repeated amino acids is the receptor. Flocculation appears to be a protective adaptation and often occurs when cells have exhausted fermentable carbon sources. Cells within the flocs are protected from environmental stressors such as ethanol. These flocs may be limited to cells of a particular strain by the homotypic adhesion of Flo11. Thus, yeast that express Flo11 may cooperate with yeast of the same strain and exclude other strains from the protective flocs. This situation is of interest in terms of the evolution of cooperation and will be explored.

Anne M. Dranginis is a professor of biological sciences at St. John’s University in New York City. She received a B.S. degree in zoology from the University of Massachusetts and a Ph.D. degree in cell and molecular biology from the University of Michigan. As a staff scientist at the National Institutes of Health in Bethesda, MD, from 1984 to 1992, she studied yeast as a model system for eukaryotic gene regulation, and there began studies on flocculation. Since 1992 she has continued these studies at St. John’s University, where she also teaches molecular biology and evolution. Her current research interests include mechanisms of adhesion by Saccharomyces cerevisiae and Aspergillus nidulans, evolution of fungal adhesins, and the structure of fungal cell walls.

Back to top

Investigations on malt causing premature yeast flocculation
J. Lake and A. Speers, Dalhousie University, Halifax, NS, Canada
Premature yeast flocculation (PYF) is an unwanted condition that occurs during the fermentation of wort in which yeast settles out of the medium at an accelerated rate compared with normal fermentations. This leaves the fermented wort under-attenuated, often requiring substantial troubleshooting to render the beer saleable. In extreme cases, the beer cannot be sold. Traditionally, PYF events were considered to be sporadic, but recent arguments suggest that PYF may be a problem that is more common than previously thought. Even though PYF is a worldwide dilemma, its nature and mechanisms are still not completely understood. Building on previous reported results, the present study focuses on two aspects of PYF: methods of detecting PYF and the active components of PYF-inducing factor(s). With regards to methods of detection, a small-volume (15 mL) fermentation assay was developed. It was determined that the addition of 4% glucose (w/v) and fermenting at 21°C compensated for height reductions, yielding adequate average shear rates to keep yeast in suspension in the 15-mL test tube fermentation. This low-volume fermentation improved on tall tube fermentors, detecting PYF worts in 48 h while requiring less wort. A photometric device was constructed to examine yeast in suspension more thoroughly in small-scale fermentors. Uninterrupted measurement of fermentations yielded more than 800 data points that were subsequently modeled using a nonlinear application of two general logistic curves. Although the model proved to be an accurate means of statistically identifying a PYF wort compared with a control, the amount of data required did not allow the nonlinear technique to be applied to normal fermentations. To keep PYF factors as close to their native composition as possible, filtration and small-scale fermentations were utilized to isolate and determine active PYF components. Through a series of membrane filtrations, it was determined that removal of PYF wort components with molecular weights >100 kDa reduced PYF activity. The reintroduction of these 100-kDa components into a normal fermenting wort induced PYF. Several fermentation tests with both the 100-kDa PYF-inducing retentate and a series of pure standards indicated that ferulic acid is most likely directly involved in the activation of PYF.

Joseph Lake recently graduated with a Ph.D. degree in food science from Dalhousie University, Halifax, NS, Canada. His research was conducted under the guidance of Alex Speers and involved examining the phenomenon of premature yeast flocculation. Additionally, Lake has spent four months in industry working with Marcia Browers, Xiang Yin, and Karren Churchill at Prairie Malt Limited studying barley toxins, fermentations, and various malting strategies. Lake is an active member of the American Society of Brewing Chemists, receiving three scholarships (2006–2008), as well as being awarded travel scholarships to present work at the 2007 ASBC meeting in Victoria, BC, and WBC 2008 in Hawaii. Currently Lake is beginning his career in the industrial realm of food science.

Back to top

Factors that promote the premature yeast flocculation condition in malt
S. Walker and G. Fisher, Campden BRI, Nutfield, Surrey, UK
Premature flocculation of yeast can occur during fermentation while fermentable sugars remain high (although this is not always the case), resulting in a dramatic reduction in the number of yeast cells in suspension, which leads to an incomplete fermentation and product quality issues for the brewer. It is widely acknowledged that certain polysaccharide/protein complexes arising from malt husk can promote premature yeast flocculation (PYF) in susceptible yeasts. What is less clear are the malting conditions that promote the formation of these factors. This talk will be split into two parts. In the first half, we will discuss the findings from laboratory trials on the factors in malt processing that contribute to the formation of PYF-positive malts. It is well known that many different methods exist for PYF testing, and individual establishments have tailored these to the requirements of the brewery in which the malt is destined to be used. While these methods work well for predicting the likelihood of malts promoting the PYF condition in their laboratories or breweries, the subtle differences in methods make it difficult for an individual to compare results from different establishments. At the 2008 World Brewing Conference (WBC) in Hawaii, a PYF network was initiated to bring together academics, brewers, and maltsters to share their knowledge of factors that might promote the PYF condition and to work toward a common method. The vision of the network will be discussed in the second half of this talk, as well as the future of PYF and PYF testing.

Samantha Walker holds a degree in agricultural and food sciences from Nottingham University. She was awarded a doctorate from the University of Wales, Cardiff, for her work on the growth of microbial colonies in food and food models. Walker subsequently spent 18 months as a higher scientific officer in the Molecular Genetics Unit at the Veterinary Laboratories Agency, Weybridge. She joined Brewing Research International in 1998 as a senior scientist to develop molecular methods for the detection of beer spoilage organisms. She has worked with other team members on a number of research projects, including lab-on-a-chip methods for barley varietal identification, dispense hygiene, development of processing aids, fermentation, new product development, and the evaluation of antibody-based kits for gluten and ochratoxin analysis. Walker is currently working as a project manager within the Research and Development team and is responsible for the Premature Yeast Flocculation (PYF) network. She is project coordinator for a DEFRA Link project, researching the impact of anaerobic fermentation on the flavor stability and shelf life of beer.

Back to top

Yeast vitality and stress responses—Novel investigative approaches
G. Walker, Abertay University, Dundee, Scotland, UK
An understanding of brewing yeast cell physiological phenomena is a prerequisite for ensuring consistent yeast fermentation performance and product quality. Several factors can deleteriously impact yeast growth and metabolism, notably physicochemical and biological stress factors. To assess the physiological condition of yeast cultures employed in brewing fermentations, we need rapid, robust, and reliable methods. In recent years, several such methods have been developed to monitor yeast viability and vitality, but are they truly assessing reproductive and metabolic capacities, respectively? This presentation will describe some novel approaches to gain deeper insight into brewing yeast vitality and stress responses. For example, flow cytometry, fluorescence microscopy, transcriptomics, atomic force microscopy, and membrane fluidity probes have been employed to assess various yeast physiological phenomena. Recent research findings using such techniques with brewing strains of Saccharomyces cerevisiae will be presented and discussed.

Graeme Walker graduated with a B.S. degree in brewing and biochemistry in 1975 and completed his Ph.D. degree in yeast physiology in 1978 (both from Heriot Watt University, Edinburgh). He was conferred a D.S. degree by Abertay University in 2004. Walker’s professional career has included working as a Royal Society/NATO postdoctoral fellow at the Carlsberg Foundation, Copenhagen; lecturer (biochemistry) at Otago University, New Zealand; lecturer (biotechnology) at Dublin City University; visiting researcher at Case Western Reserve University in Cleveland; senior lecturer (microbiology) at the Dundee Institute of Technology; and reader (biotechnology) at the University of Abertay Dundee, Scotland. He is an active member of the Institute of Brewing & Distilling, American Society of Brewing Chemists, and Scottish Microbiology Society (as past convenor). He acts as an editor for Antonie van Leeuwenhoek, the International Journal of Wine Research, and the ASBC Journal. Walker is currently a professor of zymology at Abertay University, where he directs a yeast research group investigating growth, metabolism, and stress in industrial yeasts. Walker has published more than 100 articles in journals, books, and conference proceedings and has also authored the textbook Yeast Physiology and Biotechnology, published by J. Wiley (1998). He acts in a consulting capacity for international brewing, biofuel, and biotechnology companies.

Back to top

Dried yeast—Minimizing stress and maintaining viability
Chris Powell, Lallemand, Inc., Montreal, Canada
There are many applications for active dried yeast (ADY) in brewing, depending largely on the scale, type, and products of individual breweries. ADY uses include replacing propagated yeast, seeding propagators, fermenting small batches of beers, and bottle conditioning. Despite the range of applications, as well as other benefits such as long shelf life, until recently many brewers were reluctant to employ dried yeast for primary fermentations. This was often due to outdated beliefs surrounding the use of ADY in brewing, including the manner in which ADY should be rehydrated and its quality for use during fermentation. ADY producers have taken significant steps during the past 10 years to improve product quality, largely by introducing measures to prevent yeast stress. This presentation will describe some of the advances implemented during production to prevent cellular damage, and the simple precautionary steps brewers should take to maintain viability during rehydration.

Chris Powell obtained a B.S. degree in biology and environmental biology and subsequently moved to Bass Brewers (now MillerCoors) to work as part of the Research and Development team. Powell began his Ph.D. studies at Oxford Brookes University, in conjunction with Bass, and received his doctorate in 2001 on the subject of yeast cellular aging and fermentation performance. Subsequently, he became involved in a project funded by the European Commission, exploring mechanisms for the rapid detection of microbial contaminants within breweries. Powell joined Lallemand in 2004 and is currently in charge of genetic research and development for the identification and characterization of microorganisms utilized within the food and beverage industries, in addition to research focused on brewing yeast.

Back to top

Vitality/viability terms
Chris White, White Labs, San Diego, CA U.S.A.
This presentation will introduce the topics of viability and vitality and prepare participants for the advanced sessions to follow. Application of the material to small-scale craft brewing will also be discussed.

Chris White is the founder and president of White Labs Inc. White completed a Ph.D. degree in yeast protein chemistry from UC San Diego in the early 1990s. His interest in beer came from undergraduate studies at UC Davis, and after brewing beer at home throughout graduate school and collecting yeast strains, he started White Labs as a yeast and fermentation laboratory for brewers. White is also a faculty member at Siebel Institute of Technology in Chicago. He is a member of the Master Brewers Association of the America and the American Society for Brewing Chemists.

Back to top

Vitality/viability assays
F. Thiele, Radeberger Gruppe KG, Frankfurt, Germany; and W. Back, Lehrstuhl fuer Technologie der Brauerei I, TU Muenchen-Weihenstephan, Freising, Germany
The efficiency of brewing fermentation, as well as flavor development and other quality related issues, are directly related to the physiological condition of the yeast. There are two aspects describing the physiological condition of yeast: yeast viability and yeast vitality. Yeast viability is a measure of the number of living cells in a yeast batch. Yeast vitality is usually described as yeast activity, but since the yeast shows a large number of activities in the course of fermentation, this is not a clear definition. There have been several attempts to find a more suitable definition (e.g., a measure of yeast activity or fermentation performance, the ability to endure stress and still be able to perform its functions, fitness for use, etc.), but there has been no final definition with which everyone agrees. This demonstrates the complexity of the topic; it is not only a problem of finding a definition but also to measure the right parameter that indicates the overall physiological condition of living yeast cells. Viability and vitality are related, but they are not strictly correlated. Yeast batches can be found with high levels of dead cell that still show very high fermentation performance (e.g., often with batches from fermentations with higher temperatures), as well as batches with very high viability but with very poor fermentation performance (e.g., storage of yeast for long times at very low temperatures). The reference analysis for yeast viability is the plate count measurement. The major drawback of this method is the time needed. Therefore, other methods have been developed. Staining methods are predominantly used, including the industry standard methylene blue. Recently, a lot of work has been done in the field of fluorescent staining methods, and it has been shown that various reliable stains are available. Other methods for evaluating viability will be presented as well. The measurement of vitality is a very complex topic, and no standard methods have been developed yet. A broad variety of methods for the evaluation of yeast vitality has been developed over the years. In general the methods can be divided into two groups: the measurement of cellular components and the measurement of yeast activities. Various methods will be discussed in this presentation, and for some methods, a direct experimental comparison will be presented. For this comparison, yeast samples were artificially stressed with different stressors, and the results of different vitality measurements related to the fermentation performance of the yeast samples were determined. Finally, data on the influence of yeast vitality on the fermentation performance, as well as on the formation of yeast metabolites, will be presented using the intracellular pH measurement as an indicator of yeast vitality.

Frithjof Thiele completed an apprenticeship as a brewer and maltster at the Binding Brewery in Frankfurt, Germany, from 1993 until 1996. He studied brewing and beverage technology at TU-Munich-Weihenstephan and graduated in 2002. He worked on his doctoral thesis (“Influence of Yeast Vitality and Fermentation Parameters on Yeast Metabolites and Flavour Stability of Beer”) at the Lehrstuhl fuer Technologie der Brauerei I in Weihenstephan, finishing in 2006. During his time at the Chair for Brewing Technology I he was responsible for research and consulting in the field of yeast technology and fermentation, with national and international assignments. In 2008 he worked as a post-doc in the Department of Food and Nutritional Sciences, University College Cork, Ireland, and in 2009 he started work as a product and process developer for the Radeberger Group (the largest brewing group in Germany).

Back to top

Yeast vitality—A process approach
P. Bouckaert, New Belgium Brewing Co., Fort Collins, CO
Fermentation time and temperature profile consistency are important to produce consistent beer flavor. This study focuses on time consistency while keeping temperature profile the same. Screening of the relative importance of different variables was initially done through modeling of existing fermentation data. Models gave a better fit (r2) when yeast vitality data from the previous fermentation and yeast storage were used instead of current fermentation data, such as yeast count and methylene blue viability. The latter measurements failed upon measurement system analysis or gauge R and r within the range required in the brewery. The yeast count was replaced with yeast solid percentage after centrifuging. The key variable for predicting fermentation time was the rate of temperature increase in the fermentor. The most important parameter to control heat-up rate was the temperature in the fermented during filling. Other variables and interactions between variables included previous fermentation time and heat-up rate, cool-down rate of previous fermentation, yeast storage time, pitching rate, and (more for lagers) temperature of the environment. Two full factorial (two levels) designed experiments on knock out temperature and pitching rate showed that pitching rate could be used to reduce the standard deviation of fermentation time within the range tested. Variables affecting vitality were addressed in different ways. Cool-down rate of fermentations was resolved by reserving fermentors with high variability in cooling for aging only. Yeast storage time was addressed by guidelines and monitored. Previous fermentation time and heat-up rate became less variable in this process. Outliers on those two parameters can be yeast harvest selection criteria.

Peter Bouckaert studied biochemical engineering, with specialization in brewing and fermentation technology, in Ghent, Belgium. He was brewmaster for nine years at the Rodenbach brewery, worked in the Kronenbourg brewery, De Gouden Boom, and was involved with various distilleries, all in Belgium. He started his own brewpub, De Zwingel, in 1994. In 1996 Bouckaert changed course and became brewmaster for New Belgium Brewing Co. in Fort Collins, CO.

Back to top

Lyn Kruger has 30 years of brewing experience in yeast management, fermentation, sensory evaluation, laboratory services, and microbiology. She joined South African Breweries as a development microbiologist in 1978 and held various positions relating to yeast technology and research, microbiology, and analytical services. Appointed microbiology consultant in 1993, she was responsible for auditing, training, and development of microbiological standards for all SAB breweries. She emigrated from South Africa in 1995 to join the Siebel Institute of Technology in Chicago. She holds a B.S. degree in microbiology and chemistry from Rhodes University in Grahamstown, South Africa, and a M.S. degree in fermentation microbiology from the University of the Witswatersrand in Johannesburg, South Africa. She has published numerous articles in a variety of brewing journals. Kruger is currently president and COO of the Siebel Institute of Technology and is involved with all the various courses offered, laboratory services, yeast services, microbiological media, contract research, and consulting.

Back to top

Register