ETHANOL PRODUCING MICROORGANISMS Yeast

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ETHANOL PRODUCING MICROORGANISMSYeast Yeast
Management
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Introduction

• Module 4 Yeast Yeast Management
• Yeast Classification, Behaviour
• Yeast Management
• An exercise is given at the end of each Module
  and a certificate issued after successful
  completion of all modules

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Agenda

• Yeast
• What is yeast
• Yeast reproduction
• General requirements
• What is a pure culture?
• Yeast Characteristics
• Yeast Management
• (pitching, harvesting, storage, sampling,
  tracking
• Module 4 duration 3 hours
• 1 ½ hour presentation
• ¼ hour break
• ¾ hour group work
• ½ hour exercise

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Overview

• Yeast is not only the life force in beer, it is
  the single greatest flavor contributor. Brew a
  beer, split it in to two or more fermenters and
  pitch different yeasts.... you'll be a believer.

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Vocabulary

• ATTENUATION REFERS TO THE PERCENTAGE OF SUGAR
  CONVERTED TO ALCOHOL
• FINAL ATTENUATION REFERS TO THE END OF
  FERMENTATION
• FLOCCULATION REFERS TO SEDIMENTATION BEHAVIOUR IN
  YEAST
• ORIGINAL EXTRACT MEASURED DEGREE PLATO OF WORT
• APPARENT EXTRACT IS THE MEASURED DEGREE PLATO OF
  FINISHED BEER

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Yeast

• Introduction to Yeast Yeast Management

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Yeast - What is it?

• Yeast are unicellular fungi
• Individual cells are invisible to the naked eye
• Classification
• SACCHROMYCES CEREVISAE (ale)
• SACCHROMYCES UVARUM (lager)

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Yeast - REPRODUCTION

• IN BEER FERMENTATION YEAST REPRODUCES NON
  SEXUALLY BY CELL DIVISION
• BUDS ARE FORMED ON THE MOTHER CELLS AND AFTER ONE
  DAY THE NEW CELLS ARE SEPARATED FROM THE MOTHER

MOTHER CELL
START OF BUDDING
MOTHER WITH BIRTH SCARS DAUGHTER WITHOUT SCAR
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Yeast - REPRODUCTION
THE POINT HERE IS THAT WHILE INDIVIDUAL CELLS MAY
AGE, SINCE EVERY CELL GIVES RISE TO ONE WITHOUT
SCARS IT FOLLOWS THAT IN EVERY GENERATION
EXACTLY 50 HAVE NO SCARS
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Yeast General Requirements

• Rapid fermentation rate
• Efficient sugar utilization
• Ability to withstand stress imposed by alcohol
  concentrations
• Reproducible production of correct levels of beer
  flavour and aroma
• Desired flocculation character for the process
  used
• Good handling characteristics (viability, genetic
  stability

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THE EVILS THAT AFFECT YEAST

• Contamination from bacteria
• Death (as a living organism yeast cells die)
• Contamination from wild yeast (non cultured
  yeast)
• Sluggish yeast due to diet, environment, poor
  handling and storage procedures
• Abnormal behaviour (flocculance, fast settling
  are examples

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THE CHALLENGE- Maintaining a Healthy Strain

• The concept of a pure culture
• that is yeast free from contamination
• free from mutants
• pure strain (uniform yeast)

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Yeast Culture Practice

• Principle involves the isolation of single yeast
  cells- This is from a technique of dilution to
  get a single yeast cell
• In practice the method is to isolate single
  colonies on agar medium
• Pure culture supply (involves propagation at the
  brewery, central propagation system, purchase
  from supplier
• Yeast storage
• Propagation

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Yeast Culture Practice
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Yeast Culture Practice
TOP UP TO I BREW 800 HL
PROPAGATOR
PROPAGATOR
COMMERCIAL FERMENTER
8 hl at 15 oC For 2 days
200 hl in commercial fermenter at 15 oC For 3
days
40 hl at 15 oC For 3 days
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Yeast Characteristics

• The normal temperatures for lager yeast are (0
  13 oC)
• The normal temperatures for ale type yeast (13
  24 oC)
• It must be noted that fermentation rates is
  closely related to temperature. Typically the
  lower the temperature the slower the rate of
  fermentation
• pH ranges typically are 4.0 4.8
• Alcohol tolerances are up to 8 by volume
• In addition to alcohol production yeast produces
  three main by products that impact flavor
• Phenols (can give spicy , clove like and
  medicinal tastes)
• Esters (lend fruity tastes to beer)
• Diacetyl gives beer a butterscotch taste)

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Wild Yeast

• Any yeast that is not your culture yeast is wild
  yeast
• Wild yeast can produce the following
• Haze or turbidity
• Supper attenuation
• causing off flavours
• higher alcohol content
• Can be detected by
• microscopy
• Selective media
• Differential media
• Some are heat resistant
• Wild yeast controlled by CLEANING AND SANITIZING

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YEAST MANAGEMENT

• Bacteria and wild yeast are all around us and as
  a result some of that will get into beer.
• When given a chance good healthy yeast crowds out
  bacteria and also as it produces alcohol it makes
  it even more hostile for bacteria to grow
• Some of the more practical aspects of yeast
  management include Pitching, Harvesting and
  Storage
• By applying the following basic principles you
  can make your yeast healthy somewhat predictable

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YEAST MANAGEMENT- TRACKING

• Managing your data
• The easiest and least expensive part of yeast
  management is a good tracking system
• Include date of pitching
• Quantity pitched
• Yeast generation
• Fermenter that yeast came from for pitching
• Brew Number
• If acid washed YES/NO if yes record pH
• Cell count at pitching
• Viability

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YEAST MANAGEMENT- PITCHING

• Accurate pitch rates
• Underpitching will cause
• increased yeast growth, resulting in more
  production of by products like phenols, higher
  alcohols and other organic acids
• decrease alcohol production
• poor attenuation
• Sweeter-tasting beer
• Increases the risk of contamination by
  opportunistic bacteria or wild yeast

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YEAST MANAGEMENT- PITCHING

• Accurate pitch rates
• Overpitching will cause
• More sugars will be converted to alcohol
• Leads to excessive yeast autolysis
• This causes astringency in beer and yeast
  overtones in flavour (yeast bite)
• Older cells are present each time you over pitch
  because fewer new cells are being formed
• Increases a green beer character called
  acetaldehyde

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YEAST MANAGEMENT- SAMPLING

• Regardless of the method used for determining
  yeast pitching rates the brewer must ensure that
  a representative sample is used to do the test
• One way of reducing this is to pitch by weight
  rather than by volume
• The yeast is normally circulated/agitated prior
  to pitching to ensure homogeneity

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YEAST MANAGEMENT- SAMPLING

• Regardless of the method used for determining
  yeast pitching rates the brewer must ensure that
  a representative sample is used to do the test
• One way of reducing this is to pitch by weight
  rather than by volume
• The yeast is normally circulated/agitated prior
  to pitching to ensure homogeneity

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YEAST MANAGEMENT- HARVESTING

• The cone of a cylindro-conical fermenter is
  excellent for harvesting yeast.

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YEAST MANAGEMENT- HARVESTING

• Decanting of beer then harvesting from horizontal
  tank with using a yeast stick (screen of this
  yeast is sometimes done by passing it over
  vibrating screen to remove dead yeast and trub)
• Centrifugation is particularly useful for yeast
  strains that are not very flocculent

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YEAST MANAGEMENT- STORAGE

• Critical factors are
• Duration of storage (no longer than 3 5 days
• Temperature of storage (hold at temperature 0 4
  oC
• Method of storage(in clean sanitary vessels
• Leave yeast in fermenter with a thin layer of
  beer at 0 2 oC
• Store in yeast brink (this is optimal as the
  brink is equipped to maintain cold temperatures
  more effectively)
• Free from exposure to oxygen and bacteria

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YEAST MANAGEMENT- Acid washing

• Should never be considered as a cure for
  bacterial infection
• Theory of Acid Washing
• Lowers pH to the point at which bacteria and weak
  yeast cells are killed
• It often fails to kill all of the bacteria
  (merely reduces the number
• Acid washing reduces yeast viability
• ph is normally between 2 and 2.4

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YEAST MANAGEMENT- Rules Guidelines

• Never let anything that touches your beer touch
  the floor
• Always sanitize a sample valve or butterfly valve
  before and after using or taking a sample
• Avoid working in the cellar when a large amount
  of dust is being generated
• Clean and sanitize all hoses under pressure and
  replace ends of the hoses every year
• Check gaskets for defects or tears
• Before sanitizing all equipment that contacts
  beer must be cleaned of biological matter with a
  cleaner like caustic
• Alternate the use of acid and caustic cleaners to
  remove beer stone build-up
• Change sanitizers used in baths every day
• Work rapidly- to minimize exposure to non sterile
  environment e.g air
• Have spray bottle with 70 alcohol so you can
  quickly spray down and sanitize any surface
• Never allow free standing water or beer in your
  brewery because they provide ideal environment
  for bacteria growth

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YEAST MANAGEMENT- Yeast Room

• Brewers yeast should be kept in a cool (0 5
  0C) room, clean and free from contaminants,
  especially wort, and beer spoilage micro
  organisms
• Separate room for different strains if possible
  especially if they are bottom top fermented
  yeast
• Pipes should be placed 2 inches away from walls
  so that no soil is trapped
• Air ducts and cooling unit should be outside the
  room
• Room should be under positive pressure
• Floors should be sloped so as to drain properly
• All corners in the room should be rounded
• Condensation should not collect and harbour
  growth
• Pipes or other surfaces with temperature below
  the dew point should not be present
• Equipment and vessels should be elevated from the
  floor
• No grease or oils should be present
• Hose, paddles and fittings should be submerged in
  in a sterilizing solution
• Ideally authorization should be required for
  entry

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Summary

• Review
• Application
• Request feedback of training session

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Where to Get More Information

• Other training sessions-Brewing Fundamental
  Modules
• Books, articles, electronic sources
• e.g. Practical Brewer
• Consulting services, Brewers