Biotechnology of Brewing Brewing Processes

1
Biotechnology of Brewing Brewing Processes

• Lectures 2-3

2
Overview of the Brewing Process
Malt Delivery
Mill
Water
Mashing
Adjuncts
Lautering
Wort Boiling
Yeast Propagator
Spent Grain / Hops For Animal Feed
Wort Clarifying and Cooling
Yeast Storage
Fermentation
Yeast Recovery
Air
Maturation
Clarification CO2 Saturation
Packaging
3
Malting

• Malting refers to the process of activating
  germinating and roasting barley
• Malting is a process now generally performed by
  large breweries or more commonly specialised
  malting companies
• Barley is cleaned, sized, viability measured and
  nitrogen content determined prior to malting
• rodent dropping and insect infestations removed
• Barley sizing is important to ensure even
  germination
• Different varieties malted separately
• First step in malting is the activation of
  enzymes within the barley
• Process called steeping
• Addition of cool water for 2-3 days, which is
  changed regularly (removes microbes, ? DO)
• Removal of microbes essential for malt stability
• Respiration of barley increases therefore O2
  demand rises (anaerobiosis -gt alcohol -gt toxin)

4

• Post steeping - germination
• Barley spread thinly in a germination box and
  turned regularly to dissipate CO2, keep
  temperature constant, and prevent roots from
  matting
• Embryo activated - catylases dissolve wall of
  endosperm
• Enzymes secreted by the developing embryo result
  in modification - malted barley can be referred
  to as under, well or over modified
• Germination is completed once barley root is
  approximately 2/3 length of husk
• The processes of steeping and germination can be
  combined and a continuous process evolved
• Dormancy
• Profound dormancy (embryos temporarily unable to
  germinate)
• Water sensitivity - barley germinates only if not
  submerged

5

• Biochemistry of Malting
• Numerous proteases are present (breakdown
  proteins -gt AAs)
• Starch the most important material
• Occurs in two forms, amylose and amylopectin
• Glucose polymers consisting of 1000-4000 Glc
  units
• During germination barley starch degraded into
  polyglucose molecules
• Enzymes involved include ? glucosidase, ?
  amylase, ? amylase and debranching enzymes
• After kilning only ? amylase, ? amylase
  activity remains
• Two most important enzymes during malting
• ? amylase
• Cleaves starch randomly (except near ends or
  branch points)
• Produces mainly dextrin molecules
• Requires calcium for optimal activity
• Conditions, pH 5.5, temp 700C
• Not present in mature barley, forms during
  germination
• More thermostable than ? amylase
• ? amylase
• Cuts off maltose from non-reducing ends of
  molecules
• Produces ? maltose (major sugar in wort)

6

• Other compounds liberated during Malting
• hemicelluloses and gums (10 weight of barley
  from endosperm cell walls i.e. ? glucans
  (glucose polymers) are undesirable in large
  quantities
• Precipitate during fermentation --gt jelly
• Must be degraded to products soluble during
  brewing
• Fats (3.5)
• Unsaturated fatty acids most important --gt cell
  wall synthesis of yeast during fermentation
• Phosphates (1)
• phytic acid - a hexaphosphate of inositol (Vit B)
• Degraded by the yeast to produce myoinositol and
  phosphoric acid
• Germination is arrested by drying kilning the
  barley
• reduces moisture content (45 -gt 5)
• Imparts colour to malt - higher temperatures used
  to produce dark coloured beers
• Malt is then graded and sold to brewery
• All these process result in a malt that can be
  readily converted into the fermentation medium
  required by the brewer.
• The following steps are thus typically carried
  out on site to produce the wort (sugar medium)
  used by the yeast to produce beer

7
Milling

• Process in which malt is ground into meal or
  grist, or gritty flour
• Important to keep barley husk relatively intact
  as they are needed during wort recovery
• Endosperm fragments are however required to be
  small to ensure rapid degradation
• Two types of mills
• dry mills
• wet mills - addition of water prior to milling
• wet mills inflict less damage on the malt
• Grist then pumped / gravity fed into mash-tun

8
Mashing

• Grist sprayed into mash-tun along with water
  (doughing-in)
• Heat applied to mash (65-670C)
• ? amylase and ? amylase continue to degrade
  starch molecules into more readily fermentable
  sugars and dextrins
• Mash conditions favour one or the other enzyme
• Control of mashing conditions through using
  profiles enables brewer to produce vastly
  different worts
• Two types of mashing
• Infusion mashing
• heating of mash is relatively constant throughout
  the process
• generally used for top fermenting worts
• Decoction mashing
• heating of mash is achieved by removing portion
  of mash to separate vessel, heating and returning
• Results in stepwise increase in temp

9

• Decoction results in optimum tempertures being
  reached for
• proteolysis (40-540C)
• starch hydrolysis (54 - 650C)
• Wort separation (730C)
• Some breweries use a mixture of the systems
• Changing conditions of mash as mentioned large
  changes in wort
• Wort is then extracted from the mash-tun (or
  through a separate larger SA vessel called a
  lauter tun) through filtering through the husks
  of the barley
• Wort produced 1.060 - 1.100 SG
• However this is diluted due to sparging of water
  through the husks
• Spent grains sent for animal feed
• Solid adjuncts added at this stage of brewing
• Double mashing
• Process as described but with an additional
  cereal cooker which is used to hydrolyse maize or
  rice grists
• Mashing process begins as usual with the
  subsequent addition of adjunct later in mashing
  cycle when temperature is highest
• Used in production of American worts
• Temperature programming of mash also used

10
Wort Boiling

• Sweet wort brought to the boil in large kettles
  (or coppers)
• Principle effects
• arrest enzyme activity
• sterilise wort (at least partially)
• coagulate proteins and tannins (removed as trub)
• precipitation of calcium phosphate, ? pH
• distillation of volatile compounds
• evaporation of H2O, ?concentrate wort
• colour production, caramelisation, oxidation of
  tannins (colour of final product controlled at
  this stage)
• if a very dark beer is required caramel can be
  added at this stage
• extraction of bitter residues from hops
• essential oils infused
• iso ? acids improve beer foam (from hops)

11

• Dissolved matter within the wort is called
  extract (and expressed in oPlato)
• hot break - hop residues removed via strainer
• cold break - lt600C protein precipitate - trub
• Addition of finings during kettle boiling
  enhances trub removal (haze)
• Further trub removal occurs though either
  filtration or centrifugation (whirlpool)
• Trub produced during wort boiling - 30-60 g/hl
• Kettle boiling isomerises the humulones to
  isohumulones and allo-isohumulones
• humulinic acid has little bitter taste
• Wort is then cooled (plate heat exchangers) and
  aerated before transfer to fermentation vessels
• Oxygen is required as a growth factor during
  anaerobic fermentation
• Used to synthesise unsaturated fatty acids and
  sterols for the membrane
• Yeast added to fermentation from propagation
  facility

12
Fermentation

• Clarified, aerated wort is pitched (inoculated)
  with approximately 10 million cells per ml
• Metabolism of substrates occurs via pathways
  previously discussed
• First fermentation stage is termed primary
  fermentation this stage continues until SG levels
  off (or in brewing terms the beer has attenuated)
• 24-48 hours after pitching clumps of foam
  (kraüsen) appear
• Yeast will double in mass during ale production
  and quadruple in mass in lager
• Process time 3-5 days for ale and 8-10 days for
  lager
• Once beer has attenuated the yeast is removed
  (lager) by cone cooling (00C) and the beer left
  or pumped to maturation tanks
• Beer at the end of this stage is referred to as
  green beer

13

• Continuous fermentation
• A process developed here in New Auckland in the
  late 50s and early 60s through collaboration
  between Lion and DB breweries (Morton Coutts)
• Almost all NZ beer was at one stage produced by
  this method
• DB breweries currently one of the only breweries
  world-wide to be producing beer by this method
• Two major types of continuous process
• Cascade Method
• A series of stirred tanks into which wort is
  introduced and flows up and out into the next
• Degree of attenuation is a function of
  temperature, dwell time, strength of the wort R
• Recycling of yeast enables higher flow rates
• Dwell time 25-30 hours
• Plug flow reactor (tower fermenters)
• Use of strongly bottom flocculant yeast
• Wort pumped up through the yeast
• Flow rate adjusted such that wort reaching top
  of vessel is correctly attenuated
• Now used primarily in vinegar production
• Operating costs significant reduced
• Process however susceptible to infection
  (lactobacillus) and brewery limited to production
  of one beer although beer is generally very
  consistent
• Equilibrium time 2-3 weeks
• Possible to run fermenter for over 9 months

14
Maturation - Aging and Finishing

• Secondary fermentation - yeast that did not
  settle during cone cooling converts harsh
  flavours
• For example diacetyl --gt 2,3 butanediol (burnt
  butterscotch flavour to a flavourless compound)
• Aging of beer at 00C helps with formation of
  large protein-tannin complexes which impact on
  beer stability
• As these form at low temperatures they can
  effectively be removed by filtration
• If secondary fermentation not required the beer
  is
• filtered (diatomaceous earth) and clarified
• Carbonated with CO2 recovered during fermentation
• Additional flavours, caramels added to produce
  the desired product
• hop extracts added to raise bitterness levels
• caramels to enhance colour
• antioxidants (oxidation reduces shelf life of
  beers)
• Finished beer then sent to packaging line