Beer Brewing – Comprehensive Study Notes

Overview / Context

• Lecture date: June 27 2025; focus: Beer brewing as a case-study of large-scale fermentation.

• Beer production = one of the oldest and largest global biotechnology industries.

• Bridges earlier lecture on large-scale cell culture → real-world industrial example.

• Emphasis throughout: Identify where enzyme catalysis, microbial physiology, and process engineering intersect.

What Is Beer? Key Sensory Attributes

• Carbonated, alcoholic beverage (but note low & 0-Alc variants).

• Visual markers

  • Colour span: very pale → amber → deep brown/black.

  • Persistent foaming head distinguishes beer from most other drinks.

  • Liquid clarity varies: bright → protein/yeast haze → intentionally cloudy styles.

• Taste/aroma

  • Bitterness from hop iso-α-acids.

  • Floral/citrus/herbal notes from hop oils + minor yeast metabolites (higher alcohols, esters).

  • Mild acidity because dissolved CO2 ↔ H2CO_3.

Legally Defined Ingredients (German Purity Law – Reinheitsgebot, 1516)

1. Water.

2. Malt (almost always malted barley, occasionally wheat, rye, oats, etc.).

3. Hops (whole cones or processed extracts).

4. Yeast (Saccharomyces cerevisiae – “ale” strains; S. pastorianus – “lager” strains).

• Worldwide practice allows extra fermentables ("adjuncts" = cane sugar, corn, rice syrup), fruits, herbs, exogenous enzymes (e.g. β-glucanase) for process aid or flavour.

Global Market Snapshot

• Annual value: >$700 billion (figure slightly dated, still indicative).

• Largest producer volumes: China > USA.

• Highest per-capita consumption: Czech Republic (long-standing #1).

• Growth niches (last 10–15 y): craft breweries, non-/low-alcohol beers.

Process Flow – Bird’s-Eye View

Water + Malt + Hops + Yeast (+Adjuncts/Enzymes)
        ↓
Milling → Mashing → Lauter/Word Recovery → Wort Boil (add hops) → Whirlpool/Clarify → Cool & Aerate
        ↓
    Fermentation (Ale or Lager)  ↘CO2        ↘Excess Yeast
        ↓                                   (Vegemite, extracts)
Maturation → Filtration/Clarification → Packaging (bottle/can/keg)
    ↓                                     ↘Pasteurise (in-package or flash)
 Waste streams (spent grain, trub) → Animal feed, disposal

• Everything prior to fermenter = “upstream”.

• Product polishing & packaging = “downstream”.

• CO₂ co-product captured as food-grade gas for beverage dispense, carbonation, etc.

Water Management

• Beer ≈ 90\text{–}98\% water → sensory & process impacts huge.

• Treatments employed:

  • Adjust hardness (Ca²⁺, Mg²⁺) → influences mash pH, enzyme activity, flavour.

  • Particle filtration + UV sterilisation when microbial load questionable.

  • In high-gravity brewing the dilution water is pre-carbonated with reclaimed CO_2.

Malt: Source & Pre-Processing

• “Malt” = barley grain steeped → germinated → kilned.

  • Steeping: hydrate to ~45\% moisture.

  • Germination (3–5 days): enzyme synthesis (α- & β-amylase, protease, β-glucanase).

  • Kilning: stops growth, sets colour/flavour (Maillard reactions) → scale of heat = colour spectrum (pilsner → crystal → chocolate → black malt).

• Trade-offs: Darker kilning = richer flavour/colour but denatures more endogenous enzymes → necessitates blend of pale + specialty malts.

• Grain received at brewery is first milled/cracked to expose endosperm while keeping husk mostly intact (acts as filter aid later).

Mashing (Slurry Bioreactor)

• Goal: convert insoluble starch → fermentable sugars + extract proteins/minerals.

• Operations

  1. Mix milled malt (plus solid adjuncts) with hot liquor (brewing water) → porridge-like mash.

  2. Temperature schedule (typical):

  • 35\,°\text{C} – β-glucanase window (cell-wall breakdown).

  • 45\,°\text{C} – protease rest (AA/peptide formation, foam & clarity control).

  • 62\text{–}66\,°\text{C} – β-amylase (maltose generation).

  • 70\text{–}72\,°\text{C} – α-amylase (dextrin reduction, body).

  • 75\,°\text{C} mash-out (stabilises composition, lowers viscosity).

• Enzyme provenance: exclusively from malt unless brewery supplements with commercial enzymes (common in high-adjunct recipes).

Lautering / Wort Recovery

• Equipment: Lauter tun or mash filter.

• Husk bed forms self-filter; sweet wort drawn off under slight vacuum or by pump.

• “Sparging” = showering grain bed with 75\,°\text{C} water to rinse residual sugars → increases brewhouse yield.

• Solids generated: Spent grain (protein-/fibre-rich) → cattle feed.

Wort Boil – Multiple Roles

• Carried out in kettles (copper or modern stainless). Typical 60–90 min vigorous boil.

• Functions

  1. Sterilise wort.

  2. Precipitate hot break (protein denaturation, tannin complexes).

  3. Evaporate undesirable volatiles (e.g. DMS from precursor S-methyl-methionine).

  4. Isomerise α-acids from hops → bitterness.

  5. Concentrate wort (≈8 % volume loss).

• Hop scheduling

  • Early additions (“bittering hops”) – maximise iso-α-acid yield.

  • Late/whirlpool additions (“aroma hops”) – preserve volatile terpenes.

Whirlpool Clarification

• Tangential inlet sets fluid into rotation; solids migrate to centre “trub cone”.

• Clear wort drawn from periphery bottom outlet.

Wort Cooling & Aeration

• Heat-exchanger cools to fermentation set-point (ales 18\text{–}22\,°\text{C}, lagers 8\text{–}15\,°\text{C}).

• Only time oxygen is wanted: injected/sterile-air-sparged to ~8\text{–}10\,mg\,L^{-1} O₂ to permit fatty-acid/sterol synthesis for yeast membranes.

Yeast Handling & Pitching

• Strain choice shapes beer style:

  • Ale (S. cerevisiae): top-cropping, ester-forward, warmer & faster (≈3–5 d).

  • Lager (S. pastorianus): bottom-settling/flocculent, clean profile, cooler & slower (≈7–14 d).

• Inoculum sources

  1. Serial repitching: harvest cone yeast, acid-wash (~pH 2) → reuse 3-10 cycles until genetics or contamination drifts.

  2. Pure-culture propagation: if contamination rises or strain refresh required, work back from cryostock.

Fermentation Vessel & Dynamics

• Cylindro-conical tanks dominate; internal agitation = CO₂ lift only.

• Key constraints

  • Optimal metabolic temp < optimal growth temp (high temps → off-flavours).

  • pH naturally falls to ~4.0\text{–}4.5 → suppresses pathogens.

  • Ethanol tolerance critical; brewing strains withstand \sim10\text{–}15\%\,(v/v).

• Stoichiometry core:
  \mathrm{C6H{12}O6 \;\rightarrow\; 2\,C2H5OH + 2\,CO2}
  ⇒ 1 mol ethanol ↔ 1 mol CO₂ (minimum; biomass diverges some carbon).

• Typical time-course (≈4 d ale):

  • Monosaccharides (glucose, fructose) disappear first (<36 h).

  • Maltose exhausted by ~60 h.

  • Maltotriose partly remains → residual body/carbs.

  • Yeast growth peaks then flocculates; ethanol plateaus.

Maturation (Conditioning)

• Cold storage (lagering) 0\text{–}4\,°\text{C} for days–weeks.

  • Smooths flavour (diacetyl reduction), clarifies via further yeast/protein precipitation, increases CO₂ absorption.

Clarification & Stabilisation

• Filtration media: kieselguhr (DE), sheets, membranes.

• Additives occasionally used: PVPP (polyphenol binding), silica gels (protein haze control).

• Pasteurisation options

  1. Tunnel – bottles/cans heated ~60\,°\text{C} for prescribed “pasteurisation units”.

  2. Flash – heat to 71\,°\text{C} for ~15 s, then package aseptically (common for kegs).

• Note: Pasteurisation ≠ sterilisation; just lowers bioburden for shelf-life extension.

Packaging Routes

• Bottles (amber/green glass limits light-struck "skunk" reactions of hop compounds).

• Aluminium cans (light-tight, lightweight, recyclable).

• Stainless kegs for draught; product flash-pasteurised inline.

Co-Products & Waste Streams

• CO₂ (food-grade) – captured, compressed, reused/sold.

• Spent grain/trub – high protein & fibre → cattle feed; emerging valorisation (biogas, protein isolates).

• Surplus yeast – processed into spreads (e.g. Vegemite/Marmite) or nutraceuticals.

• Effluent (wort kettle condensate, cleaning-in-place solutions) must meet discharge regulations; breweries integrate anaerobic digesters.

Special Topic: 0- and Low-Alcohol Beer

• Consumer demand growth ⇒ technological innovation.

• Methods

  1. Vacuum distillation – lower boiling point of ethanol.

  2. Reverse osmosis – membrane separates ethanol + aroma condensate from water; re-blend sans alcohol.

  3. Biological – use non-traditional yeasts (e.g. Torulaspora delbrueckii) or limit fermentable sugars to keep <0.5\% ABV.

  4. Process tweaks – arrested fermentation, dealcoholisation post-ferment.

• Challenge: maintain body, foam, hop aroma once ethanol removed.

Product Stability / Quality Risks

• Light exposure → hop iso-α-acids + riboflavin → MBT (“skunky”) – mitigated by brown glass/cans.

• Oxygen pickup post-ferment → stale cardboard flavours (trans-2-nonenal).

• Low pH, ethanol & hop iso-acids impart natural microbial hurdle; yet Lactobacillus & wild yeasts can still spoil if hygiene lapses.

Biotechnology Principles Reinforced

1. Enzyme technology – endogenous vs. commercial additions; temperature/pH optimisation.

2. Microbial physiology – oxygen requirements, ethanol tolerance, contamination control.

3. Stoichiometry & kinetics – sugar utilisation hierarchy, product yields, growth-associated vs. non-growth-associated metabolism.

4. Process integration – upstream media prep ↔ fermentation ↔ downstream clarification & packaging.

5. Sustainability – CO₂ capture, by-product valorisation, water reuse.

Connections to Earlier/Future Lectures

• Parallels with pharmaceutical cell culture: sterility demands, scale-up constraints, media design (C:N balance).

• Enzyme immobilisation & industrial proteases – concepts transferable to detergent, dairy industries.

• Bioreactor design fundamentals (mass transfer, heat removal) reappear in bioethanol, kombucha, kimchi, etc.

Ethical / Practical / Societal Implications

• Public health: responsible drinking campaigns, non-alcoholic options broaden inclusivity.

• Regulatory compliance (e.g., Reinheitsgebot, excise taxation) affects formulation freedom.

• Environmental stewardship: breweries adopt circular-economy practices (spent grain → food/energy; CO₂ capture) to reduce footprint.

• Cultural heritage: brewing traditions (Czech, German, Belgian) illustrate intersection of science & societal identity.

Numeric / Statistical References & Key Figures

• Beer global value: >$700 Bn.

• Composition: 90\text{–}98\% water.

• Cytology: Yeast optimum growth 30\text{–}35\,°\text{C} but quality demands cooler fermentation (ales 18\text{–}22, lagers 8\text{–}15).

• CO₂ : Ethanol stoichiometry 1:1 molar (see equation above).

• Fermentation timeframes: ales 3–5 d, lagers 7–14 d + conditioning.

• Pasteurisation: ~60\,°\text{C} for 20–30 min (tunnel) or 71\,°\text{C} for 15 s (flash).

Exam Pointers / Must-Know Takeaways

• Identify four core ingredients & their biochemical roles.

• Be able to sketch/annotate the full brewing process flow with upstream & downstream steps.

• Explain how mash temperature profile tailors fermentable vs. non-fermentable sugar spectrum.

• Write balanced fermentation equation and relate to co-product capture.

• Contrast ale vs. lager fermentation in terms of yeast, temperature, flavour output.

• Describe at least two technologies for producing low/zero-alcohol beer.

• Discuss how hop compounds contribute to both flavour and microbial stability.