Lesson 1 - Introduction to Fermentation

This section provides an overview of what we will study in the lessons.

During the unit we will learn how to: 

● Draw a diagram that shows the main phases in a typical brewery fermentation and describe what is happening at each stage.

Figure: Stages in fermentation

● Describe, with suitable drawings, changes during fermentation in wort gravity, dissolved oxygen, pH, free amino nitrogen, CO₂, and yeast concentration.

● Give a mass balance of fermentation.   

● List the key features that are used to assess the successful outcome of fermentation.

● List the major fermentation variables and describe how they influence fermentation progression and performance.

● Describe the practice of high gravity brewing and discuss the reasons for its adoption by many brewers.

Figure: Schematic showing process steps for high gravity brewing

● Discuss the various ways in which yeast influences beer flavour.

● List the major groups of compounds produced by yeast as it grows on wort and transforms it into beer and give typical concentrations at which they arise.

Table: Major flavour-active groups of compounds produced by yeast in fermentation

Alcohol (ethanol)

CO2

Organic acids

Aldehydes

Fatty acids

Higher alcohols (fusel alcohols)

Esters

Sulphur compounds

● Describe the metabolic pathways used by yeast to form the major groups of yeast-derived flavour compounds and discuss why they are present.

Figure: Relationships between formation of flavour compounds and intermediary metabolism

● Describe how spontaneous fermentations are carried out and give examples of beer styles in which they are used.

● Discuss the microbiology of spontaneous fermentations and describe some of the unusual fermentation products formed.

● List the requirements of fermentation vessels for the production of beer.

● Describe the materials used to construct fermentation vessels and assess their strengths and weaknesses.

● Describe, with suitable drawings, the design of fermentation vessels suitable for both top- and bottom-cropping yeast strains.

 

Table: Properties of some closed-design fermenting vessels

Type	Comments
Closed box	● Inexpensive to build ● Can be stacked on separate floors of a building ● Yeast crop retained by upstand but difficult to remove ● Poor draining properties
Horizontal cylinder	● Relatively inexpensive ● Avoids tall hydrostatic head ● Difficult to empty and remove yeast crop ● Can be stacked to minimise footprint
Vertical cylinder	● Relatively inexpensive ● Easily arranged in tank farms ● Efficient cleaning ● Good draining properties ● Cropping not as efficient as coned vessels
Spheroconicals	● Excellent mixing ● Most efficient design for external cooling ● Efficient cropping ● Very expensive to build

Figure: Principal features of a cylindroconical fermenter

● Understand the requirements of fermentation rooms for use with top and bottom yeast cropping.

● Identify the selection criteria used to choose fermenter numbers and capacities. 

● Describe practices used during fermenter fill and discuss methods of wort cooling, pitching, and aeration or oxygenation.

● Describe how fermentations are controlled.

● Discuss the process of combined fermentation and cold conditioning and compare the advantages and disadvantages of this approach with those of a two-tank approach.

● Understand the theory that underpins continuous fermentation.

Figure: Illustration showing the principle of a chemostat

● Critically assess the benefits and drawbacks of continuous brewing fermentation.

● Describe continuous fermentation systems developed for commercial brewing.