Craft Brewing 101: The Yeast We Can Do
The Yeast We Can Do
There are many kinds of yeast everywhere around us. In the air, on your face and in the supermarket fridge. Microscopic organisms involved in the production of bread, cakes, doughs, pizza and, of course, beer. Yeast is alive. It metabolises, breathes and transforms. It takes the sugars from malt and converts them into alcohol, carbonation and the aromatic compounds that shape a beer’s character.
A very old relationship
Humans have worked with yeast for more than 5,000 years, long before they understood what it was.
From early breads to farmhouse ferments, yeast acted as an unseen biological partner.
Only within the last couple of centuries have we understood yeast as microbiology rather than mystery. Living cells responding to temperature, nutrients and handling. That knowledge transformed brewing.
Today, brewers work with hundreds of distinct strains. Each strain behaves differently, produces different flavours and helps define specific beer styles.
Two main brewing yeast types
Now let’s get scientific.
Brewing relies primarily on two species:
Top fermenting yeast (Saccharomyces cerevisiae)
Warmer fermentation temperatures
Produces expressive fruity esters
Used for pale ales, IPAs, stouts, Belgian styles and many modern ales
Bottom fermenting yeast (Saccharomyces pastorianus)
Cool fermentation temperatures
Produces clean, subtle flavour profiles
Used for pilsners, Helles, bocks and classic lagers
Temperature has major influence.
Warm fermentation increases ester formation.
Cool fermentation reduces esters and produces a cleaner profile.
Take a beer like 45 Days Lager. Its name reflects the slow fermentation and extended cold conditioning that allow lager yeast to create a crisp, refined result.
How yeast works
When yeast meets oxygenated, sweet wort, several things happen:
• It consumes fermentable sugars
• Produces alcohol and CO₂
• Synthesises esters that bring fruit-like notes
• Creates phenols only in specific strains, such as Belgian or wheat beer yeasts
• Shapes mouthfeel, dryness and balance
Some strains create stonefruit.
Some lean peppery or spicy.
Some stay nearly invisible, letting the malt and hops speak.
Harvesting and reusing yeast
Yeast can be reused many times, a practice known as harvesting.
Once fermentation finishes, we collect healthy yeast and pitch it into the next batch.
It reduces waste and helps maintain consistency across similar beers.
Because yeast is alive, every generation changes slightly due to natural variation and stress. Brewers therefore monitor:
• viability
• cell count
• health
• performance across batches
When it is time to begin again
We handle yeast with care. Depending on its health and count we keep a strict outline for how many generations we use in different batches of wort, and checking viability is part of our daily routine.
Eventually, a yeast culture reaches its limit.
Brewers then start again with a preserved sample from a yeast bank.
Growing this culture into a full pitch is called propagation.
Over several stages, the culture is given oxygen and nutrient rich wort, allowing it to multiply into millions of healthy cells.
Under the microscope, brewers look for new buds forming on mother cells, a sign of active growth.
Propagation determines the flavour, stability and success of the beer that follows.
The little magician
Yeast is both predictable and surprising.
Trained strains reliably produce specific flavour profiles, yet small shifts in temperature, oxygen or nutrients can change fermentation outcomes.
Give it proper care, and it delivers.
