Does yeast make a difference?

Posted on 8th July 2022

At The Malt Miller, we stock well over 300 varieties of yeast. But what’s the difference between all these strains? Surely one type can’t be that different to another… can it?

What is yeast, anyway?

Yeast is an extraordinarily widespread microorganism, with hundreds of known species. It grows in the wild on flowers and fruit and spreads by contact with pollinators like bees and even on the wind – so you could literally find yeast in the air around you.

The yeast we use for brewing is almost always a species called Saccharomyces cerevisiae. This species is incredibly versatile thanks to its ability to ferment sugar, turning it into ethanol – pure alcohol – and carbon dioxide. This same species is used for everything from brewing to baking bread, as well as making just about any alcoholic drink you can think of.

Dried yeast

Even though it’s all the same species, there can be big variations between different strains of Saccharomyces. It’s a bit like dogs: all domestic dogs are the same species (Canis familiaris), but you wouldn’t mistake a Great Dane for a chihuahua! In the same way as dogs can be bred for specific purposes, such as scent tracking or running speed, different strains of Saccharomyces are optimised for different purposes.

Spot the difference

You might expect a difference between a yeast for making wine and another for brewing beer – they have to ferment different types of sugars – but there are many variations within beer yeast.

Some of the key differences are:

How “hungry” the yeast gets – i.e. how much sugar is left over at the end of fermentation. A “high attenuating” yeast will finish at a lower gravity, with less leftover sugars, than a “low attenuating” yeast.

How well the yeast falls out of suspension. Very “flocculant” yeasts clump together and drop to the bottom of the fermenter, leaving clear beer. By comparison, wheat beer yeasts tend to stay in suspension, giving the characteristic cloudy appearance.

All yeasts have an ideal temperature range where they produce their best flavours. For many lager yeasts, this is between 10°C and 14°C, whereas most ale yeasts prefer closer to room temperature (usually around 20°C).

Some yeasts like it much hotter! Belgian saison yeasts are happy above 28°C, while kveik strains excel at temperatures nearer “blood temperature” – 37°C!

Yeast produces ethanol (pure alcohol) as it ferments, but alcohol can kill many microorganisms, yeast included – just like in alcohol-based hand sanitiser. All yeast strains have a limit to how much alcohol they can take before they go dormant to prevent drinking themselves to death (!), usually around 8-10% ABV. Special varieties of yeast can take more alcohol and are suited to extra-strong beers like imperial stouts.

More than numbers

Beyond those basic statistics covering how a yeast strain goes about fermentation, there are lots of differences in the final flavour, such as:

  • Beer colour and clarity
  • Head retention
  • Final pH
  • Sweet/dry flavour
  • Mouthfeel (thin/full)
  • Perception of alcohol (hidden/prominent/hot)
  • Yeast aroma (peppery/fruity)
  • Hop expression
  • Malt expression

The proof’s in the pint

There’s no better way to discover those differences than with a practical experiment!

We decided on a simple malt and hop bill, using a 50/50 mix of pale malt and pilsner malt and a single hop – Summit – to help highlight the yeast contribution to the final beer.

We then brewed up a 40L batch of wort on a Grainfather G40 and split the wort between two fermenters. The new split batch feature in the Grainfather recipe builder app makes all the calculations a breeze!

One fermenter was given Mangrove Jack’s M36 “Liberty Bell” yeast, which gives “light, delicate fruity esters and helps to develop malt character”.

The other fermenter got Mangrove Jack’s M66 “Hophead” yeast. This strain is specially designed to promote a hop forward, fruity profile, and includes an enzyme that breaks down hop oils to help release more aroma and flavour.

After fermentation was completed, we kegged both beers and carbonated them to the same level. Then came the best part – the taste test!

Even having explicitly designed this experiment to show the differences between the two yeasts, we were surprised just how much difference there was! These were like two different beers, with differences all the way from appearance in the glass, through to aroma, flavour, and mouthfeel and finish.

As well as showing us the massive contribution of yeast to the final beer, this was also a great way to learn what the hops and malt brought. The Summit hops we used really shone across both beers, and as different as they were, they were both delicious!

If you want to try our experiment for yourself, you can pick up the comparison recipe kit, which includes both yeasts. If you like the sound of either beer by itself, we’ve got kits for each of the Liberty Bell and Hophead recipes.

You could also create your own yeast comparison kit with our recipe generator. Let us know how your brew goes  – we love hearing about your beers!

Check out our video showing the full brewing and tasting of our yeast comparison experiment, and remember to subscribe to our YouTube channel for all the latest brews and reviews from The Malt Miller.

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