Splitting one batch of wort between two yeast strains
Yeast shapes flavour more than most new brewers expect. Splitting one batch of wort between two strains shows you exactly how much. The trick is keeping everything else the same.
One wort, two beers
Pour the same wort into two fermenters, pitch a different yeast into each and you will end up with two different beers. One may be clean and crisp, the other fruity and round. Nothing else changed, so every difference you taste came from the yeast.
That makes a split batch the best yeast lesson available to a homebrewer. It costs one brew day and a second fermenter. Reading descriptions on yeast packets teaches you far less than tasting the result next to its twin.
Choosing two strains worth comparing
Pick strains that differ in a way you want to understand. Some pairs that teach a lot:
- A clean American ale yeast against an English ale yeast. The English strain usually gives more fruity esters and a softer finish.
- A neutral ale yeast against a German wheat beer yeast, which gives banana and clove from the same wort.
- A clean ale yeast against a kveik strain. Kveik ferments cleanly at 30 °C and above, which suits an Indian kitchen in summer.
Read the attenuation and temperature range on each packet before you choose. If one strain is rated for 18 to 22 °C and the other for 12 to 15 °C, you cannot ferment them side by side fairly without one running outside its range.
Avoid comparing two clean strains first. The difference can be too subtle to learn from until your palate is trained.
Splitting the wort fairly
Fairness is everything. Brew one batch, chill it, then split it evenly by volume into two clean, sanitised fermenters of the same type. Use a measuring jug or marks on the fermenter. If one vessel gets the clearer wort from the top and the other gets the trub from the bottom, you have added a second variable.
Aerate each half the same way, for the same time. Take one gravity reading for the whole batch before you split. Label each fermenter clearly with the strain and the date. Two identical buckets look very alike after a week.
Pitching the right amount for each half
Each half is now its own batch. For a 20 litre brew split in two, each fermenter holds 10 litres. A standard 11.5 g sachet of dry yeast is sized for about 20 to 23 litres of ordinary strength wort, so half a sachet, weighed on a kitchen scale, suits each 10 litre half. Our guide on how much yeast to pitch covers liquid yeast and stronger beers.
Rehydrate dry yeast if the maker recommends it, in a little sterile water at the temperature on the packet. Treat both halves the same way. Pitch them within a few minutes of each other so neither wort sits unpitched for longer. A half that sits warm and unpitched for an hour gives any stray bacteria a head start, which is a third variable you do not want.
Underpitch one half and overpitch the other and you are partly testing pitch rate. Keep the cells per litre roughly equal.
Keeping the temperature the same
Temperature changes yeast flavour as much as strain does. Ferment both halves side by side, in the same place, at the same temperature. A tub of water with both fermenters standing in it keeps them within a degree of each other.
The kveik pairing is the exception. Kveik wants 30 °C or more while a clean ale yeast wants 18 to 20 °C. In that case you are comparing each yeast at its best, not at the same temperature. Say so in your notes.
Tasting the two blind
Package both the same way on the same day and give them the same conditioning time. Then taste them side by side. Better still, ask someone to pour them into identical glasses marked only underneath, so you do not know which is which.
Smell first, because yeast character shows strongest in aroma. Note fruit, spice, sulphur and anything solvent-like. Then taste for dryness and body, since strains differ in how far they ferment. Compare final gravities too: a strain that finishes two or three points lower will taste drier. Our guide to beer off-flavours helps you name what you find.
What a split batch teaches you
After one split batch you will never read a yeast description the same way. After three you will start choosing strains for recipes on purpose rather than by habit. The next step is a split dry hop comparison, which uses the same method on hops.
The harder skill is describing what you taste precisely enough to act on it. That is a trained skill, not a talent.
Your first step: buy two contrasting yeast strains, borrow or buy a second fermenter and plan your next brew as a split.
Common questions
Can I split one batch of wort into two fermenters?
Yes. Chill the wort, split it evenly by volume into two sanitised fermenters and aerate each the same way before pitching.
How much dry yeast should I pitch into 10 litres?
About half of an 11.5 g sachet for wort of ordinary strength. Weigh it on a kitchen scale so both halves get the same amount.
Which two yeasts show the biggest difference?
A clean American ale yeast against a German wheat beer yeast gives the most obvious contrast, with banana and clove from the wheat strain.
