Yeast starters – the hows and the whys
Yeast cells are the often-unsung heroes of beer brewing. Without yeast, your beer would be nothing more than sweet, hoppy water. Those tiny little cells - all 100 billion or so of ‘em - are what give your brew its fruity notes, its spicy notes, its fizz, and its alcohol content.
Any homebrew kit will include a sachet of dried yeast. But making a yeast starter from liquid yeast will usually give you a much better fermentation because you can control the yeast content – and you don’t have to rely on the age or quality of the kit yeast. Making a starter is also an excellent way to make sure your yeast is in fact viable before you put it into a 23-litre batch.
First things: what is a yeast starter?
A yeast starter is basically a small batch of wort - just one or two litres - that gives your yeast a kickstart. When you buy yeast, liquid yeast is dormant, dry yeast is in biostasis (also known as cryostasis), hence liquid yeast is delicate and dry yeast is bullet proof. Making a starter gives liquid yeast a chance to wake up and start reproducing so there are plenty of cells to ferment your brew when you pitch the yeast.
The size of your starter will vary, depending on the brew you make. Fortunately, there’s a very good calculator that does the maths for you.
When to make a yeast starter
You won’t always need to make a starter. Brews made using dry yeast won’t need one - just rehydrate according to the instructions. But if your liquid yeast is old, if you’re pitching lager yeast below 18 degrees, or if you just want to get things moving faster, make a starter. You’ll also want to make a starter for your homebrew if the original gravity is over 1.060.
How to get started with your starter
Plan ahead. You’ll want to give your starter a couple of days to get going before brew day.
A pot and lid
A glass container
A bung and airlock or foil
Before you start, make sure all your equipment is clean and sanitised.
To make a basic starter, mix together water and dried malt extract - about 100g per litre, aiming for around 1.040 gravity. Gently boil for about 10 minutes to sterilise it. Cover and cool it quickly in cold water to room temperature. Carefully pour this into a sterile glass container of your choice - you’ll need one that’s big enough for the yeast to expand and develop some head. A two-litre one is usually a safe bet.
Now’s the time to open your vial of yeast and pitch it. Give the container a bit of a shake to aerate it, and then fit the bung and airlock or loosly cover the top with foil.
While your starter is growing, give it a shake every few hours to get some oxygen into it and to mix it up. Very soon you’ll see it start to get bubbly as the yeast cells become active. And when it’s ready to be put in your brew it should have vastly increased in the number of yeast cells and have a really good head on it.
You can simply pour the yeast starter into your beer when you're ready to pitch the yeast into your brew. In some cases, using a large starter for example, you may want to decant the liquid leaving the yeast sediment to use in your beer. Cooling the starter will encourage the yeast to settle to the bottom before doing this. A general rule is that if the starter is larger than 5% of the size of your brew then you'd be best decanting before pitching.