Why Make A Yeast Starter?
Making a yeast starter is a smart and money saving way to ensure fermentations achieve a desired result. A yeast starter is simply a small batch of overpitched beer made with the intention of propagating healthy yeast cells. This can be done to propagate yeast from a previous batch you made, from packaged yeast, or harvested yeast from a bottle conditioned beer.
Growing Yeast For An Optimal Fermentation
Most packs of liquid yeast for home brewing use have roughly 100 billion yeast cells – some more, some less. Dry yeast’s cell count tends to vary more and has a more limited variety of yeast strains. If you check the yeast manufacturer’s website, they’ll likely have information regarding cell count. With older yeast or yeast kept at an incorrect temperature, a smaller proportion of cells will be viable. However, even with expired yeast or yeast that has been stored out of their recommended temperature range, there are usually at least some live cells remaining.
Use the Yeast Pitch Rate Calculator to determine how many yeast cells you will need to pitch. Then gather the equipment and ingredients to make a starter between 1.035 and 1.045 OG. A lower OG won’t be as productive, and a high OG may stress-out the yeast. Most people use Dried Malt Extract (DME) as with the step-by-step instructions below, but you can make an all grain starter if you wish.
Assuming the DME you are using has an extract yield of 44 PPG, then you need 110g of DME for every 1 litre of water to make a 1.040 OG starter. In US units, this would equate to approximately 3.7 ounces of DME for every 1 quart of water.
Every litre or quart of yeast starter will approximately double 100 billion cells. So, if you’re starting out with three packages of yeast with an assumed 100 billion cells in each, making a 3 litre starter (using 330g DME) will leave you with 600 billion cells. You can make larger or smaller starters for the same number of starting yeast cells, but doubling is the most efficient use of material. If you still don’t have enough yeast cells after doubling once, you can repeat the process.
The size of the container your yeast starter propagates in should error on the large side to aid in aeration. Many people use an Erlenmeyer Flask made of Pyrex as you can both boil and propagate in the same vessel. If you use this, use at least a 2 litre flask for a 1 litre starter otherwise you will get a boil-over. Another option is to use the vessel you’re going to ferment your beer in to also propagate the starter.
Aeration and agitation are also important with a yeast starter for maximum healthy yeast growth. Be sure to aerate (or oxygenate) sufficiently using with whatever method you are familiar. It is also common to use a stir plate as well, but this is entirely optional. A stir plate has a magnet you put in your propagation vessel that acts as a stirrer which utilizes magnetism from the plate below for continuous stirring.
Ingredients And Equipment Needed For A Yeast Starter
- Yeast Nutrient (optional)
- Heat source (i.e. a stove/hob)
- A pan for boiling if you’re not using an Erlenmeyer Flask
- A funnel
- Aluminum foil or a loose fitting airlock
- A container for propagation (clear is better because you can monitor activity)
- Ice (and a sink to put it in) or a chilling coil
- A Thermometer
- A stir plate (optional)
- Sanitize everything that will come into contact with post-boil wort
- Bring water to a boil
- Add DME while stirring as to avoid scorching (note that DME is quite sticky)
- Boil for 10-15 minutes and WATCH FOR BOIL-OVERS!
- Make an ice bath for post boil
- Add yeast nutrient towards the end of the boil (optional)
- Chill in ice bath
- Transfer to your propagation vessel (if you didn’t boil in it)
- Aerate once the temperature is in the range of 20-24oC (68-75oF)
- Place stir plate stirrer in propagation vessel (optional)
- Pitch starting yeast
- Cover propagation vessel loosely
- Keep around 20-24oC (68-75oF). See considerations below.
- Shake or stir for further aeration every so often for the first 12 hours (optional if not using stir plate). The wort should have a milky appearance due to the active yeast. It may or may not develop a Krausen.
- Pitch, store, or make another starter. Here are your options:
- Pitch the entire starter at High Krausen (i.e. peak activity). See considerations below.
- After there is no visible activity (roughly two days), refrigerate for a day to let the yeast settle and decant the excess liquid. The yeast will be the light color top part of the sediment, so don’t pour this off. From this point you can either:
- Pitch the yeast after giving it a good swirl.
- Make another starter and repeat the above instructions if you need more yeast cells.
- Store the yeast for up to a few weeks refrigerated provided you have good sanitation. If you want to store them longer, you should make another starter before using them.
Water – The water you use for your starter does not have to be the same profile as for the beer you’re going to brew, with a possible exception being pitching at High Krausen. You should ensure though that the water used for your starter has the minimum mineral content for yeast health. So in other words, don’t use untreated RO water.
Yeast Strain – If you’re using a strain of yeast (such as lager yeast) that’s optimal temperature range is below 20-24oC (68-75oF), you should still propagate your starter at 20-24oC (68-75oF) with a possible exception being pitching at High Krausen.
Pitching at High Krausen – If you are planning to pitch your yeast starter at High Krausen, you may want to have a similar wort composition for your starter as the beer with which you will be pitching it. The reason being is that the active yeast cells at High Krausen have been acclimated to living in one environment, so a drastic change of environment should be avoided. Additionally, you may want to propagate your starter within the yeasts recommended temperature range and using a similar water profile to avoid off flavors. This is most applicable if what you will be brewing is a “cleaner” styles of beer such as light lagers. Keep in mind that lower temperatures mean a longer time.