A yeast starter is a solution that enables yeast cells to propagate (or reproduce). It resembles a mini-batch of beer but is not meant for drinking. Instead, you add it to your wort to ferment a better final beer.
Why Make A Yeast Starter?
The fewer yeast cells available for fermentation, the more likely you are to end up with stressed yeast. Stressed yeast, like stressed human beings, is the result of too few cells assigned to too much work. Your beer will ferment, but it will be of lower quality.
Conversely, more cells equal better fermentation. Yeast starters increase attenuation or the efficiency with which yeast ferments the sugar in your wort.
How Does A Yeast Starter Work?
The secret to a yeast starter is aerobic respiration or keeping oxygen in the starter so that the yeast ferments very little, mostly just increases in cell count. For mail-order customers, yeast starters also have the advantage of "proofing" the viability of yeast before brew day.
You will make a "mini wort" by boiling dried malt extract with water, cool it, put it in a flask, and pitch your yeast into it. A foam stopper will provide some protection from infection, but still allow oxygen into the starter for adequate aeration. Best results can be achieved by using a stir plate, which will keep the yeast in suspension and increase activity, and your yeast will be ready in less time.
If you are unable to use a stir plate, giving the flask a good swirl from time to time is advisable. It will also give you a good indication that the starter is going since CO2 bubbles will come out of solution as you swirl it around, provided your yeast starter is in good health.
24-48 hours is usually sufficient time for yeast starters (although some strains like lager stains can take a bit longer to propagate). It is best to pitch the yeast at or just after peak activity, when your cell count has increased substantially, but while the yeast is still active. This will ensure a healthy fermentation in your beer and decrease the lag time before fermentation begins. Click here for a Printable Yeast Starter PDF.
How To Make A Yeast Starter
Yeast starters are easy! You just:
- Boil a small amount of water and malt extract
- Cool the mixture down
- Combine with the liquid yeast in a small vessel with an airlock or foam stopper.
If you cannot make a yeast starter, you can pitch additional packs of yeast, but this is not as effective as making a starter.
If you're brewing a big beer, we highly recommend making a yeast starter 24-48 hours before your brew day. An average pack of beer yeast is designed to ferment an average strength ale, usually about 1.040 starting gravity. Fermenting a beer up to about 1.060 in gravity is no problem for a single yeast pack, but a gravity higher than this presents some special challenges to the brewer. You can easily imagine that a beer with twice as much sugar to ferment is going to need at least twice as many yeast cells. It also helps a lot if the yeast cells are healthy and active instead of dormant.
If you don’t make a starter for a strong beer, the yeast will likely not be able to handle the high amount of sugars and will leave the beer sweet and uncarbonated. Making a yeast starter dramatically increases your yeast cell count and also gets the yeast active and ready to ferment. Lager fermentation also greatly benefits from the use of a yeast starter, as the higher cell count will reduce the lag time before fermentation begins and help prevent off-flavors.
Read More About Yeast:
Yeast for Brewing Beer - So what is brewing yeast anyway?
Yeast Nutrients and Yeast Energizers - Keep your yeast healthy.
Dry Yeast and Liquid Yeast - Check out the pros and cons.
Hydrating Dry Yeast - Is pitching dry yeast directly the best method?
5 Easy Tricks For Boosting Yeast Health