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How to make a Yeast Starter
One of the best ways that you can dramatically improve the taste of your homebrew is by pitching the proper amount of yeast - and that means in a lot of cases by making a yeast starter. It's very easy and only requires a small bit of equipment and extra time. Having the proper amount of yeast also means a shorter lag time in fermentation and less chance for infection.
Some homebrewers swear by dry yeast, but there are beer styles such as Kolsch and most Belgian styles where you simply can't use dry yeast and achieve the proper results. In these cases you will need to use a liquid yeast strain - and in most cases you should make a yeast starter. Liquid yeast strains for homebrewing are widely available from two companies - Wyeast and White Labs. Wyeast packages their liquid yeast in what are called "smack packs" - which are foil pouches that contain not only the liquid yeast, but an activator pouch, that when ruptured release yeast nutrients that jumpstart yeast production. White Labs yeast comes in plastic vials that contain a bit of the yeast strain in a slurry. Both companies claim that the contents of their packages contain enough active yeast cells to ferment a five gallon batch of beer, but it is not advisable to do so unless your beer is a lower gravity beer (1.050 or lower).
This is where you need a yeast starter. A yeast starter is basically just a way of growing your yeast population to the level it needs to be at to ferment whatever beer you are making. You will definitely need a yeast starter when you make high-gravity beers and lagers. The idea is to use dried malt extract to make a small amount of low-gravity wort and then add your yeast and maybe a bit of yeast nutrient. The yeast will reproduce and over the course of about 24 hours increase the number of yeast cells to the proper number needed for your beer. You can also do this in stages to dramatically increase the number of yeast cells if you are making a very high-gravity beer.
Equipment/ingredients you will need:
Dried malt extract
glass vessel or flask
sauce pan or stock pot (capable of boiling a liter or two of wort) with lid
Yeast packet or vial
Airlock or foil
Sanitizer
Optional equipment/ingredients:
Yeast nutrient
Stir plate
Make sure that you sanitize everything that will come in contact with the yeast starter.
You'll want to make your starter 2-3 days before your brew day. If you are stepping your starter up to a larger size, then plan on making your starter 5-7 days prior to your brew day.
To make your 1 liter starter wort, you are going to dissolve 100 (approx. 3.5 ounces) grams of dried malt extract in 1 liter of water in a sauce pan on the stove. If you have a gas stove, you can do this right in your glass flask (if it is a borosilicate glass such as Pyrex) - just watch out for messy boilovers and always use a pot holder for handling hot glass. There are also products such as Fermcap that will help prevent boil-overs. If you are using yeast nutrient, add it to the wort before you bring it to a boil.
Bring the wort to a boil for 20 mins. Then move your flask or sauce pan to the sink and cool using an ice bath. Cool to below 70F. If you used a sauce pan, then cool the wort while its in the sauce pan and then pour the cooled wort from the sauce pan to the flask. Make sure that the flask has been sanitized and anything else that will come in contact with the cooled wort, such as your funnel. Also sanitize the outside of your yeast packet/vial. Once your wort has been chilled to below 70F and it is in your glass container/flask, it's time to add your yeast. Make sure and swirl around the yeast so you can get as much yeast in your starter as possible. After your yeast has been added, swirl the mixture (or shake it if you can) to feed your yeast the oxygen they need to reproduce. Put your sanitized aluminum foil or airlock on your glass container/flask and you're done!
If you have a stir plate, add your chilled wort and yeast to the flask, then put your sanitized stir bar in the bottom of your flask and put it on top of the stir plate and turn it on. You can purchase a stir plate from your local homebrew store, online, or make one yourself using parts from an old computer and some odds and ends from your local Radio Shack. A stir plate keeps your yeast in suspension and is continuously feeding it oxygen. It will dramatically increase your yeast cell count compared to just giving it an occasional shake/swirl.
After 24 hours, you should see a good bit of yeast in the bottom of your starter. Move the starter to the refrigerator and let it sit another 24 hours. This will make all the yeast settle to the bottom of your flask. If it is enough yeast for the beer you are making, simply pour off the liquid on top of the starter let it come to fermentation temperature and pitch the yeast slurry into your wort when you are ready.
If you want to increase your yeast count even more, you can step your starter up. If you want to step up, then you are going to want to make another starter wort, this time double the size of the original starter. So, if you started out with a 1 liter starter, make a 2 liter starter next. If you started off with a 2 liter yeast starter, then make a 4 liter starter next. Use the same procedure as you did for the original starter, but add the yeast slurry from your original container (make sure and decant the liquid above the yeast before you step up to the next size). You will need to use larger containers for each step, unless you go ahead and use a large container to begin with. Beer growlers are great for 1/2 gallon starters and clear wine jugs work great for 1 gallon starters. This is a great way to grow a lot of yeast and it only takes a few days. It is very important that you give your starter plenty of time in the refrigerator so the yeast can settle to the bottom of your container/flask. If you don't wait long enough, you can pour off some of the best yeast in your starter. So be patient and you will be rewarded with some healthy, strong yeast. Happy brewing!