Andy and I have been yammering on a bit about yeast this week, since it is Yeast Week here at RealHomebrew.com. Some companies have Shark Week. We have Yeast Week. It's just as frightful and exciting, though on a microscopic level. One issue we have mentioned but never delved into is that of yeast starters. A yeast starter is like a mini-batch of weak beer designed to let your yeast grow and multiply before you add it to the wort. This increases the potential efficiency of the yeast.
One thing many people seem to agree on is that if you use dry yeast, you do not need to use a starter. Most commercially available dry yeasts have about 200-250 billion cells already, and will have instructions on how to rehydrate the yeast and at what temperature to pitch and ferment it. To put this in perspective, a normal five-gallon batch of beer needs something on the order of 180-200 billion yeast cells to properly ferment. If you like using liquid yeasts, however, you definitely should use a starter of some sort. Both White Labs and Wyeast have about 100 billion yeast cells in their products, so they are great candidates to make starters with. If you look merely at the price of yeasts, you may be wondering why you should go for a liquid variety at all. The dry yeast packs have more cells, are cheaper, and require less handling. Why go with liquid? The answer is easy. You have more variety in liquid yeast than you do with dry styles, so sometimes it makes sense to go with liquid.
When you get your yeast home and are ready to make a starter, you have a couple different ways to proceed. You can either use a stir plate, which will be more efficient, or go without and just take a more hands-on approach. A stir plate constantly stirs your yeast slurry and draws oxygen into the mixture by creating a vortex, as in the photo above. I bought my stir plate for $45 but they are easy to make as well, if you are more industrious than lazy, which I am apparently not.
If you don't use a stir plate, you have to swish the starter around in the bottle several times a day to mix it and draw oxygen into the wort. It's not a big deal, just requires some extra maintenance.
Plan on allowing your starter to sit and grow for about 48 hours before you use it. I made my last starter on a Saturday and brewed on a Monday. That is about the right amount of time to let it do its thing.
Getting Started
First, remove your yeast from the refrigerator and let it sit out for a couple hours so it can slowly warm up to the ambient temperature. If you are using a Wyeast smack pack, follow the normal process of smacking it and letting it get all big and bulgy before beginning to make your starter.
Most beers can use a one-liter starter but bigger beers, like barley wines, may need more yeast growth and deserve at least a two-liter starter. Make a 10:1 ratio of water to light dry malt extract (DME). Heat this to boiling and cook it for 10-15 minutes. Cover the pot and put it in an ice bath in the sink to cool it to room temperature. Pour it into a sanitized Erlenmeyer flask or empty bottle and add your yeast. If you are using a stir plate, put in the sanitized stir bar at this point.
Cover the mouth of the flask or bottle with sanitized aluminum foil, allowing some room for air to get in and out. As the yeast grows, it will need some new oxygen to come in. Loose aluminum foil is a good option because it can let a little gas exchange but will be enough of a mechanical barrier to keep harmful bacteria out. Whatever you do, do not use an air lock. That will only allow the carbon dioxide to escape and will not let any new oxygen in.
Put the flask on the stir plate and adjust the speed so that you get a slight vortex. If you are not using a plate, simply swish it around the jar for about a minute. Do this a few times per day.
The night before you brew, put the yeast starter slurry in the refrigerator overnight. This will allow the yeast to settle to the bottom of the container so you can gently pour off the beer the top. Let it come back to room temperature, mix it up again, and pour it in your wort when you are ready. Be careful pouring out your starter, though, because it is easy to lose the stir bar in your fermenter.
Making a yeast starter is easy and can definitely help you get a more thorough fermentation.