Why make yeast starters?
The quantity of yeast in a Wyeast "smack pack" typically isn't anywhere near enough to give you a fast, healthy fermentation. That's why it is a good idea to make a starter. The idea behind making a yeast starter is to provide the small number of yeast cells from a Wyeast package with an ideal environment in which they can build up their health and numbers, with no competition from other competing microbes. Then, when the contents of the starter are pitched into your wort, you will get a shorter lag time, and a faster fermentation. This in turn will result in a cleaner tasting beer, and reduce the chances of infection, because your yeast will take over quickly, leaving little time for unwanted microbes to gain a foothold.
Even the "pitchable" liquid yeasts (e.g. Wyeast XL packs, and White Labs vials) will benefit from a starter, especially if the yeast is more than a couple of months old, or will be pitched into a high gravity (> 1.070 OG) wort.
The following steps illustrate how I make yeast starters. This certainly isn't the only way to make starters; but it has worked very well for me. I call this my "Zero Transfer" starter procedure, because the starter wort is boiled, cooled, pitched, and fermented in the same container. The lack of wort transfers results in the closest you'll get to a sterile environment, short of resorting to fancy lab equipment. Since I switched to this procedure a couple of years ago, I have not had a single infected starter (knock on wood).
Required materials & equipment:
1. The first thing you want to do is get your 20 oz. of water good and hot, then add it to your DME. Stir until the DME is completely dissolved.
2. Pour the wort into the flask (a small funnel is helpful here). Crimp a double thickness of alumimum foil over the mouth of the flask, and put the flask on the stove, over medium heat. Bring the wort to a boil, and boil for about 10 minutes. Watch out for boilovers; in particular, don't be tempted to turn the heat up to high to get it to boil faster -- this is a sure-fire recipe for an explosive boilover, which will result in sticky, burnt wort all over your stove burner.
3. Remove the flask from the heat. Be careful, and use a potholder or dish towel to pick up the flask -- it is very hot. The surface of the flask -- even near the top -- can reach temperatures in excess of 200°F (93°C)! This is what we want, because it will sanitize the entire interior of the flask. Cool the flask in a cold tap water bath, changing the water whenever it gets warm. As the wort cools down, ice can also be added to the water to speed things up, if you like. If your tap water is warmer than about 65°F (18°C), you will need to use ice to get things cooled down in a reasonable amount of time. Swirling the flask will also help.
4. When the flask is cool to the touch -- 60-70°F (16-21°C) -- remove it from the cold water bath. Then, holding your hand over the foil to keep it in place, shake vigorously to aerate the starter wort, until the headspace is full of foam.
5. Sanitize the outside of your Wyeast pack, shake well, cut it open (make sure the scissors are sanitized too!), and add the contents to the flask.
6. Put a sanitized rubber stopper and airlock on the flask. I recommend boiling the stopper to sanitize it; but don't boil the airlock unless you know it is made of plastic that won't melt! Add enough weak sanitizing solution to the airlock to cover the bottom of the float.
Now put the finished yeast starter somwhere that the temperature will stay at about 70°F (21°C). You can either allow the starter to completely ferment out (usually 2-3 days), decant most of the liquid, and pitch just the slurry; or you can pitch the entire starter into your batch of beer, while it is actively fermenting (typically after a day or so). Both approaches have their advantages. Letting the starter ferment out and decanting means you're not adding a lot of "foreign" wort to your batch of beer. But pitching while it is active will result in a shorter lag time.
Make sure you sanitize the mouth of the flask, before attempting to decant the starter wort, or pour out the yeast slurry. I use a sponge dampened with Iodophor sanitizing solution.
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(Posted to Web October 8, 1999; last updated March 13, 2000)