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> Stir Plates 101, from the Northern Brewer Forums
cj in j
post Apr 9 2005, 06:11 PM
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Stir Plate FAQ
contributed by johnm42, Beershasta and Beth
This FAQ was originally posted in the Northern Brewer FAQs Forum, used with permission.

Q. How much would I spend for a stir plate?
A. For under $30, you can build your own stir plate. For anywhere from $30 to $100, you can find many good used and some new stir plates.

Q.Will it help my brewing?
A. Most definitely. The stir plate will keep your yeast constantly suspended. This will benefit the yeast in several ways. First, in the early stages, it will help provide the wort and yeast with extra oxygen, especially if you leave the container loosely covered and/or bubble filtered air through it. Second, once the yeast starts fermenting the starter wort, the stirring action will knock the CO2 out of solution, leading to healthier yeast. And third, the yeast will stay in contact with the sugars in the wort for a longer time. The result of all this is that the yeast will produce more and healthier cells, which will reduce, lag times and ferment further and faster.

Q.How do I use a stir plate?
A. Just follow these easy steps:
1.Place a magnetic capsule in the starter before boiling. The 1-inch capsule is fine for a 1L flask while the 2-inch works well for most anything else that finds its way to the stir plate. The 3-inch is a little large and tends to be "thrown" out of the center fairly easily.
2. Check that the motor is off. Tilt the container so the capsule goes to the lowest part, carefully return the container to horizontal, set what was the lowest part on the center of the stir plate and slide the container to the center of the plate. Usually, you'll hear the capsule sliding.
3. Turn on the plate at low speed until the liquid is obviously rotating. If you hear the motor turning but don't hear the capsule turning, repeat step 2. If you hear the capsule turning but don't see motion, turn up the speed a little.
4. When you see motion, slowly in steps increase the speed until you have a fairly wild vortex. Leave it for 10 minutes so the wort can absorb O2. It will do so quite efficiently. If you should "throw" the capsule by turning it too high, start over at step 2.
5. After aerating the wort, pitch the yeast and reduce the speed so there is a nice vortex. Leave a cover on the container loosely for good gas exchange. A sanitized piece of aluminum foil, folded over once or twice to give it extra strength, works fine as a cover.

Q.How long does it take to complete the starter?
A. Most starters will finish in 24 hours. Even a 4L starter takes only 24 hours. Generally, you can tell when the starter has finished by watching the speed of the swirling. Early in the process, the wort will be swirling quite quickly. Once the yeast starts fermenting, the swirling will slow down and the wort will appear muddy and thick. When the yeast is finished, the swirling action will speed up again. That's when it's done.

Q.What do I do then?
A. Pitch the yeast right away, if you are ready for it, or put it in the fridge and let the yeast settle out overnight. You can keep the starter for at least a week or two. Pour off most of the spent wort, stir the yeast cake into the small amount left and pitch the yeast slurry.

Q.Are there any more handy tips about Stir Plates?
A. Why, yes!
1. You can also use O2 if you use it to oxygenate in your flask during that initial aeration period. I do this. I place my O2 line in the flask and run a measured amount while the "wild" vortex is active. [See stout_fan's thread on Air Injection with a Stir Plate for another option.]
2. You can build up starters for lagers by following the instructions once and then placing the starter in a refrigerator. The next day, make another starter, decant the top fluid off your previous starter and pitch the new starter "fuel" on top and re-follow the same steps. This way you basically have a cell count that is double the standard amount of the normal one.
3. At pitching, you can use a magnet and pull the stir bar to the side of the inside of the flask. This way when you pitch, your stir bar won't fall into your wort. You can also note that an extra stir bar is useful incase one goes into your wort. This would make your stir plate useless until your beer is finished fermenting.
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