Thursday, November 15, 2007

Magnetic Stir Plate


This is one of the better brewing investments I've made in the last year. The magnetic stir plate is very good at kick-starting the beer yeast. I typically create 2 liter yeast starters from a single pack of liquid yeast.

I have three erlenmeyer flasks, in 1 liter, 3 liter and 5 liter sizes. The 3 liter one can be seen in the photo above.

Creating the yeast starter is straightforward: Fill the flask with water from the tap. Put it on the stove, turn on the heat and wait until the water heats up. Then add 1 tablespoon of dried malt extract per dl of water. Then add 1/2 teaspoon of yeast nutrient. Stir well and let it boil for about five minutes in the erlenmeyer flasks. This makes sure that both the yeast starter and the flask is properly disinfected. Cover the opening of the flask with aluminum foil or plastic wrap to prevent things from falling into the pristine wort. Cool it down to about 20 degrees C in a cold water bath before adding the yeast. Then spray the scissors and the opening of the yeast pack with a strong alcohol solution to make sure that no bacteria gets in contact with the yeast on its way to the yeast starter. Wait for the alcohol to evaporate before opening and pouring the yeast into the erlenmeyer flask. Finally, add the stir bar (make sure that it is disinfected) and put it on the magnetic stirrer. The stirring will provide the yeast with lots of oxygen.

It usually take a day or two before the yeast has fermented out the yeast starter.

15 comments:

Adam said...

I was thinking of buying one of these. Can't justify the cost yet though. I suppose 17 or so batches of beer made with propagated yeast would be enough to pay for it.

grove said...

I definitely recommend getting one. :)

Travis said...

I was reading about these in BYO. It's pretty interesting stuff. How much of an impact do you figure it will have (from a practical sense) on the end product?

Adam said...

From what I can tell it helps you get things done more quickly. So if you have an old yeast that takes a while to start (like my WLP002 I just used) it could save you a day or two.

Are there other advantages?

grove said...

The magnetic stirrer will produce more healthy yeast cells. It will also keep the yeast in suspension at all times making sure that there are no dead spots and makes for each contact with the wort sugars. The stirring increases oxygen levels and will drive off the CO2 (which suppresses yeast activity).

Adam said...

Thanks Grove :-)

Matthew said...

Where did you get the stirrer? I've been thinking about getting one, but found none in Norway, so now I will just build one from an old pc fan and harddisk.

grove said...

matthew,

I got it from VWR via a friend of a friend. :)

It looks like you should be able to order it directly from them through their web site.

New Homebrewer said...

I'm not trying to be a smart ass I'm very new to brewing but Why not just use a blender or similar device? Wouldn't that be cheaper?

matdm said...

I've built a stirrer and it works wonders. You really get a lot of yeast for a relatively small amount of wort. I've been using just 1L starters and have been getting short lag times even for lagers, though of course a 2L starter won't do any harm, just as soon as I get some larger erlenmeyers.

I don't think you can achieve the same effect using a blender. It will probably spin too fast, will be hard to sanitize effectively, and will certainly be noisy, if it's anything like the blender I have! I can't bear to hear our blender for more than a few minutes, let alone 2-3 days!

Olek said...

Why don't you just add the magnet directly to the flask before boil-up. Less sanitizing to do. The stir bar is teflon coated and can definetly take the heat.

grove said...

Olek,

Yes I agree. Adding the stir bar to the flask before heating sanitizes it. But don't add it while it is boiling as this will cause it to boil over. Trust me on that, as I've tried it. :)

Olek said...

Ah.. Didn't think of that, and I'll take your word for it. :)

Regarding the link to VWR; I dont think they sell to "regular people". At least what they told me last time I met with them (via work). Registering as a company would do the trick they said, but it might be he was mistaken...

Ryan said...

I built one from a 12V DC computer fan and some rare-earth magnets. Including a flask and stir bars, it cost me about $50.00 all up. Breaking it in right now with a Belgian Tripel!

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