Stir Plate Construction

by Hank Bienert

At a recent meeting I heard sad tales and anxious reports about 3 day lag and the cost in time and treasure of needing to buy new yeast for sequential brews of same style. NONE of this anguish is necessary. I am a dedicated ‘yeast rancher’ having read about and then validated how robust yeast are in the second to fifth generations.

The stir plate will make plenty of strong yeast even from 2 yr past “best date” original liquid container or stored in frig harvested 7 months ago. Dry yeast stored in frig loses about 4% viability/year so will last a long time BUT if aerated give a better start … MORE CELLS WIN OUT!!

How to have the strongest yeast possible and then have it again
2b Build a Basic Stirplate for Yeast Suspension
Using a stirplate keeps the yeast in your starter not only constantly suspended, but provides constant aeration as well.

• 1 box (size nearly unlimited)
• 1 computer fan 12v
• 1 dc power supply 6v
• 1 rare earth magnet
• 1 rheostat (pot) 25 ohm 3watt
1 power toggle switch (optional)

Nearly any wood or plastic box large enough to hold a muffin fan will work. HD/Lowe’s/Amazon sell small project boxes cheaply. Cigar boxes or smaller wine boxes would work as well (Hank used an inverted old Tupperware bowl at least 3” deep-the lids warp in the dishwasher so there are a lot of naked bowls available) Use your imagination, even the cheapest of pine boxes look great with cherry stain and a few coats of polyurethane. I’ve even seen a post where a guy built one into a plastic tool box, which conveniently held other small brew gadgets on the inside. Computer fans are cheap.
…read: FREE. We like things that are free since they are so reasonably priced!)

Failing computers are a great source of fans, either in the power supply or case. If not, these fans are available at any computer parts store for $5 to $10. Get a 12v fan that is roughly 4” x 4”. DC power supplies are usually abundant. Anyone who has gone through several cell phones, digital cameras, and other small electronics probably has a drawer somewhere full of unused power supplies, so ask around (again read: FREE). Otherwise, your friendly neighborhood electric department or online supplier should have them for a few dollars. A 6v DC power supply is what you’re after, though a 9v or 12v would work with fiddling. Rare earth magnets can be harvested from dead computer hard drives. All you need to do is open the hard drive case and remove the magnet from the read/write head (again, read: FREE). I’ve gotten a lot questions about just how to get these magnets out of the hard drive, Rheostats can be found at electronic shops, at electronic stores, or online.

Rheostat Tip
The computer fan spins so fast that you really only need 10-20% of its power. Spinning much faster than that will spin the magnets so fast that excessive turbulence is created inside the flask (suspending the yeast is one thing, making them pull 5 G’s is another). The 25 ohm pot provides enough resistance to get the fan spinning at its fastest potential, with its minimum speed being just about right for yeast suspension. The combination of 12v fan and 25 ohm rheostat seems to be a good one for both 1 liter and 2 liter flasks, though nearly any combination could work with some tweaking. If a 9v or 12v power adapter is used, you can employ a fixed resistor or second rheostat to add resistance and slow the fan down. This is the fine control which is mounted to the box wall with the control knob on the outside.

I don’t think I can describe the wiring in way that would be detailed enough to be helpful. So the following is a very general description. Splice your fan’s power cable and connect it to the cable of the 6v DC power supply. I soldered my connection and covered with shrink wrap, but wire nuts and/or electrical tape would probably suffice. The toggle switch and pots will also need to connect into the power line (if you use two pots, just put a short jumper cable between the pots for power and ground). Setting all the components in place and making your best guess would work fine. If the system doesn’t work, switch something around. If you’re handy with an ohmmeter, you can save yourself some time. Or like me, find someone who is skilled in this area and promise them some homebrew if they lend a hand.

In the past, I followed the advice of Jamil Zainasheff from Mr Malty. Jamil gives an incredibly informed and detailed explanation of yeast, starters, and pitching on his site but this is TMI and not really needed. I make a batch of wort two days before my brew day and cover with plain old foil. After the wort has cooled, yeast is pitched and aerated (I use an O2 stone) I put the flask on the stirplate and spin for 18 hours. Generally speaking, a properly prepared starter can increase yeast cell counts from 100 billion to 240 billion in two days.

Then to make sure I haven’t been just shuffling around dead cells, I pour some into a bottle, add some fresh starter and put on a bubbler. If it works you will know. I always have a pack of 34/70 or SAF 05 as back up BUT have never had to use them as emergency BUT used them (after stir plate tickle) after a decade Harvesting yeast and fermenting I got rid of dangerous glass fermenters years ago and use 7 gallon bucket which I visit every 12 hours post pitch until krausen begins then every 24 hours. Pitching is accompanied by vigorous stir with electric whisk x 2 minutes which gives SAME O2 SATURATION AS O2 TANK BLAST SINCE O2 IS IN ATMOSPHERE plus it mixes yeast into entire wort and easier to setup and acquire.

When initial krausen appears I scrape off grungy protein/hop residue and next day or when ever a beige to white later WITHOUT particles, I take 90% into a sterilized small jar and repeat next day into ANOTHER small jar.

Trub harvesting is also good IF you have cleaned grunge off but if not then,why harvest sour protein/hop residue and add to to next batch? The day before I plan to transfer from the primary, I microwave 3 8oz mason style jars 3/4 full. After FULL boil x 8 mins I remove carefully, pour a bit from each jar onto its inverted top so very hot water also washes lid bottom. With tongs, place loose fitted caps on each up and LOOSELY tighten caps and when cooled down, place in frig.

NOTE The standard brewing book recipe is too small so I always boil for 6 gallon result and I reserve the so-so dregs, not the thick dregs, refrigerate it X 24 hours to drop out the thick material and freeze rest as a starter – a Hank Wortcicle). This allows me to ferment 5.5 and serve about 5.

Day of transfer I siphon until some cloudy material starts up tube then stop. We want GOOD beer not lots of poor beer. I discard undesired material leaving a light cover of liquid. Add the contents of each of ONLY TWO jars and QUICKLY replace but don’t tighten caps and swirl trub around then decant to within 1/2 inch capacity then loosely cap. If enough material repeat into second jar. DO NOT ADD CHUNKY OR DARKER THAN BEIGE trub.

I have tried Agar plates and Agar or nutrient slants applied by professional lab tech friends and this harvesting is easier with excellent results. I date jar and always smell and taste a sample before spinning. I do NOT use if older than 12 months or 5th generation or high alcohol and refuse to store/reuse Belgians more than 2 months – Those Belgian yeasties are crazy already and I suspect long confinement followed by spinning will throw them over the edge!!

WHAT ABOUT UNUSED THIRD JAR? In case I dropped or contaminated other ones :>)

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