Stir plate and starter woes

[Painter]

I have been wanting to get into making starters, especially after having some problems with stuck fermentations. Because I'm kind of cheap and I like to build things I made my own stir plate, though I didn't have an old computer to scrounge form, but a new computer fan and other components cost about a quarter of what a store bought stir plate would.

So the big problem that I have been having is getting the stir bar to rotate. The magnets are strong enough that they hold the stir bar to the bottom of the flask if I just turn it on. I have found that by picking the flask up and swirling it a bit I can sometimes get the stir bar spinning, but it is really hit or miss and with the cloudiness of the wort in the flask it is difficult to tell whether it worked. Then it is also possible to throw the stir bar if the rpms are cranked up too fast. Any suggestions.

Now I have a flask of starter that I started about 14 hours ago. It is fermenting, but it went many hours without the stir bar turning. Also, the temp in the kitchen last night got down to the mid to low sixties. I will have to remember to use a small blanket or something to insulate the flask next time.

I was planning on brewing later today, but I'm not at all certain that the starter is or will be ready to use. Any way of telling? I'm tempted to put of brewing until tomorrow and start a new starter this evening. Again, any suggestions?

 

[LLBeanJ]

Any starter is better than no starter. Keep swirling it whenever you think about it and brew today as planned. I'm sure it'll be fine.

 

[Epimetheus]

This works for me, it might work for you. I put the flask and stir bar on the plate without starting it, then plug it in. Powering up from zero with the stir bar in place seems to give the magnets time to grab. I use a computer fan and run it at 4.5V. It think it is 12V so it runs slower.

My room temp is always 65F - 68F, it makes a good 1l starter after 16-24 hours. Any suggestions to improve the process are welcome.

 

[vNmd]

I sometimes have to crank up the RPMs to get the bar moving but then turn them down once it gets started. I think as long as it is moving - they are gold. My temps are in the mid 60's which is perfect for the starters. I want to have the starter temp close to the temp it will be pitched into. I don't want to shock the yeasties when adding them to their new home. Some people don't use stir plates and still get a good starter. It might not be optimal but it is still going to be better than the original cell count.

 

[Queequeg]

The normal problem with sir plates both homemade and commerical is that if the speed is to high the magnetic stirrer bar will be bounced off the magnets. So normally you start low and increase the speed gradually.

Normally on the home built models even if you put in a potentiometer of some kind the fan speed won't rotate slow enough and what happens is the magnetic rotate x2 the speed of the bar meaning that polarity of the magnetics and the bar match cause both poles to be repelled.

However I have never heard of the bar not turning but being pulled to the base. The only way I could think this would happen is either 1) you are using the wrong size bar or 2) the magnets attached to your fan are both the same polarity either side of the pivot. They need to be opposite to get a proper spin, I have seen a few homemade stirrers on the net that work despite this but they drag the bar around as opposed to spin it 3) you stirrer bar must have a float point in the middle to lift it away for the flask base to enable it to spine freely.

 

[Homercidal]

Yes, something is wrong. It's just not really possible that the bar is held down fast and won't turn.

I've made a couple of these from scratch and the worst part is centering the magnets. After that it's a matter of shimming the flask with some rubberized shelf lining to keep the flask from vibrating off (Or to get the 1 gallon tea jug to not hit the magnets since the bottom is slightly rounded.)

I'd focus on double checking the magents.

After that, realize that you don't need a "vortex" to make a starter. Just get it going to keep the yeast suspended and continually coming in contact with the surface. Even a small dimple is plenty.

And if you get totally frustrated, I know Stirstarters make a good product and stand behind them.

 

[william_shakes_beer]

Here's what you do:

1. Get the center of the stir bar aligned with the geometric center of the fan AND the magnetic center of the base magnets.

2. slow the speed of the fan by reducing the voltage from 12V to 3.5 or so

3. Keep the base magnets spaced from the fan motor so they will not lock the fan rotor.

I used 2 hard drive magnets on the base, but any rare earth magnet that is longer than the stir bar will do the trick.

Try this:

1. With a hole saw, cut a wood disk 1/2" thick x the diameter of the fan hub.

2. Away from any metal objects, place the stir bar on the base magnet(s) and then glue the base magnet(s) to the wood disk so the center of the stir bar aligns over the center of the wood disk. Allow glue to dry completely

3. Glue the wood disk to the fan hub so the center of the wood disk sits over the rotating center of the fan. Find a way of restraining the disk until the glue dries. This is important, because the magnet will try to move the wood disk to the magnetic center of the fan. Until dry, the glue asks as a lubricant.

4. The hard part is done. Put your fan in a box, adjust so the magnet is as close as possible to the bottom of the starter vessel as possible without touching it. I made a wood box with a plexiglass top.

5. Find a way of reducing the voltage from 12V to about 3. I got a multi voltage wall wart and end up setting it to 3 volts.

6. Be sure your starter vessel has a thin flat bottom. I use an Eflask.

Test:
Put some water in your vessel, drop in the stir bar. Place the stir bar (now inside the water) over the base magnets till it catches, then move the vessle so the stir bar is in the center of the water. Turn on the power, beginning at the lowest setting and slowly turn up until the bar turns merrilly. I found that 1.5 volts is not enough, but 3 is. YRMV.

Note the lowest voltage at which the stir bar turns, and the voltage at which the stir bar is slung off. That is you min/max setting. If the stir bar is aligned correctly, you can get a full column vertex in a 2 L flask. Neat party trick, but in reality you just make the yeast dizzy. Lowest setting is fine.

 

[Painter]

Thanks everybody.

When I put my stir plate together the first thing that I did before I even tried it for the first time was to check the polarity of the magnets. I assumed that the stir bar had an N pole and an S pole. Then I labeled the magnets that I was going to mount on the motor so that there would be one N pole and one S pole facing up. The 2 inch washer that I used on the motor, as a mounting plate for the magnets, wasn't going to "care" about the polarity of the magnets stuck to it, but I wanted to make sure that there was an S polarity magnet sticking up on one side, and an N polarity magnet sticking up on the other side. That way, the N end of the stir bar would go to the S pole of the magnet on the motor and the S end of the stir bar would go to the N end of the magnet on the motor.

To test it, I put some water in the flask, put the stir bar in, put the flask on the plate and turned the plate on at its lowest rpm.The first time, the stir bar just vibrated, but did not turn. After looking at it for a few seconds...um, well maybe minutes...I concluded that even at the lowest speed that I could run the motor, the magnets were strong enough, and the RPM's fast enough, that the stir bar was being held against the bottom and couldn't gain enough momentum to turn before the motor made another complete revolution. I then lifted the flask off of the stir plate, saw no change, then swirled the flask in the direction of the spinning motor. The bar started to spin. Thus my conclusion that the magnets were holding the bar too tightly against the bottom of the flask. But I admit there are other explanations.

Before I tried the whole thing with a real starter, I practiced with water, and never had a problem getting a good stir because I could see the bar being picked up and spun, but when I did it with yeast and wort, I couldn't, and had to rely on voodoo, as well as a particular clicking sound that the bar makes when it is turning correctly.

I have a variable voltage supply that I could plug the stir plate into, allowing me to reduce RPM's even more, but it is an ancient piece of Army surplus (a Variac?) and I was trying to reduce the amount of stuff that I have to drag out of the basement every time I do a brew.

I am also wondering if changing the distance between the magnets mounted on the motor might improve things. My reasoning is that by having the motor mounted magnets at a greater distance from the center of spin there might be increased leverage on the stir bar. Maybe using four magnets instead of two is the solution?

Stay tuned

 

[MaxStout]

Maybe your magnets aren't powerful enough. You mentioned using two of them--are they the button-shaped magnets? Go to Radio Shack and get a couple rare earth magnets.

You shouldn't need to use four. Two will do if properly placed. Experiment with the spacing between the two, and when you get it just right, epoxy them to the fan.

 

[Painter]

I do have rare earth magnets. Man, are they strong! I'm going to start playing around with spacing and a couple of other variables now that I have pitched the last starter that I made.

 

[fmr_army]

Painter - I have the same problem as you do. I have "solved" it by adding a piece of stiff cardboard as a spacer between the flask and the stirplate. When I make the starter wort and add the yeast, I typically tip the flask so that the bar is in the corner and thus visible. I set the flask on the plate so that the magnets grab the bar, and then gently slide the flask so that the bar gets centered. Then I plug the plate in (having set my potentiometer to the lowest setting) and gradually crank it up until it moves - and then back it off a little bit.

Not only did this take a lot of trial and error to figure out my process, but it usually takes several attempts to get the system going right. During those times, I have found that liberal use of under-the-breath swear words make me feel better.

 

[fmr_army]

Painter - I have the same problem as you do. I have "solved" it by adding a piece of stiff cardboard as a spacer between the flask and the stirplate. When I make the starter wort and add the yeast, I typically tip the flask so that the bar is in the corner and thus visible. I set the flask on the plate so that the magnets grab the bar, and then gently slide the flask so that the bar gets centered. Then I plug the plate in (having set my potentiometer to the lowest setting) and gradually crank it up until it moves - and then back it off a little bit.

Not only did this take a lot of trial and error to figure out my process, but it usually takes several attempts to get the system going right. During those times, I have found that liberal use of under-the-breath swear words make me feel better.