Tight Arse Stir Plate

[sosman]

In a related thread you talked about not exceeding 5m/s for stirring. Not sure if I've done my calculations right but would this mean for a 40mm stir bar, you would need to keep the rpms down to 1590 and for a 70mm stir bar 910rpms?

How do you know what rpms the fan is turning at? Is it as simple as if the fan is rated at 3000rpm at 12v, then it would be 1500rpm at 6v? I have no idea but I bet it's not this simple.

[post="67847"][/post]​

I was just parroting something Pedro mentioned. To be honest, I don't take too much notice of "magic numbers" in brewing, they are ballpark figures, probably dreamed up by some dude in a white lab coat who has never tasted a beer in his life.

Please don't infer that I think Pedro is a wanker, it is just that I have violated many other "rules" in brewing and still managed to make decent beer.

As for calculating it, I believe the 5 m/s was referred to in the context of yeast not liking excessive shear. I imagine that in the bulk of the spinning wort, the shear would be very low since the flow is uniform. I am guessing that at the interface to the stir bar and the flask (presumably at the widest point) would be where the shear is greatest.

For a brief moment of insanity, I pondered the calculations myself and then snapped back to reality as I realised that relating the numbers back to beer quality would probably be tenuous indeed.

I like to stir mine vigorously early, to get air in to the wort. Later on I am more interested in keeping the yeast in suspension and encouraging CO2 out of solution so I turn it down.

Perhaps Pedro could point us at some literature that has done all the hard work for us.

cheers

 

[Darren]

MAH,
I would aim for no more than about 500rpm no matter the size of the stir bar. 8 spins a second is more than is needed.

Slower is better than faster. Excessive speed will cause foaming of protein and is likely to kill many a yeast cell

Another point is that I have seen many a stir-bar go through the side of a flask when spun at high speed.

cheers
Darren

 

[PeterS]

I managed to follow some very helpful advice and I now I also have a Stir Plate of sorts. Although it does work, I can not yet use it for the purpose it is designed as I have not got a suitable flat bottomed vessel. I thought I make it than find out if what I got that might be suitable. Unfortunately none of my 2l or 5l containers are sufficinetly flat for it to stay in the middle. If I use a flat bottomed ice cream container just to try it, it is fascinating to see the little white flee going round and round. Any helpful hints as to where I might purchase a suitable vessel for this?

Whilst I am at it, I do have another slight problem. The pot that I am using is 500 ohms. I find that it does not give very much leeway as far as controlling the speed. If I change the pot to a smaller value thereby less resistance, would I have greater control of speed or less? (I used two rare earth magnet by the way and a 9v power source)

Thanks for your help in anticipation.

:chug:
PeterS....

 

[ozbrewer]

i found the same thing Peter, I have a 1k pot here im going to play with and see what happens


Also I have some 250ml flasks spare if you want 1, they are a little small but got to start with. I have been using shcot botles and they seem to work

 

[PeterS]

i found the same thing Peter, I have a 1k pot here im going to play with and see what happens


Also I have some 250ml flasks spare if you want 1, they are a little small but got to start with. I have been using shcot botles and they seem to work

[post="70062"][/post]​

Oh hum. You think that by introducing more resistance, you will slow it down? I guess it makes sence, but I wonder will it allow a wider control over speed? Let me know when you tried it as I have no idea in these matters. (I=E/R)

And thanks for the offer for the 250ml flask but I think it is a wee small for a 1.5 - 2L starter and plating for me is still a ways off..

:beer:
PeterS....

 

[Linz]

Peter,

A fellow brewer ordered some thick walled beakers from a chap on ebay for a reasonable price. I bought some 2 lt erlenmeyer(sp?) flasks from Livingstone and were as thin as glass could get and cracked first time out.

 

[pint of lager]

I have 10 erlenmeyer flasks of varying sizes from Livingstone, The 100 ml and 250ml sizes get lots of workouts in the pressure cooker, haven't broken one yet.

A couple of the bigger flasks have seen action on the gas top stove, but have changed the starter regime, and they now sit in the cupboard, dusty.

Do be gentle with them as they are glass, and keep thermal shocks to a minimum. That is, don't take it straight off the stove and place on a cold bench.

 

[PeterS]

I have 10 erlenmeyer flasks of varying sizes from Livingstone, The 100 ml and 250ml sizes get lots of workouts in the pressure cooker, haven't broken one yet.

A couple of the bigger flasks have seen action on the gas top stove, but have changed the starter regime, and they now sit in the cupboard, dusty.

Do be gentle with them as they are glass, and keep thermal shocks to a minimum. That is, don't take it straight off the stove and place on a cold bench.

[post="70295"][/post]​

Thank you POL and everybody else who responded. It looks like Livingstone got another customer.

:chug:
PeterS....

 

[homebrewworld.com]

I done about half a dozen stir plate jobs and resorted to using a s.s. saucepan on my stove for boiling the wort, then cool and transfer while aerating to a beaker (thick glass flat bottom) and yeast then onto the stir plate.
I broke 1 erlenmeyer, & 1 beaker putting them on my stove.......... :angry:
Anyway, my yeasts go off better than the 'Discovery'
:beerbang:

 

[Darren]

I done about half a dozen stir plate jobs and resorted to using a s.s. saucepan on my stove for boiling the wort, then cool and transfer while aerating to a beaker (thick glass flat bottom) and yeast then onto the stir plate.
I broke 1 erlenmeyer, & 1 beaker putting them on my stove.......... :angry:
Anyway, my yeasts go off better than the 'Discovery'
:beerbang:

[post="70326"][/post]​

I would recommend that you don't place Erlenmeyer flasks directly onto electric hot plates. Unless the heat is very even they can break. When they do break they make quite a mess and the pieces are very sharp.
cheers
Darren

 

[GMK]

OK

Thanks to Hoops and DOC for getting the parts...

Here is a pic of Magnetic Stir Plate in action for the first time.

Using it to build up a starter of 1026 Cask ale Yeast to pitch in DOC's Strong Ale Recipe.



will post a pic later showing the yeast...

 

[PeterS]

OK

Thanks to Hoops and DOC for getting the parts...

Here is a pic of Magnetic Stir Plate in action for the first time.

Using it to build up a starter of 1026 Cask ale Yeast to pitch in DOC's Strong Ale Recipe.

will post a pic later showing the yeast...

[post="72784"][/post]​

Good one Ken. I am nearly there. Unfortunately, I have not got a suitable flat bottomed flask yet. In the process of evaluating options what and where to get it from. Batz brew day got me into this, now I find myself doing a lot of immitating, March pump, Stir Plate, etc. Sun Dial is next I think...You done it again Batz and thanks..

:beer:
PeterS....

 

[sosman]

I bung my 250 mL flask with wort and aluminium foil over the top into the pressure cooker for my first step up from a slant.

Then I go straight to a 2 L flask which I just sanitise with my favourite sanitiser.

 

[Batz]

OK

Thanks to Hoops and DOC for getting the parts...

Here is a pic of Magnetic Stir Plate in action for the first time.

Using it to build up a starter of 1026 Cask ale Yeast to pitch in DOC's Strong Ale Recipe.

will post a pic later showing the yeast...

[post="72784"][/post]​

Good one Ken. I am nearly there. Unfortunately, I have not got a suitable flat bottomed flask yet. In the process of evaluating options what and where to get it from. Batz brew day got me into this, now I find myself doing a lot of immitating, March pump, Stir Plate, etc. Sun Dial is next I think...You done it again Batz and thanks..

:beer:
PeterS....

[post="72800"][/post]​

I am glad to help Pete...I think :huh:

I suppose you want a Banjo dog now as well?

Batz

 

[ozbrewer]

if you cant get a flask cheep enough, try a mason jar/pasta sauce bottle....not ideal but i have used them for the last month or so , and its all working fine

 

[PeterS]

if you cant get a flask cheep enough, try a mason jar/pasta sauce bottle....not ideal but i have used them for the last month or so , and its all working fine

[post="73092"][/post]​

How many Pizzas do I need to buy to use the sauce in the bottle?

:beer:
PeterS....

 

[Plastic Man]

possible cheap heater for a DIY incubator.

http://www.oatleyelectronics.com/kits/k145.html

 

[Plastic Man]

I was having a quick look through the Oatley Electronics Kit listing to see if they also did a temp logging device in ref to Andrews great post, (couldnt see one). Has some interesting cheap temp controllers though.

But one mentioned that it was not suitable for Peltier devices. I didnt know what these were so did a quick google. Interesting devices. These would make great small heaters for a fermentator or incubator. Is anyone using them.

This next post was pretty interesting. A guy used one to keep his beer cold in the sun.

http://www.stud.ntnu.no/~arnesen/peltierbeer/index.html

Also these next two had some good basic info on what Peltiers are.

http://www.electronics-cooling.com/Resourc...96/sep96_04.htm

http://www.peltier-info.com/info.html

 

[pint of lager]

Sunday's job in the shed was to make a stirplate.

An old hard drive was sacrificed for magnets and an old pc power supply was ratted for a fan. There was a decent plastic hobby case lying around doing nothing.

First off, two magnets were glued on. This failed, the stir bar jiggled up and down, but didn't spin, no matter what volts were applied across the fan. So the magnets were ripped off and only one reglued in the centre. Success.

At about 4.2 volts, the stir bar created a nice vortex in 800ml water in an erlenmeyer flask.

Woo hoo.

 

[redbeard]

Good stuff PoL. Nothing like ripping thru old pc parts & re-using them. Perhaps the 1st 2 magnets were 2 close together ?

cheers