Why Use A Stir Plate?

[bear09]

Hi All.

I feel silly for asking but why would you use a stir plate? How does it help?

Do micros use them?

Thank you.

 

[Supra-Jim]

They enable you to quickly grow a lot of healthy yeast for a good strong ferment.

Cheers SJ

 

[Pennywise]

I don't know all the science behind it but it keeps the yeast in suspension and thus promotes more activity for a healthier starter. Shaking the starter evertime you walk past it is doing a similar thing, but not quite as effective.

Edit: type too slow

 

[newguy]

I've noticed a shorter time between feeding my starter for the first time and actually pitching the starter into a batch of wort since I built a stir plate. I used to just incrementally feed a starter fresh wort and give it a shake whenever I was near. That did work fine - or at least it seemed like it did at the time. Now that I've switched to the stir plate I've noticed a marked increase in yeast slurry in starters fed with the same amount of wort pre stir plate era. As I mentioned earlier, the time between first feeding a starter and it being ready to pitch is now much shorter as well - 2 or 3 days as opposed to a week or more before.

That said, the most dramatic difference in my ferments came from using pure oxygen (30 seconds) at pitching time. That change was night & day......a very worthwhile investment in my opinion.

 

[petesbrew]

I don't know all the science behind it but it keeps the yeast in suspension and thus promotes more activity for a healthier starter. Shaking the starter evertime you walk past it is doing a similar thing, but not quite as effective.

Edit: type too slow

That's my method, the shaking.
Yeast cultivation is all a bit of luck at my place, so the more info on how to use stir plates here, the better.

Another question, how do you get out the little stirbar at the end?

 

[newguy]

Another question, how do you get out the little stirbar at the end?

Big magnet. Place it on the bottom of the flask, then slowly run it up to the mouth. The stir bar will follow it, finally "jumping" out of the flask once you get the external magnet near the mouth.

 

[komodo]

New guy - where do you get pure oxgen from? Im assuming you must have an oxy/acet set?
I read somewhere that you could get pure oxygen in a cannister like mapp gas - but ive never seen it?

Edit just realised your from canada so probably not gunna be much help with info on where to get it locally LOL

 

[Supra-Jim]

A quick summay of the 'science' behind it.

The stir bar keeps the yeast in suspension and mixed up with the sugars. The vortex generated by the spinning stir bar helps to drive off CO2 and pulls in oxygen (you don't fully seal a flask on a stir plate). When yeast have oxygen present they remain in the "eat sugar and mulitply" phase of their life. Hence you end up growing more yeast.

If you weren't driving off the CO2 you would quickly have a CO2 rich environment (similar to your wort) and the yeast would switch from growth phase to fermentation phase. You don't want them fermenting the starter as this can tire them out and you end up can with lethargic yeast in your wort.

Shaking a starter vessel intermittantly simulates what a stir plate does (and it a very simple device) but it does not work as quickly or effectively as stir plate.

Another reason for using a stir plate is to get the correct amount of yeast for a given wort/ferment. Check www.mrmalty.com for info and a helpful calculator.

Cheers SJ

 

[rich_lamb]

The stirbar does force the yeast to stay in suspension which might help attenuation in the starter - but that's not really important for starters.
Moreover it helps remove dissolved CO2 buildup from the starter and keeps dissolved oxygen up; if you ensure your starter has a loose-fitting lid (typically a piece of alfoil scrunched over the top). This is better for yeasties to breed.

So the short answer is that a stirplate increases your yeast population for a given starter. I notice about a 2X increase, but others will have different mileage.

 

[altstart]

I use pure oxygen Ross @ Craftbrewer has it and the S/S diffuser.
Cheers Altstart

 

[Pennywise]

If air is being sucked back into the flask, wouldn't there be a much higher chance of infecting the starter?

 

[therook]

I use to use a stir plate but have gone back to just shaking the bottle and haven't noticed any difference, just a longer time to get the size you want

Rook

 

[newguy]

New guy - where do you get pure oxgen from? Im assuming you must have an oxy/acet set?
I read somewhere that you could get pure oxygen in a cannister like mapp gas - but ive never seen it?

Edit just realised your from canada so probably not gunna be much help with info on where to get it locally LOL

I get mine from Home Depot - I imagine that any similar home improvement/hardware store there should have it as well. I got the small regulator that's machined to fit the small 40g O2 "industrial" cylinders. Barring that, befriend a paramedic or someone in the homecare field. They may be able to source a used medical oxygen canister.

 

[Supra-Jim]

If air is being sucked back into the flask, wouldn't there be a much higher chance of infecting the starter?

Like everything yeast related you need to be careful about infections. However in the starter liquid you have a very high proportion of active yeast to a small volume. This should help to overcome/overpower any nasties that may get in. Ideally it should kept in a clean area.

Using an airlock will seal the flask one-way, and allow CO2 out but will not allow air/oxygen back in. I use alu foil loosely pressed over the mouth of the flask. I put the foil on prior to boiling the flask so it gets sterilized at the same time.

Cheers SJ

 

[Rodolphe01]

By no means an expert, and haven't even used a stir plate - but wouldn't the fact that CO2 forms a blanket stop air 'getting sucked in', sure it will get CO2 out of solution because of the agitation, but i doubt it would introduce 'new' O2, of course it may well alter the ratio of CO2 or O2.

 

[mika]

If air is being sucked back into the flask, wouldn't there be a much higher chance of infecting the starter?

With a stir plate you're not looking at sucking air in and out, it's more about an exchange with the oxygen in the flask. As the yeast produce CO2 as they're metabolising I'm not sure that the oxygen over the liquid hangs around for all that long, yet as others have mentioned, I have experienced a greater yeast growth in the flask prior to using a stirplate.

One thing that has got me a little worried recently is the possibility of air being sucked in as the flask/wort is cooled. I think I heard on the latest Session by the BN that one guy had moved apartments and had infection problems only to discover it was occurring even in his yeast starters, with a possibility being bacteria rich air being drawn into the flask. Though as I type this I do wonder if it's one of those self healing processes, where air is drawn in, but the flask is still quite hot and the cooler it gets the less air it draws in... if you get what I'm saying.
I wonder whether a spray of the room, where the flask is cooled, with one of those air fresheners that claims they sanitise would do anything for you, on the off chance that you do have a lot of wild yeast present. Or would your starter end up with a lavender aroma :huh:

 

[Pennywise]

Ahh, that makes sense, bit like the chances of getting an infection after fermentation is less than before, but with starters it's yeast population rather than alcohol in the actual beer. Cheers SJ, for a second there I was thinking if it's worth the risk using a stir plate.

Edit: mika, I never even jerried about the air being sucked in whilst cooling the flask, I spose if we don't get an infection then the chances of it happening while the yeast is growing is slightly less.

 

[Phoney]

New guy - where do you get pure oxgen from? Im assuming you must have an oxy/acet set?
I read somewhere that you could get pure oxygen in a cannister like mapp gas - but ive never seen it?

Edit just realised your from canada so probably not gunna be much help with info on where to get it locally LOL

BOC gasses. Lookup retailers in your local area, there should be dozens of them.

https://boc.com.au/irj/portal/anonymous?guest_user=australia

 

[komodo]

I dont really need a full size bottle like AirLiquide or SupaGas or BOC would want to rent me. Hence wanting one like a benzomatic mapp gas canister.
I could alway borrow a bottle of oxy from work (I manage a fairly large structrual steel fabrication workshop) - but thats not convenient like a small disposable canister would be.

 

[mika]

Bunnings should be able to special order the Benzomatic oxy cylinders for you, prob around $40 a pop, but should last ~20brews or there abouts. Need to purchase a reg from Morebeer.com in the states though, but they're fairly cheap.

Edit: There's a dude in perth who flogs them as well, would have to find his name, PM if interested. Don't know whether he'd be able to ship them to you though.