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What is the function of a stir plate when making a yeast starter?

Does it drastically improve the starter process?

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up vote 7 down vote accepted

The point of a stirplate is to help the yeast propagate by aerating the wort. Yeast Propagation and Maintainance claim stirring can increase yeast cell count by 10-15 times, compared to simply using an airlock (non-aerated) or 2.5 times the cell count of the traditionally aerated starter (aquarium pump).

It's important not to use an airlock, since the primary function of the stir-plate is to help oxygen enter the wort all the while the yeast are propagating, since oxygen is needed for yeast growth. It does this by continually agitating the wort, and so increases the rate of absorbtion of oxygen into the wort.

You can buy stirplates, but they're quite expensive, or build your own.

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I believe you'll find this link most helpful to your complex query about these mythical "stir plates". http://lmgtfy.com/?q=what+is+a+stir+plate%3F

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I realize this is tongue in cheek, but some of the links can be tricky to find. The link I posted about 10-15 times cell growth was my original motivation to building a stirplate, but it still took me several minutes to conjure up the right query to find it again. And keep in mind that it's not long before these stackexchange sites end up at the top of search results, so your answer will send anyone searching for this in an infinite loop! :) – mdma Feb 14 '12 at 22:33
If his question was something not so simple, like "how much growth occurs in a starter?" then I'd understand. His 2 questions ('what's the function', and 'does it improve the starter') are both easily answered with the simple Google search. – Graham Feb 15 '12 at 12:54
I see your point, although simple questions often have complex answers. Giggle gives a lots of information, but that's also a weakness, it can take time to sift through it all. These QA sites provide a simple answer, in context, and then link to relevant resources. I wonder if there is anything about this on meta - how simple is too simple a question? – mdma Feb 15 '12 at 12:59
What does this say about me that I'd rather take the hit on my Rep for the downvotes than remove my snarky answer...? – Graham Feb 15 '12 at 19:36
fwiw, I didn't downvote. I've raised a question on meta about this. meta.homebrew.stackexchange.com/questions/253/… – mdma Feb 15 '12 at 19:58

Basically it's a rotating magnet that forces a iron stir bar inside the starter to rotate. The rotating stir bar stirs the starter, keeping it in continuous motion.

It helps the yeast starter process by exposing more surface area of the starter to oxygen. Yeast then use that oxygen to reproduce. Since the yeast are exposed to more oxygen than they would be without a stir plate, they reproduce more.

Since the yeast reproduce more, you get a larger amount of healthy yeast using a stir plate than you would without.

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