Stir Plates

So I am sold on doing starters...so far have done without stir plates....just the old swirl it around once in while.

I use Beersmith and it has a calculator for recommneded starter size and it indicates using a stir plate has a huge effect on required starter size.

For example....for a for a 96% viable smack pack...it says I need 2.5 litre without stir plate use and a 1 litre with stir plate.....

That is a factor of 250%

Has anyone ever counted their yeast cells to see if stir plate really makes that much difference?

Seriously though....what are your observations on this as far as how effective stir plates are and how accurate these "yeast cells required " calculators are?

I'm skeptical as well as to starter calculators accuracy. Both Mr. Malty and Yeast Calc are done using the same set of experiments as a reference, and I don't know of any experiments comparing stir plates to shaking.

I would imagine that there are a number of other factors such as temperature and yeast strain that affect growth.

Here's a blog post on calculator accuracy:
http://woodlandbrew.blogspot.com/2012/11/counting-cells.html

And a proposed experiment:
http://woodlandbrew.blogspot.com/2012/11/starter-calculators-under-microscope.html

If you want to know how many cells you have after the starter has completed, you can estimate it based on volume. It's also probably reasonable to assume that the viability in near 100%. If you are using DME to make your starter there is very little protein and you can assume 2 billion cells per ml. If it is from a mash it's more likely 1 billion cells per ml, but I have seen the vary from 250 million to 1.4 billion.

But if you really want to know, then like you said, you have to count them.
here's how I do it:
http://woodlandbrew.blogspot.com/2012/11/counting-yeast-cells-to-asses-viability.html

Instead of doing a starter, I like to reduce the amount of wort added at the first pitch.
http://woodlandbrew.blogspot.com/2012/12/no-more-wasteful-yeast-starters.html

In my experience with using my stir plate it is a very effective tool for a lot of health yeast in a short period of time. I always use a yeast calculator to get a ball park figure for yeast count and pitch rate. I've had very good luck using a stir plate for my starters. IMO its a must if u slant yeast or have a frozen yeast bank.

The stir plates function is to keep the yeast in suspension. Yeast that settles out is not doing good work and the deeper in the pile, the less. This is why sparkling wine makers "riddle" their bottles and still winemakers "battonage" (stir up the lees). A yeast cake isn't getting much done, the more yeast in suspension, the better.