Stir Plate

Yeast make the beer. As brewers we go to extremes to keep the yeasties happy. Primary purpose of starter is to insure proper health and quantity. Primary purpose of oxygen is to make sure those little guys finish their task. You are asking the right questions. Here is a better recap than I can provide:

http://www.mrmalty.com/starter_faq.php
http://www.mrmalty.com/pitching.php
https://www.wyeastlab.com/hb_oxygenation.cfm

And even though you didnt ask, here's what is going on in your primary:
https://www.morebeer.com/articles/conditioning

 

Unless you severely over pitch, more propagation also happens in your beer wort. The cells need sterols (built using oxygen) in order to do that.

ETA: Compare the volume of yeast sitting in the bottom of your fermented starter to the volume of yeast sitting in your carboy/bucket after fermenting the main batch.

 

http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/

It's more on the lines of the original gravity of your beer than a certain style.

 

There are several on line standalone yeast calculators to help with that. Or you can get brewing software (some free) with an integrated yeast calculator.

 

I've made a lot of good beers over the years without a stir plate ( I still make starters without one) and without adding pure oxygen.

 

That's not going to happen. Overpitching at the homebrew level is not likely and might not even be possible. Don't sweat over pitching. UNDER pitching is a thing though.

Mr Malty is a popular site.
Pitch rate is determined by OG and FG. The bigger the beer, the more yeast that are required to get the job done well. One technique used by a lot of us is to brew a lower abv beer with the desired yeast strain followed by the higher abv placed right on to the yeast cake. You do want to avoid mixing your beers, but to go from a pale ale to a DIPA is typical. Even with a stir plate it can be hard and time consuming to get the required cell count for a particularly big beer.

Cheers.

 

I guess if you mean it's hard to overpitch to the extent that you'll make undrinkable beer, I would agree. But it's easy to pitch so much yeast that (for example) you suppress the ester profile. If that's the goal, then it's not over pitching, but if it wasn't the goal, I'd say it was over pitching.

 

I would disagree with this. I pitched wort onto a yeast cake once and the beer was terrible. I know it was the yeast that made it bad, because I then pitched the same yeast after harvesting, at more of an appropriate rate, on two different worts and both turned out bad (lacking esters) like the parent beer.

 

I'm saying that unless you are doing advanced yeast tricks such as fiddling with the ester profile you are beyond yeast 101. The vast majority of brewers, professionals as well as homebrewers, are looking to pitch an adequate amount of yeast to obtain the desired and typical characteristic from the particular yeast strain. It is difficult to step up a starter with a stri plate to the volume needed to get to over pitching.

But yes, if one of your goals is to stress the yeast or have a very quick full fermentation than over pitching is something to watch out for. A brewer should be well versed in yeast management by that point.
Cheers.

 

Use lower speeds. Seriously, all you need to do is keep the wort moving.

 

how long do you usually keep the stir plate on for?

 

I usually go about 24 hours for room temp (~70F) starters. But some yeast strains and starter sizes tend to be a little slower or faster. You can often tell by the color of the wort/beer (and thus the density of the yeast cells) how it's coming along. You can also measure the gravity, but I confess that I don't do that for starters anymore.

 

how do you tell by color? is it darker, lighter, etc?

 

I'd call it cloudier, which can appear "whiter," when the yeast is denser.

 

I run mine until the yeast tell me they are finished. Typically you'll have a krausen and over time it will fall. It's okay to cut off the stir plate for about 45 minutes and let things settle down. Then give it a hard shake . . . if you get bubbles the little guys are still producing (CO2 off-gassing as a result of yeast cellular respiration). After it's completely finished I normally let it run another couple of hours.

Randomly some starters make little (or no) krausen, yet they are still growing. The stir-bar is off-gassing the CO2 as it is produced so no noticeable bubbles. Same approach here, give it a pause then a hard shake to confirm it's still working. My experience is 18 - 36 hours to do the job. After a longer pause you should notice the yeast solids collecting at the bottom, it should be obviously more than when you started. I have a 100ml mark on my flasks for reference.

 

Not to hijack but looking into stir plates for starters any suggestions I would like to keep it as low as possible budget wise while still getting a durable effective stir plate. Also 1L or 2L erlenmeyer?