Yeast starters, stir plates, and decanting…

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brechbräu

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Even after brewing on and off for 25 years, I still find myself with lots of questions and insecurities…

I’ve done yeast starters for years, but have never had a stir plate. I understand that stir plates increase the aeration of the wort for the starter, but I also thought all that extra aeration during fermentation also ends up souring the wort. If that is so, do you decant the extra, soured wort from the starter and just pitch the yeast on the bottom? If you accidentally pour some of the aerated starter wort into the batch with the yeast, what is the effect?

Thanks for your insights!
 
It's been a while since I've used a stir plate but if I remember correctly I just dumped the whole kit and kaboodle in . Some decant , think it depends on batch size and preference. I got hooked on SNS (shakin not stirred) starter along with the propper starter. My stir plate has been collecting dust since then .
 
If you use a liquid yeast pack, most of the time it is good to do a starter to get cell count up. Many of the dry yeasts these days do not need a starter or aeration just pitch from packet per instructions.

With any subsequent use of yeast, if saved in jar or left in fermentor as a yeast cake, yeast should be supplied oxygen in some way. This can be done on a small scale by splashing or agitating the wort before or on the way to the fermentor. With larger volumes and for more assurance, an air injector or "stone" works well. Some people use air pumps, but many serious brewers have a tank of compressed oxygen with regulator to supply an assured does of O2 quickly.

Anyway, in to answer your question; it is good for yeast to help get started with O2, but introduction of O2 after fermentation has progressed is very bad for the beer.

In short, O2 good for yeast at beginning, bad after fermentation.

A stir plate is not needed to make good beer, but probably helpful if you have a yeast bank you are working.
 
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I'm often stepping up from old yeast or small samples, Generally build to about 2 litres and then let it settle pour off most of the oxidised starter and then just swirl and pitch the concentrated yeast. Whilst retaining the magnet!!!
I do tend to taste a bit of that starter and it just tastes like oxidised flat beer. If it smells or tastes terrible don't use it.
 
If you use a liquid yeast pack, most of the time it is good to do a starter to get cell count up. Many of the dry yeasts these days do not need a starter or aeration just pitch from packet per instructions.

Any subsequent use of yeast, if saved in jar or left in fermenotor as a yeast cake, yeast should be supplied oxygen in some way. This can be done on a small scale by splashing or agitating the wort before or on the way to the fermentor. With larger volumes and for more assurance, an air injector or "stone" works well. Some people use air pumps, but many serious brewers have a tank of compressed oxygen with regulator to supply an assured does of O2 quickly.

Anyway, in to answer your question; it is good for yeast to help get started with O2, but introduction of O2 after fermentation has progressed is very bad for the beer.

In short, O2 good for yeast at beginning, bad after fermentation.
Right. I know oxygen is good at the beginning and bad thereafter. I was wondering about the starter wort only…
 
Right. I know oxygen is good at the beginning and bad thereafter. I was wondering about the starter wort only…

If it is just the starter, the stir plate should introduce enough O2. Without a stir plate, slosh it around or pour in & out of a couple of containers, in as sanitized way as practical.
 
I've been doing starters for liquid yeast like forever but in all that time only once did not decant the spent beer - and that was to pitch it at "peak krausen" to try and perk up a barley wine fermentation that had gone sluggish. Otherwise I do the starters so I can "overbuild" what I need for brewing and set the excess aside in the fridge to step up the next time I brew with that strain...

Cheers!
 
I always get rid of the starter wort (beer actually). The starter is given enough time to finish and flocculate. It then goes into the fridge until brew day which gives some leeway of a week or so. When the batch is settling after chilling, I choose to siphon away the beer on top instead of pouring. Pouring just seems like a fools errand as the yeast seem to get stirred up with the tilting. So what goes into the batch is pretty much only the yeast. I run some chilled and settled wort into the starter vessel and let it sit while I oxygenate etc... After the batch is all ready I use a magnet to get the stir bar out and I pitch.
 
Right. I know oxygen is good at the beginning and bad thereafter. I was wondering about the starter wort only…
For me...

If I am making more of a vitality starter (usually 1L or less) that is going less than 24 hours and pitched while the stater is still actively fermenting, I pitch the entire starter. My theory is that the active yeast will consume any oxygen introduced (but that might depend some on the process and equipment used).

If I am trying to build up cell counts, I will make a starter (often >1L) 3-4 days before brew day, cold crash the starter once fermentation slows, and decant most of the liquid. I would rather not add more than 1L of starter liquid and I have more concerns about oxidation in this case.
 
For light/delicate beers such as Helles that requires a huge starter, I crash and decant. It takes some planning ahead. Spin the starter 48 hours prior to brew day. 24 hours stirring, 24 hours cold crashing in the fridge. Pull it out on brew day, decant 80% of the wort off the compact slurry (sometimes siphoning is better for fluffy strains). Allow to warm during brew day and pitch the slurry.

Bold stouts and such, pitch the whole thing because it's a smaller starter and won't really be affected by a little oxidized beer.
 
I've been doing starters for liquid yeast like forever but in all that time only once did not decant the spent beer - and that was to pitch it at "peak krausen" to try and perk up a barley wine fermentation that had gone sluggish. Otherwise I do the starters so I can "overbuild" what I need for brewing and set the excess aside in the fridge to step up the next time I brew with that strain...

Cheers!
Do you leave the stir plate on and… stirring… the entire time the starter is going?
 
Like a lot of people here, I use a stir plate. I will leave it on there for a couple/few days then right in the fridge it goes. On brew day, after it settles out, I decant all the liquid, most of the trub, and leave the yeasty bits at the bottom. When filling the fermenter, I pour some wort into the flask, give it a swish and pour it in. Rinse and repeat I didn't get all the yeast.
 
I don't use a stir plate because I want to be able to agitate the flask and see bubbles forming indicating active fermentation. Not every yeast strain produces a nice white visible krausen because I use fermcap in all of my starters. Also, my instinct based on absolutely zero science and my own feelings alone, is that infrequent shaking is probably more than enough agitation.
 
I don't use a stir plate because I want to be able to agitate the flask and see bubbles forming indicating active fermentation. Not every yeast strain produces a nice white visible krausen because I use fermcap in all of my starters. Also, my instinct based on absolutely zero science and my own feelings alone, is that infrequent shaking is probably more than enough agitation.
I find it is pretty obvious when the starter turns a bit milky that there is plenty of yeast growth and fermentation is about done. Models seems to show you get about 2x as much cell growth with a starter versus intermittent shaking, so I added a stir plate to my process a few years ago. I have not done a side by side, but I am impressed by the layer of yeast I get with a stir plate.
 
If I do a starter with one of my saved yeasts...I'll decant the jar and use the mash wort and a little water to thin it out. after the brewing is over, cooled and in the fermenter...the starter usually has some activity, if not wait a day. then it all gets pitched since the starter wort was directly from the mash anyway.
 
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