why can you aerate a 5ltr starter but not a fermenting beer?

[droid]

bit confused here

building up a starter for an IPA and it looks like I am going to need 4.5ltrs (no stirrplate)

I have made a small beer from the base grain which turned out to be not enough, so I will do another one today - why is it that I can shake the shiza out of this small beer but not a full 20ltr brew

5ltrs of fermenting brew represents 25% of the total brew - why is it ok and why will this not have an ill affect on the finshed brew if it is so important to not aerate fermenting beer?

I see people talking about 7ltr starters in lagers - that could be 30% of the total brew that has been aerated while fermenting....

help a guy out

 

[sponge]

If you decant the aerated beer from the yeast then it doesn't matter. If you pitch the whole starter then it is a different story.

 

[mattlea266]

I think most people, not everyone, will let the starter settle and pour the oxygenated beer down the sink, perhaps tasting a small amount to test for off flavours. This will leave the layer of yeast on the bottom. Just leave a couple of hundred mls to swirl the yeast up with. I chill my starter down so the yeast settles out more, some people do not.

 

[seamad]

Once you start introducing O2 into a starter you end up with oxidised beer. Have a taste and you'll see why you don't want to drink it. The other alternative is to to just brew a smaller volume first without re-oxygenating thereby removing oxidation problems, bottle/keg that and then use the yeast cake for the bigger volume. I've only done this for bigger gravity beers, not volumes , but similar principle.

 

[neal32]

Because you're growing yeast as opposed to producing a drinkable beer. And yeast grow best with abundant o2.

 

[droid]

****

so the 3.5ltr starter that I poured into my urquell lager (fermenting now) was an epic fail? it should have been just the yeast

I thought I read people pitching 5ltr and 7ltr starters but obviously they were referring to just the yeast built up from the 5ltr or 7ltr starter

another misunderstanding dammit - well that's just great, its a true wonder that ive managed to navigate life to this point touch wood...lol

 

[manticle]

I oxygenate my starters only at the beginning (like beer) and use the lot when active but if you continue oxygenation well after ferment has begun, you may oxidise the starter beer. All depends on how much O2 you introduced and what stage the yeast were at (and delineation between stages is not absolute). Your urquell may be fine so don't panic yet but next time pick one: continued o2 for maximum growth, decant beer and pitch yeast slurry or o2 at beginning, pitch all at active (which works beautifully if you start with fresh, healthy yeast and same/similar wort).

 

[Danscraftbeer]

Interesting Good question. I think the reason I've got away with it is because I only stir plate for a few hours over the all grain prosses.
2 to 8 hours usually and the yeast is just reproducing/building up rather than converting to alcohol yet.
1lt starter for 38lt brew. Pitch the whole lot in.

I think this solves a mystery of a couple of Beers I've made had an off flavor after taste you get at the back of your tounge. Checking notes one of these beer starters was on stir plate for ~20 hours. The other was 3rd culture and went berserk on stir plate after only 3 hours, foam breaching the foil cap. Maybe its an example of the yeast has gone too far into the alcohol conversion stage while still being oxygenated.

 

[droid]

thanks for the replies, its appreciated