Yeast starters and oxidization

[mosto]

I've searched AHB and the net in general but haven't find any real consensus on this, so I thought I'd start a thread.

I've come up with a process for my brewing which ties in well with the limitations of my equipment, and I'm happy with the resulting beer, but a bit I've read lately has me wondering are there flaws in my process, particularly around my yeast starter.

I BIAB in a 38ish litre crab cooker. I don't insulate it, rather I plug it into a STC and put the probe in the mash. This seems to work ok as the temp varies only a degree or so either side of my targeted mash temp. I happy with this setup but thought I'd put it in to see if anyone can see any massive problems with it.

I aim for 20L into the fermenter, which is a 20L water jerry from Bunnings. I like these as I can fit two side by side in my ferm fridge.

I no chill and use the 15L cubes (actual cube shaped) water drums from Bunnings. Filled to the brim I get 17-18L in there. The remaining couple of litres I draw off and use for a starter. I put the starter on my stir plate as soon as it's cool enough to pitch. It usually takes a couple of days to reach high krausen (it isn't a very vigorous stir), then I pitch the whole starter into the wort and put into the ferm fridge. By pitching the whole starter I get back up to my 20L volume which is a perfect batch size for me as I keg.

My main query is am I risking oxidization with my starter? I've never picked up any of the flavours described as oxidization in my beer, but I have only been using this process for 2-3 brews.

Any constructive input would be appreciated.

 

[manticle]

Taste the starter. The risk is there but if you're not picking it up in the starter or beer then why worry? I do similar but without the stirplate. Less cell growth than you would get but the yeast is fresh, pitched to identical wort and pitched when active which are all beneficial.

 

[Black n Tan]

Your starter will be oxidised, taste it. If you pitch the whole lot you have the potential to add off flavours to your beer and/or reduce the shelf life. It may takes months to taste the difference. White and Zainasheff in the Yeast book recommend decanting the spent wort and pitching just the yeast if the starter is more than 5% of the wort volume. My starters are always more than 5% so I follow their advice and pitch just the yeast. I think it is more important with delicate beers or when the starter is big, such as for lagers. My beers are better than they were a year ago when I used to pitch the lot, but I have had other process improvements during that time, so can't definitively say that is the reason or the improvement.

 

[Screwtop]

Your starter will be oxidised,

Well.................... maybe, slightly. Yeast requires oxygen during the growth phase, however if you make a 2L starter using a full healthy pitch of 100 billion cells there is not going to be much growth. Why? because yeast bud or multiply depending upon the concentration of sugar they are introduced to. In very basic terms it comes down to how many cells are introduced to a particular volume of wort of a particular gravity. if there is a high concentration of sugar in wort contacting the yeast cell wall then the cell will produce multiple buds. The lower the concentration of sugar the less budding. So pitching 100 billion cells meant to be pitched to 19 odd litres of wort into 2L of wort, very little budding/growth is going to take place. Due to the number of cells in such a low concentration of sugar the cells will most likely begin stage 2 fairly soon after pitching.

So, forget waiting for krausen. Wait until the starter wort is simply - "ACTIVE" (look for bubbles of Co2 through the wall of your starter vessel) maybe around 12+ hrs, then pitch the lot! No risk of oxidation.

I use the same process as you. I remove some wort from the kettle on the way to the fermenter. Wait for it to cool, pitch, then shake a few times (way over stirplates and aeration, have done all of that) and wait until the starter is really active before pitching. A starter is just that, a small batch of already fermenting wort, pitched to the main fermentation to provide a big healthy yeast colony to kick off fermentation.

Well Done!

Screwy

 

[Black n Tan]

Well.................... maybe, slightly. Yeast requires oxygen during the growth phase, however if you make a 2L starter using a full healthy pitch of 100 billion cells there is not going to be much growth. ...
So, forget waiting for krausen. Wait until the starter wort is simply - "ACTIVE" (look for bubbles of Co2 through the wall of your starter vessel) maybe around 12+ hrs, then pitch the lot! No risk of oxidation.

Sorry just trying to understand this, are you saying that the starter will not be oxidised because the yeast are active and consuming the oxygen introduced by stirring or have I missed something. White and Zainasheff seem to believe the starter will be oxidised and not taste very good and to avoid adding the whole starter if more than 5% of wort volume.

 

[mosto]

Thanks for the info all. Next starter I'll have a taste. I assume if it's oxidized the taste will be pretty unmistakable, I've read it's a cardboard/paper type taste?

If I need to ditch the starter wort and just pitch the yeast, I'll have to see if I can squeeze a bit more volume from my pot to get up to my desired batch volume. I'll also need to find bigger cubes as the ones I use now hold 18L max.

 

[Screwtop]

Sorry just trying to understand this, are you saying that the starter will not be oxidised because the yeast are active and consuming the oxygen introduced by stirring or have I missed something. White and Zainasheff seem to believe the starter will be oxidised and not taste very good and to avoid adding the whole starter if more than 5% of wort volume.

What is the cause of oxidation in wort on a stirplate?? A clue can be found in the first paragraph on page 138. They refer to a starter which has been left on the stirplate well past stage 1, until the yeast has consumed all of the wort sugar (phase 2). Wort aerated or oxygenated past phase 1 will be oxidised. (Line 5 the starter liquid doesn't taste great. Check White and Zainasheff re introduction of O2 into wort, never after phase 1 (Aerobic/growth phase) 24hrs would be rule of thumb. Oxidation occurs wher e the starter is left on the stirplate for the full term of fermentation. Warm wort being aerated over time will result in oxidisation.

To understand the first paragraph of my reply post read page 141. There is much confusion among homebrewers between what is a starter and what could be more accurately described as yeast propagation.

Growing/propagating yeast by inoculating a small batch of wort (maybe a litre or two) at a rate calculated (by design of by accident) to maximise growth then allowing the wort to ferment out, dropping out in the fridge and then pitching the "YEAST"............... is pitching "YEAST" not a starter. A starter is a small batch of fermenting wort

Making a small batch of fermenting wort (two to four litres for a 20 litre batch) using a full 100 billion cells (if the yeast is fresh) and pitching all of it while active in Phase 2 (fermentation phase, after 12 to 24 hrs) is pitching ...."STARTER WORT"

Check out Yield Factor in the book, for an understanding of what I was referring to, have a look at the table on page 140. Pitching 100 billion yeast cells (one vial/pack) to 1 litre of wort (100 million cells/ml inoculation rate) results in an increase of 52 billion new yeast cells, a doubling of only .5 times. However pitch a pack to 8 litres of wort (13 million cells/ml inoculation rate) results increase of 300 billion new yeast cells, a doubling of 3 times.

Some more reading: http://aussiehomebrewer.com/topic/74794-nhc-2013-kai-troester-braukaisercom-on-stirplate-starters/?p=1069192

Cheers,

Screwy

 

[Black n Tan]

Thanks Screwy for the education. Yes para 1 of page 138 does talk about fermenting out. I think I get what you are saying about pitching the whole lot before sugars are consumed, but of course it raises another question from me. Why do most brewers and books recommend not letting oxygen into a batch of beer (not a starter) after the first 24 hours, when it will continue to be in phase 1 for sometime afterwards? This does suggest that oxidation can occur in phase 1, yes? Is it the fact that you dilute the starter so a little oxidation is unlikely to taint the beer? Is there a limit to the size of the starter before you would consider just pitching the yeast.

 

[Batz]

Good little clip from the White Labs guys.


http://www.youtube.com/watch?v=1zUYxb-_B8A

 

[Online Brewing Supplies]

Typically in a brewery situation the starter would be oxidized and unusable, the wort that is.
The yeast then would be separated from the wort and either pitched or re fed.
Nev

 

[Screwtop]

Thanks Screwy for the education. Yes para 1 of page 138 does talk about fermenting out. I think I get what you are saying about pitching the whole lot before sugars are consumed, but of course it raises another question from me. Why do most brewers and books recommend not letting oxygen into a batch of beer (not a starter) after the first 24 hours, when it will continue to be in phase 1 for sometime afterwards? This does suggest that oxidation can occur in phase 1, yes? Is it the fact that you dilute the starter so a little oxidation is unlikely to taint the beer? Is there a limit to the size of the starter before you would consider just pitching the yeast.

I remember asking that same question of Dave Logsdon many years ago, his answer........ "a good rule of thumb is not to oxygenate after 24 hrs from pitching". So I guess the yeast cells have taken up as much oxygen as will be useful for cell budding in that time, any later and additional O2 may not be used up by the cells and consequently result in low levels of wort oxidation.

Why not do what I do/have done. Shoot an email to Jamil, Chris White/Whitelabs or Wyeast since Dave is now in the brewing game with his new Farmhouse Ales venture. Most are happy to help, way better advice than you'll receive from me or on AHB !

Screwy