# WY1469, Acetaldehyde, top cropping a bad idea?



## squirt in the turns (22/5/13)

I cultured up some WY1469 West Yorkshire Ale yeast from a minuscule amount I had stored in a stubbie under sterile water since October last year (7 months old). I built it up to a 2 litre starter which fermented out and tasted fine when I poured off the beer. Anyway, I pitched it into 20 litres of 1.045 wort, which apparently was too much for it as I'm pretty sure it's got some major acetaldehyde issues. I've never smelled/tasted it before in my beers or any others, but it meets the "green apples" description normally given. 2 uninitiated non-brewer friends said it smelled "cidery", SWMBO said "socks" (which was wrong).

2 questions:

1) If this is indeed acetaldehyde and is due to under-pitching, will it clean up given time? It's pretty noticeable at this stage.

2) I pitched 4 days ago, and there's a typically WY1469-like large, persistent, creamy-looking krausen which I was intending to scoop up and chuck into another batch today. I imagine it's pretty difficult to under-pitch if I just grab a heap of krausen, but is this stressed acetaldehyde-producing krausen less healthy, even tough it looks dense and awesome? Or is it possible that by taking enough to inoculate a new batch, I'll deprive the original batch of enough yeast to fix itself?

Cheers all!


----------



## manticle (22/5/13)

Acetaldehyde is a natural part of fermentation so yeast producing it should still be OK to pitch into another batch. However, why not top crop into a starter, get it to high krausen and see how it smells/tastes? Have a back up on hand for Justin.


Contact with healthy yeast and time should be enough to reduce it in the batch you have. Keep it reasonably warm and taste it every couple of days to see if it is reducing. If not, it may have another cause (eg. oxidation)

If it doesn't seem to be fading with time, you could top crop back from your second batch (I did something like this recently to reduce diacetyl in a lager).

I get more of a paint emulsion and pumpkin skin note from acetaldehyde than I do green apple (have got the apple but the others are more recognisable for me). I don't find any relationship to cider.


----------



## verysupple (22/5/13)

To answer Q1: I haven't had bad acetaldehyde since my kit days before I knew what I was doing, but from those experiences I believe it will clear up given time.

As far as Q2 goes: If you top crop you will have plenty of yeast left for that bacth. However (without professing to be an expert), I have the same reservations as you. That is I believe if the yeast were unhealthy when you pitched them this time, you may not end up with a healthy pitch for the next batch. Or at the least you will have selected (repitched) far from optimal yeast.

My 2c: In a homebrew/non ideal lab situation it seems unlikely that the culture was of either acceptable viability or vitality after 7 months (this would be really pushing it for a commercial scale yeast lab). I'd give up on that culture and start again.

EDIT: I think I agree with Manticle with regards to duration in contact with healthy yeast - although I disagree with him with regard to the perceived off flavours of acetaldehyde. I totally got cidery tangs. My experience of acetaldehyde was mainly due to poor fermentation temp control. This now leads me to believe that the acetaldehyde you got was maybe not from a yeast pitch of poor health. The current batch should be fine given time. However I still wouldn't be harvesting it for a new batch.


----------



## squirt in the turns (22/5/13)

Thanks for the replies guys.

I'll just let the first batch go until the aroma sorts itself out - hopefully it will. The second batch is cubed so no rush. I'll just use something else when I pitch it.

It's got some painty/solventy notes too, so I'd say it's definitely acetaldehyde. My friends are cider drinkers so it makes sense that they'd draw that parallel. I simply smelled it and thought "hmm, that's not right" and started thinking about which description of off-flavours it matched,

It's been undisturbed and sealed with gladwrap as per standard procedure so I doubt oxidation is the cause of the issue. Hopefully not an infection.


----------



## manticle (23/5/13)

When i say 'I get this flavour' I don't mean that is the only flavour to be perceived and all other descriptions are wrong.

Various compounds are perceived differently according to their concentration, the palate of the person tasting (and the psychological associations they make) and possibly the beer they are in.

Even the same beer, dosed with acetaldehyde will taste very different 30 minutes later. I didn't mean to suggest that the cidery descriptor meant acetaldehyde wasn't the culprit.


----------



## squirt in the turns (23/5/13)

Just thinking about your comments on temperature, verysupple. Cidery (not necessarily acetaldehyde, though?) is usually associated with fermenting too warm, right? If anything, I'd say this batch might've been a little too cold, hovering around 17. I've found in the past that 1469 is a fast worker, and I've never had it throw any off flavours at any stage. It's pretty much at FG already. Only the aroma is inconsistent with previous experience.


----------



## Lecterfan (23/5/13)

I've recently had 1469 throw acetaldehyde. It was Manticle that helped me identify it - and while for me it was quite 'green-apple' ish and a kolsch that had a similar problem was certainly 'cidery' due to the green apple flavour - it was evident on the night that the descriptors that Manticle gave me, particularly the pumpkin skin, made a lot of sense also.

In the worst of the brews with it, it was the first batch of 1469 from a smack pack and I was a bit lazy with my starter process (never again!).

I've not had it from top cropping, but if anything my top cropping procedures (which is generally straight from the fresh fermenting wort to the new batch) are slightly over-pitched. 

As a side note I have stopped top cropping and continue to harvest from the trub either washed if storing or unwashed of pitching on the same day.

A 'miniscule' amount built up to 2L might not have produced enough yeast numbers to deal adequately with your wort, thus the yeast stress. Mr. Malty often recommends up to 3.5 or 4L starters from smack packs that are only 2 months old...food for thought.

Shit of a hobby this, there's always something else to get wrong (and I always seem to find it hahaha). :icon_cheers:


----------



## drsmurto (23/5/13)

If the acetaldehyde doesn't go, you can 'remove' it with potassium metabisulphite.


----------



## manticle (23/5/13)

I hate sulphites so it's not a method I'm likely to use but purely from interest - roughly what dose? Added as campden tablets or in a solution?

How does the k-met bind with acetaldehyde (or does it encourage the transformation to ethanol?)


----------

