WLP802 Diacetyl?

[DJ_L3ThAL]

So recently I spun up some wlp802 Czech Budvar yeast which i had under water in vials in the fridge. First step was 1.020 600mL then second was 3L of 1.037 which reduced to 2L after I learned a valuable lesson not to put a room temp stir bar in near boiling wort in the flask. Lucky my spidey senses pointed the flask away from my face as the volcanic eruption of wort sprayed half my kitchen, kettle and coffee machine. Anyway....

Starter wort at the end tasted fine and clean so pitched settled and decanted slurry at fridge temp 4C which was same as the wort temp (had cube in fridge). This was in my Chronical, first brew so used a sterilock. Set fridge to 10C and attended the case swap. During this mofox handed the bad news that sterilocks don't pass krausen gas. I came home and released the sterilock to get a LOT of pressure released. They simple don't pass ANY gas it seems.

Anyways proceeded with normal ferment, it got to terminal gravity and only odd note was I wrote down a slight sweet corn taste in the sample, but ever so slight. Otherwise tasted crisp and clean as expected. This was 97% wey premium pils and carapils step mash with Saaz hops and 90min boil.

Recently tapped keg and got a horrible eggy aroma, changed the tap and it reduced significantly. BUT there is still a slight what I'm convinced is Diacetyl flavour now. My Mrs says its bananary butterscotchy, but definitely not hefe type banana. It's going down the drain sadly as its not the clean pils aroma is expect.

This was a half batch where I saved the slurry for another full cube. Got reagent bottle out today and noticed this slight Ropey ring of yeast around the glass above the liquid level. Could this indicate bacterial infection and hence my problems and hence ditch the slurry? All good I can ferment something else and happy to buy some more yeast. Just trying to find source of the problem. Thought? Cheers!

 

[DJ_L3ThAL]

MODS - plz change title to wlp802, ta



Mods Edit - Fixed

 

[Lyrebird_Cycles]

Just to be clear: the whole ferment was conducted at 10 degrees until it reached FG?

If so that's a great way to get high levels of diacetyl.

 

[Judanero]

Just to be clear: the whole ferment was conducted at 10 degrees until it reached FG?

If so that's a great way to get high levels of diacetyl.

Diacetyl can be cleaned up by the yeast at 10c it will just take longer, if you have put it in to the keg pretty well straight after terminal gravity though that may be the cause of it; the yeast hasn't had time to reduce it.

It's worthwhile to note some strains will produce more than others, 802 is a relatively low diacetyl producer.. possible contamination?

 

[Bribie G]

I wouldn't be surprised if it's diacetyl, which tastes like Werthers butter drops.
Czech Pilsners often have a touch of diacetyl.

BJCP:
Uses Moravian malted barley and a decoction mash for rich, malt character. Saaz hops and low sulfate, low carbonate water provide a distinctively soft, rounded hop profile. Traditional yeast sometimes can provide a background diacetyl note. Dextrins provide additional body, and diacetyl enhances the perception of a fuller palate.

ed: could you give a more detailed description of the flavour? If it's still sweetcorn then that could be DMS, despite the 90 min boil.

 

[sstacey]

Don't chuck it. Keep it cool for at least a month. You might find after a couple of weeks it cleans up with the yeast reabsorbing the diacetyl. All pils beers need time for this to clear up.

 

[sstacey]

Just to be clear: the whole ferment was conducted at 10 degrees until it reached FG?

If so that's a great way to get high levels of diacetyl.

Lyrebird, can you explain why keeping at 10C throughout will give excess diacetyl? I usually ferment at 9-10 throughout and don't have a problem.

 

[Lyrebird_Cycles]

How much detail do you want?

At a basic level:

Yeast produce diacetyl and others similar compounds (collectively called vicinal diketones or VDKs) during ferment as a byproduct of amino acid synthesis. They can also reabsorb and reduce these to forms which are basically flavourless at beer concentrations (the end product is acetoin in the case of diacetyl)

The rate of production of VDKs depends mostly on yeast growth rate and amino acid metabolism*, the rate of reduction depends on viable yeast mass, VDK concentration and temperature.

At warmish temperatures they're basically balanced so the VDKs disappear almost as soon as they're formed. At lower temperatures the rate of reduction slows much more than the the rate of production, so they will still be apparent for some time after the end of ferment. If you reduce the yeast activity or its contact with the green beer in this period they will stay and give a distinct flavour which many people don't like (myself included)**. People always tell you the smell is butterscotch, my usual analogy is cheap margarine: they add diacetyl to it to make it smell buttery.

Dropping the temperature, separating the yeast or adding SO2 can all cause this effect.

As a precaution, it is normal to raise the temperature of cool fermented lagers for a period called a VDK rest. With an appropriate temperature and time (eg a couple of days at 18 oC) the increased activity will chew up the VDKs and you can go back to the original temperature. This must be done while the yeast is still active but after it has stopped growing: conventionally when about 3/4 of the fermentables are gone.

As noted above, in some cases the yeast can absorb the VDKs given enough time at the lower temperature but in other cases this is not effective (usually because the yeast falls out before the job is finished).

*There's some reinforcement effect here: lower malt modification (as is normal for pilsener malts) can lead to lower YAN which can increase the production of VDKs. A protein rest can help here as it usually improves YAN.

**True story: we used to keep the diacetyl standards (for calibrating the GC) in sealed glass ampoules in the freezer. When opening the freezer the smell of diacetyl was so strong I used to step outside the lab until the smell had passed.

 

[sstacey]

In the past I have tried diacetyl rests and didn't find it much better than my current simple method of pitching high rate of yeast to already cooled wort and fermenting at 9C throughout, with a little time in the fermenter after the primary ferment is finished. I rack to keg and naturally carbonate with sugar. I leave it cool throughout, even when it's carbonating and after a short time it is very clean. I think the natural carbonation helps, speeds up the process just from my observations. It is dead easy and no diacetyl.

 

[DJ_L3ThAL]

Thanks for replies guys!

So the brew was actually put through a D-rest for 3 days at day 12 (from 10C to 13C) after pitching (gravity was already at 1.011 which was FG). This was a 18 day total ferment. I figured because I had reached FG at 11 days into the ferment or earlier (first time I took a gravity sample) that 6 more days after that including the D-rest was enough to "mop up". I then cold crashed for 6 days and kegged.

Interesting there is no comment re: the pressure I managed to build up and ferment with for the first 2-3 days. Could pressure ferments with lager yeasts cause diacetyl over and above the norm? Or does the pressure work in reverse and allow faster fermenting with less off flavours? I'm sure it's more complicated than that but thought worth re-iterating.

I did try the trub dumping ability of my Chronical out on day 5 and got about 500mL of quite liquidy stuff, looked mostly like active yeast, so perhaps I took too much yeast out and there was not enough in there to clean up after itself?

Also another thing was as I changed from Sterilock to a blow off tube mid ferment. I completely forgot when dumping the trube/yeast to remove blow off from the starsan. So ultimately about 100mL of Starsan ended up in this brew based on what was left in my blow off jug. I pushed on and ignored this but perhaps that may be having an effect?

As for the actual problem at hand with the brew. It's more predominantly an aroma as opposed to a flavour. Just poured another glass. The aroma is what I can best describe as what I pickup in pubs that have dirty beer lines (stale and eggy), mixed with a bit of banana lolly. Just smelt some margarine side by side with the beer and it is not similar at all. This aroma does seem to dissipate as you let the beer stand. It's there slightly in flavour but I have a very decent firm Saaz bitterness that competes with it which almost makes it a drinkable brew. Perhaps it's not diacetyl that I am dealing with?

I need to clear my beer lines. They are not rancid and my other beers don't have this issue. But just to rule it out I'll do a proper PBW and TSP clean.

PS. any comment as to the yeast deposits in my reagent bottle in the photo? It smells fine when I sniff in the reagent bottle.

 

[manticle]

If it's due to infection, it's bye bye beer (it will get worse and likely other off flavours will be present) but if it's just diacetyl from fermentation, you can add an active starter to the keg and leave it for a few days. Should reduce the vdk.

 

[Lyrebird_Cycles]

The aroma is what I can best describe as what I pickup in pubs that have dirty beer lines (stale and eggy), mixed with a bit of banana lolly.

Probably not diacetyl then. Can't tell what it is without seeing the beer.

Interesting there is no comment re: the pressure I managed to build up and ferment with for the first 2-3 days. Could pressure ferments with lager yeasts cause diacetyl over and above the norm? Or does the pressure work in reverse and allow faster fermenting with less off flavours? I'm sure it's more complicated than that but thought worth re-iterating.

Pressure does weird things to yeast and it depends on the yeast and the pressure. No-one will be able to predict anything from the paucity of information given.

 

[Goose]

Just to be clear: the whole ferment was conducted at 10 degrees until it reached FG?

If so that's a great way to get high levels of diacetyl.

Its all about the yeast, no trubble.

In my humble experience, a healthy yeast will absorb AAS, the precursor to diacetyl. A weak, stressed or mutated yeast will throw AAS and not absorb it, even if you do an extended diacetyl rest.

I have found that if I am lucky (or smart) enough to have a healthy yeast and my pitch rate is sufficient, a diacetyl rest is not needed, though a precautionary temperature rise will not affect the finished beer.

thankyou, and goodnight.

 

[Lyrebird_Cycles]

That's not possible with the currently accepted synthesis pathway. The alpha aceto acids are now generally accepted as being part of the yeasts' synthesis of valine and isoleucine, hence the comment about amino acids above.

What is known is that once the cell membrane gets leaky, the ability of the yeast to uptake and reduce the VDKs is compromised. This explains the symptoms you are seeing.

 

[DJ_L3ThAL]

So I cleaned my lines with perc/met, rinsed and starsaned. Poured a couple of glasses today and the aroma is definitely still there. It's subtle compared to what it was initially, but it's no different with cleaned lines.

It's almost banana phenolic in nature but not in a nice way.

I think the only way forward is to try some fresh yeast for my full cube and let the results from that determine if the fault in this one was the yeast or starter or removal of too much yeast mid ferment as the cause.