Acetaldehyde Question

[danwlx]

Hi all,

I have about 50 brews under my belt and thought i was getting fairly good at this game but pride comes before a fall and all that!

2 brews ago i had my first lost batch due to infection, i binned fvs and syphons as a result. My a latest brew however is currently showing lots of acetaldehyde after 12 days in the FV, now ive never had this before. The latest brew is a pale ale
mashed at 66c and fermented at 21c. The yeast used was one packet of 5 month old NBS Ale Yeast 2 and the OG was 1.047 and has stopped at 1.016 (i was hoping for nearer 1.010). I have moved to using an immersion chiller for this brew (always going for the ice bath method before) and have just started using a tube heater in my fermenting fridge rather than an aquarium heater in builders bucket approch.

Any ideas what is causing the acetaldehyde? My concerns are:

I may be getting less aeration now that i am just dropping cooled wort from the boiler into the FV (previously went fir a double transfer between to FVs with taps.

The yeast health (or could it be a characteristic?)

The tube heater overheating the yeast. My tube heater is below a reinforced glass shelf which the FV sits on.As my temp probe is positioned and insulated on the top of the FV, could the yeast of overheated causing the off flavout?

All ideas and help gratefully received!
Dan

[keith1664]

I personally would go for a lower temperature (18) and leave it for longer. My current practice is to pitch at 17-18 degrees and after 5-7 days start to increase temperature to ensure full attenuation. Leave it another 7 days then I'll then crash cool to drop out the yeast. Acetaldehyde iirc is normally cleaned up by the yeast if it's left long enough.
Best practice for aereation involves an o2 cylinder, not something I've started yet though it's in the pipeline, currently I balance the fv on a piece of 3x2 and rock the buggery out of it, that's about as good as it gets without oxygen.

[MTW]

You seem very sure that the off taste is acetaldehyde. If the Fv has been directly on a glass shelf and heated from the bottom (where much of the yeast may be), with little air flow upwards around the edges of the FV, it's possibly fusel alcohol you're tasting (nail varnish remover/solventy) caused from a high temperature. If the probe is at the top of the FV, with a glass shelf going right across at the bottom, this seems quite likely to me.

It's good practice to build a thicker wooden stand/shelf that allows better airflow around the sides and in my view have the probe insulated about half way up, on the outside of the FV.

[danwlx]

Thanks for the responses guys.

The taste is distinctively of apples at this point which is why I'm assuming its Acetaldehyde. I'm brewing again this weekend and will try moving the heater alongside the FV, this should allow better airflow. Would I be wise to wrap the wall of the FV near the heater with foil to try and prevent hot-spots?

[Jocky]

I think you've nailed the main possible culprits here - this is probably yeast stress caused, by either under pitching or under aeration. Heating issues could also cause it - it might be worth getting a cheap hi/lo greenhouse thermometer to monitor ambient temperature.

Did you ensure you had enough healthy yeast to pitch? After a couple of dead packets of dried yeast (well within date) I try and start all my yeast now.

[danwlx]

I only pitched one packet of the NBS Yeast 2, this was from a MM kit and it was rehydrated but didn't show much life before being pitched so i'm wondering if the already underpitched yeast was stressed further by being overheated on the glass shelf. I will be going back to a liquid yeast with starter and the immersion heater in bucket for the next brew until I can sort out a wooden stand for my fermentation fridge.

On that subject, I have no tools or diy skills! Does anyone have any pointers / tips to making a stand. I have an annoying design of fridge which has a half plastic low shelf which then turns into a glass shelf as it reaches the door, I think this makes a stand a little tricker?

[Padalac]

Stupid question, but does that shelf definitely not come out?

[danwlx]

Given my lack of DIY skill it is not a silly question! Unfortunately not, the plastic part is moulded into the back of the fridge, it extends down so forms a hump at the bottom of the fridge, i presume it houses gubbins.

[MTW]

I only pitched one packet of the NBS Yeast 2, this was from a MM kit and it was rehydrated but didn't show much life before being pitched so i'm wondering if the already underpitched yeast was stressed further by being overheated on the glass shelf. I will be going back to a liquid yeast with starter and the immersion heater in bucket for the next brew until I can sort out a wooden stand for my fermentation fridge.

On that subject, I have no tools or diy skills! Does anyone have any pointers / tips to making a stand. I have an annoying design of fridge which has a half plastic low shelf which then turns into a glass shelf as it reaches the door, I think this makes a stand a little tricker?

Most fridges have that arrangement, with an intrusion from the compressor housing taking up a portion at the bottom, part glass shelf to the front.

Here's mine. I just used a piece of wood that reached the full depth backwards (but not right across - you want the airflow) and screwed two legs across the side-front edges, with a strut between them for strength. That way, the weight is distribuited between the compressor housing and the two legs into the floor of the fridge. Heater goes crossways behind the legs (which I mounted on a loose board). Check the legs leave clearance for that.