Yeast Coming out of fermentation or contamination?

General Pointers
All of the questions concern Secondary Fermentation
I've been careful with transfer and sterilisation, using fermenters with taps & no syphoning.
This has happened when brewing in different locations around my area (Same pattern), so if its airborne its in the air around Manchester UK, but thats a bit wierd (the industrial smog went a long long time ago)...I dont think it is airborne bacteria nevertheless.
I added clearing agents - Gelatin last time, and Isinglass this time. both sterilised with v.hot water.

The Pattern
After adding to secondary, it takes 2-3 days for the pellicle to form, it looks like a contamination. But I've bottled following this.

Smells a bit sweet in the secondary phase, making me thing 'green beer'. Because of this I've thrown some out, seemingly a waste.

After bottling and carbonation, the beers have turned out just right, some have been given top scores by knowledgable drinkers and a local artisan beer store owner.

I'm keen to know what this is, and why it is happening.

If it is yeast leaving suspension, why do the flavours change between, the smells, and what happens to this pellicle.

If, as some on this forum have said, its Acetobacter, why does the beer turn out crisp and fizzy after bottling?

Pictures below.

Batch 1 (Pale Ale)
Pellicle has formed and seems to be getting more complex / network like. Not collapsed yet.



Batch 2 (Dunkel) (Same process same timing)
Before I left my flat a couple of days ago it had a pellicle like the other photo, now it has collapsed / dissappeared. This beer now tastes nicer after this has happened. It also seems to have regained a level of carbonation almost tasting on its way to maturity.




Long winded question, but I'm interested in the science behind this. Its also a mystery why nobody else asks about this.

Thoughts?

"regular" yeast does not form a pellicle so you have a wild yeast getting into your beer at some point. that it tastes good is not that surprising, wild yeast do not always have a bad taste. any beer can be crisp and fizzy after bottling regardless the yeast used to ferment it but if it was acetobacter it would probably have a pretty strong taste of vinegar. if you have a wild yeast that tastes good i would wash it and keep using it.

Cheers - the only question I have then, is if you know any resources for washing and storing wild yeast strains?

Pellicle is a scum mold--familiar to makers of pickles and other fermented products. It requires oxygen to grow and can be prevented by not disturbing the CO2 layer after the fermentation starts (and after it stops).

Tiltie, does that mean that this is probably happening because I'm transferring to a secondary which causes exposure to O2, and losing CO2 in the process?

Most of my experience with scum mold is with sauerkraut making where it occurs a the drop of a hat and is regarded by many as normal. With beer, it seems to be rarer. (I’ve never seen it except when pictures appear in this forum.)
Re: secondary, I’m a strictly “primary and bottle” person but my guess is that the act of transferring to the secondary introduces a bit of 02 that produces some more yeast activity and regeneration of the CO2 layer and that its subsequent trips in and out (e.g. gravity readings) that are more risky. This would be both from the aspect of CO2 loss and mold spore introduction.

Ummmm, don't secondary?

PartisanBeers said:

Cheers - the only question I have then, is if you know any resources for washing and storing wild yeast strains?

Click to expand...

there is a sticky in the yeast and fermentation section on yeast washing but i'll tell you how i do it.

boil a quantity of water (depends on the size of the batch, i boil 1 gallon for a 5 gallon batch) along with come glass canning jars and their lids. let cool overnight.

after racking the beer off of the yeast pour the cooled/sterile water into the fermentor and swirls the whole thing around.

let it sit for 20 min and you'll see a lot of the trub/hop bits will settle out pretty fast leaving a layer of milky looking water.

pour this water into your jars being careful not to pour the trub in and cap them. some people pour the liquid into a smaller container and let it settle out more before pouring into the canning jars but i don't bother.

(you could even skip the washing, pour the the trub and all into a sterile jar and that would keep for weeks if not months, i've done that too.)

i keep everything very clean while doing this even though it is a wild yeast because i want only the yeast i fermented with and not some new strain that might not taste as good.

good luck!