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In May I brewed the following beer:

  • 81% Pale 2 row malt
  • 16% Brown malt
  • 3% Black malt

Single step mash at 73C.

With 290g of hops for a total of 103 IBUs.

The OG was 1.077 and it went into primary fermentation at around 18C on 9th May. With an old vial (around 1 year after the best used date) of WLP007 Dry English Ale (I made 2x 1.5l starters for it).

So on the 16th May i checked again and it dropped to 1.036, waited and on the 5th June it still was at 1.036 (figured the fermentation was finished?) so I racked into the secondary and added 50g of Burbon soaked oak chips.

On the 27th of June I racked it of the oak chips as the beer already had a heavy tanninic/woody/unpleasant note.

As I didn't have any space in the cellar I moved it into the flat and stood there (no bottles for filling) at around 23C.

And then the fermentation started again. The airlock got activity and by the 9th of September dropped down to 1.009.

Now 9th of October it went down to 1.006 and activity is still present.

So I was wondering what happened? It is a very attenuative yeast but down to 1.004 should not happen especially with the high mash temperature.

So possibly contamination with a wild yeast? The beer is at the moment quite hash, but at that IBU and alcohol content with not much sugar left it is no wonder.

I thought about waiting for the residual fermentation to stop and then adding lactose to get some sweetness back in?

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    Maybe not yeast at all. There are other microorganisms able to eat sugars that are not fermentable for yeast. Sadly, they usually don't produce alcohol as far as I know. 73C produces a lot of non-fermentables, right? So it leaves a lot for wild stuff.
    – Mołot
    Oct 10, 2015 at 11:39
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    I think Molot is saying 'yes', and I think he's right (and should make it an answer). At your mash temperature only alpha-amylase would have been working (after the first couple minutes), so the 1.036 probably was as far the WLP007 could go. You might be able to tell whether it's yeast or bacteria by the taste; it seems that nearly any kind of yeast will give you something beer-like, given enough time.
    – Pepi
    Oct 11, 2015 at 6:20
  • Thanks for the replies. The taste is fine in my opinion. A bit harsh as not a lot of sugar is left but not all too unpleasant. There is a flavour I cannot really identify, if I take Palmers list (howtobrew.com/section4/chapter21-2.html) the closes would be medicinal/phenolic.
    – Icewind
    Oct 12, 2015 at 11:41
  • @Pepi First, if you would use @ before my nick, I would know you mentioned me... Second, I'm really reluctant to put wild guesses as answers. I posted it at all just to broaden op's vision on this matter.
    – Mołot
    Oct 15, 2015 at 10:59

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I would guess that it is has become contaminated, but the easiest way to determine would be to taste & smell the beer. If you get sourness or any off-flavours (vomit, rotten vegetables, butterscotch, burnt plastic) then you have contamination(yeast or bacteria).

If the beer still tastes fine, then it may be that your yeast is just exceptionally hard working. The higher temps may be what is waking them up.

Lactose might help, but I would be wondering if you are not throwing money at a bad beer. Pour a glass and see if adding lactose can save it. If it does taste better, then all is good (please let us know). Otherwise, dump or still the beer and brew it again.

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    Thanks for the reply. The taste I had of the beer is quite okey right now. There is definitely something I don't know, but I would not describe it as one of the things you listed. I think it probably is due to the oak chips. And I tried it with added sugar, it improved the beer (balancing it).
    – Icewind
    Oct 12, 2015 at 11:37
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    To help with flavour identification, try and get a BJCP judge that is in your area and ask them to help you identify the flavour. They might also help you with finding out why the beer did a lazarus on you. :)
    – Atron Seige
    Oct 12, 2015 at 11:40
  • Well the problem is I don't really know any people that are into homebrewing where I live (Vienna/Austria). Maybe I'll ask the guy at the beer store where I sometimes buy a beer his opinion. But I guess that would make for an awkward conversation. :D
    – Icewind
    Oct 12, 2015 at 11:50
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    You'd be amazed! Most home brew shops that I know of, the shop owner is used to getting questions like "does this taste funny to you?". :) I had a look and there are no BJCP judges in your area. Sorry. There are judges in Germany, Italy, Poland, Holland, Russia, Sweden and the UK. If any of those sound close by (I am too lazy to look at the map) then let me know and I will ask them if they are willing to assist you.
    – Atron Seige
    Oct 12, 2015 at 12:15
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    Something else that you can try: If you can make a friend with someone who works at a big brewery. They have sensory specialists that you can maybe ask for help. Or; make friends with people at a local micro brewery that has been brewing for a while. Ask the brewer (or whoever does their quality control) if they are willing to help you. They are usually very friendly and happy to taste a few beers.
    – Atron Seige
    Oct 12, 2015 at 14:26

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