Stout and bananas.

I decided to remake the chocolate stout, but without the chocolate. I’m really enjoying stouts and porters this winter, and although I’ve probably left it a bit too late – it’ll be well into spring by the time this one is ready to drink – it doesn’t hurt to have a couple of crates of the black stuff in stock.

I decided to add a bunch of extra DME to this one, in the hope of pushing the ABV into the 7-8 percent territory which will permit me to call it an imperial stout. We can but try.

So, in addition to the 2 tins of stout extract and the 1KG of stout enhancer, I’ve chucked in 500g of DME and some lactose. I’ve used the same SafeAle 04 as before.

All went according to plan, and the SG was 1.08 so things were looking decidedly positive. The fermenter was set at 18 deg, a nice gentle temperature, and fermentation started less than 24hrs after I pitched the yeast. This was some sort of record. After 48hrs, it was going mental, a bubble passing through the airlock every 3 or 4 seconds. This continued for another 24hrs, and then when I went down to check on it on the morning of day 3, I was in for a surprise.

I opened the refrigerator door and was hit by a very strong and unusual aroma. It took me a while to place it, because although it is a common and easily identifiable smell, this was not the situation in which I would expect to find it. Bananas. Really fucking bananas. I would imagine that whatever is making this smell is the same thing they use to make banana flavours in sweets and stuff. It smells like banana muffins when they first come out of the oven.

This is not an intended aroma, this is most definitely an off-flavour, so I quickly consult the interwebs for advice and it turns up the following possibilities:

  1. Too warm fermentation
  2. Insufficiently aerated wort
  3. Infection

I can immediately discount 1. as my STC1000 was set at 18 degrees, which is just about the perfect temperature for a stout. Insufficient aeration is a distinct possibility, because to be honest I never do more than pour the wort into the fermenter from a few feet up so it sloshes about a bit. It’s never been a problem before though. I discount this possibility a few days later, as fermentation is still going on. Surely lack of oxygen would have killed the yeast before all the nourishment was gone out of the wort?

The most likely candidate, I surmise, is infection. I noticed that the foam on the top of the wort had reached up as far as the lid in the first couple of days of ferocious fermentation – I sanitise the inside of the lid, but not as fastidiously as the fermenter itself. It could also have been the wort chiller, which has been hanging in the basement through some fairly dirty and dusty renovations. It was bagged, and I did give it a quick clean and spray with StarSan but perhaps I’m getting a bit lax these days.

All I can really do is try my hardest to eliminate these possibilities next time.

After 2 weeks when fermentation is all done, the stout has a slight sweet taste, but it’s thankfully not bananas. I can’t decide if the sweetness is solely due to the lactose or not, but it’s certainly not the ‘cloying’ sweetness that one reads about. Definitely worth bottling though, so there are now 2 dozen conditioning at 18 deg in the fridge.


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