I seem to have encountered a couple of problems recently with off flavours. I am struggling to pin down the causes.
First, Brew 88, seems to have oxidised really quickly. It was the first time I was had used Toasted Oat malt from Crisp and 750g in a single batch might have had an effect. Overall, I had reduced the total amount of hop content – to ensure that it didn’t overpower the toasted oat flavour. I think overall this was a bad choice of recipe on my behalf – the toasted oat flavour did come through, but it didn’t work well with a Pale Ale recipe.
Anyway, a few weeks after bottling and this brew was starting to look a little grey and starting to taste like cardboard – no off tastes, just no taste at all and a shadow of the beer when it was first bottled. So 20 weeks after being bottled, what was left of this batch went down the drain!
The next problem.
Batch 93 (this one went straight into a keg) starting showing signs of an off taste a 1 or 2 after being kegged – a sort of metallic honey flavour. It was brewed from an all grain kit, so I put it down to an odd choice of malt or hops. No drama, I thought. I cleaned and sanitised the keg and the lines. Then I put batch 100 into the same keg. This was an IPA recipe of my own and I knew exactly what was in it. 2 weeks after kegging, the same off taste (metallic honey) started to appear in the beer.
Strange. Batch 97 is in another keg and is still going strong – with no off taste.
So what has gone wrong with batch 100?
- Oxidation – I can’t believe that this is the issue as the transfer from the FV to the keg was via a closed system. However, I do think this could be an issue when bottling really hoppy brews. This might explain brew 88.
- Contamination – this too seems unlikely since everything was thoroughly cleaned and sanitised after the last batch. I will be even more thorough next time.
- Over pitched yeast – both batch 93 and 100 used Fermentis US-05. But batch 93 had a packet as it was supplied with the kit. Batch 100 had my repackaged 20g of US-05. I can’t believe that this is the issue.
- Too much DWB in the mash water – I am following the instructions I got from water tests and am adding 24g of DWB to a 25L batch. I have double checked this and it is correct.
- Yeast by-products – Acetaldehyde and diacetyl are produced as a by-product of the fermentation process. While these can cause off flavours, they are removed by the yeast if the fermentation process is allowed to complete. Stressing the year during fermentation will increase the amount of these chemicals produced. Cutting the fermentation process short, it reduce the opportunity for the yeast to remove these chemicals from the wort.
I think this last reason is the most plausible in my case. I have checked my records and the fermentation seems to have completed in 7-9 days. On refelction, I could be cutting this a bit short. I wonder what would happen if I increased this duration as well as increasing the FV temperature (to encourage the yeast to remove these components) at the end of the cycle?
Fortunately, brew 101 is just coming to the end of it’s fermentation cycle. So here is what I am going to do:
- Make sure that the keg and pipelines are all thoroughly clean;
- I am going to increase the FV temperature to 23C for 2-3 days from the end of fermentation just to make sure that all the acetaldehyde and diacetyl has been processed out of the beer;
- Transfer from the FV to the keg using a closed system. Again making sure that all the pipework is thoroughly clean.
Let’s see what happens!