Solvent off flavours in last 3 beers

[Mya]

My last 3 beers (IPA, weissbier, blonde ale) have all had solvent off flavours (my first few didn't).

I haven't changed any of my equipment before and now so unsure why this would start now.

I ferment in a 30L fermenting barrel like the type you buy from a HBS. I use a 200L fridge with an STC1000 controlling the fridge and a 17W herb heating mat next to the fermenter. The first two beers had the probe stuck to the outside of the fermenter with some insulation material between the probe and the air (as did my prior beers without any problem and is widely used without problem), the latest I have a thermowell protruding into the liquid about 50mm (not ideal but better than the outside I'd assume).

The first two beers used one barrel fermenter, I changed fermenter for the third beer so it was an entirely different 30L barrel fermenter (only used for 1 batch prior and not used for the batches with solvent off flavours).

I ferment at normally 19 then after fermentation stops I raise to 20 for a day and 21 for a day and then rest for a couple days. Then I remove the airlock, put sterilised foil over the bung and cold crash/gelatine fine for 2 days then keg.

I check the temp reading on the STC1000 during fermentation and it's always on setpoint.

I checked the probe vs a mercury thermometer and the STC1000 was reading the correct temperature. The only thing of note is that the temp reading on the STC1000 jumps around a lot, like +/- 0.5 degrees (eg between 18.5 and 19.5 if on 19 setpoint), this can't be ideal but I've read you need quite high ferment temperatures for there to be an issue for us05/danstar etc, eg over 21.

I've seen note of using non food grade pvc/vinyl tubing, the tubing I use for transfers is the "food grade" stuff from bunnings/mitre 10 (it has "drinking water" written on it).

I cool to ~25 degC in the kettle (I have a Guten) and then drain to the fermenter and let the fridge cool it down to ~18 before pitching.

The IPA used us05 which I rehydrated, the weissbier used WLP300 which I used a starter for (although there was a long lag time before airlock activity), the blonde ale was danstar nottingham which I rehydrated and it was fermenting within 12 hours.

I use campden tablets at the recommended rate to remove chlorine (we have very low levels of chloramine).

Anyone have any idea what I should check?

 

[MHB]

When you chose to have "Solvent" as your problem you picked a doozy. There are so many possible answers that it could easily be a stick a pin in the phone book.
Having said that, yeast, wild yeast and bacterial contamination are among the most common answers.

For your reading pleasure Complete_Beer_Fault_Guide.pdf
Hit Ctrl F and search for Solvent, you will find heaps of hits and lots of information, worth seeing if anything looks like it makes sense.
Mark

 

[Mya]

My first research suggested it was likely a wild yeast/bacterial infection (so I've thought about this a lot already) but later research all suggested it was due to high fermentation temps.

Going through the causes:

- Yeast strain/underpitching/health: 3 different yeasts were used, both dry yeasts within use by date and were rehydrated, liquid yeast was made into a starter with good activity, should have good cell count. Also my latest blonde ale with danstar nottingham was active within 12 hours
- High temp fermentation: I believe I covered this
- Oxygen content of wort: I use one of those plastic aeration sprayers and have this spray into the fermenter, usually a fair amount of foam produced so presumably decent aeration
- Yeast mineral deficiency: I have always used yeast nutrients at the recommended level
- Wort gravity: not high, these were all in the 1.045 - 1.055 OG range, blonde ale was 1.046
- Trub: I cold crash and gelatine fine so I think I should have good trub separation, the trub is always a nice solid cake with very clear beer
- Aeration after fermentation starts: I don't touch it after fermentation starts

Wild yeast infection is the big one. Bacterial contamination doesn't appear to be listed.

I changed fermenters after my 2nd one, before the third, to try to rule out the mythic "scratches" in plastic that can harbour bacteria/wild yeast. I cleaned my second fermenter (which has been clean, dry and inactive for the past few months) twice with dishwash liquid, getting every nook and cranny (including the lid, thread, etc), removing the valve and putting a pipe cleaner through it, then I used a brand new batch of higher strength star san and soaked the bottom 20L with it (and periodically spraying the top section, threads and inner lid with star san from a bottle a few times). Minimised time between draining out the star san and adding in the wort.

During fermentation, Star san was in the airlock and I could see there was positive pressure inside the fermenter from the airlock water levels.

All transfer tubing is soaked in star san for ages before using. To cold crash I put sterilised foil over the bung.

Rehydration of the yeast uses previously boiled water, warmed up to 35 degC in a sterilised pyrex jug, stirred with a sterilised mercury thermometer.

After fermentation I took my old keg that had the bad beer in, drained it, stripped all the posts, o-rings, keg connectors etc, soaked everything in near boiling water. Put 4L of boiling water in the keg and shaked the ever loving shit out of it and the steel heated up to the point where it would burn me to touch it. Put the lid, PRV and lid o-ring in near boiling water too.

 

[MHB]

Free tip - don't be too quick to rule out things your sure you have covered. Go back over everything even the stuff your sure is right, even better get someone else to vet everything. Bit like playing patience, someone walks in and says put the red... an outside perspective can sometimes be helpful.

Second don't lock in on the term solvent, try some other related terms Acetone and Ethyl Acetate are often described as solventy and they aren't the only ones, some higher alcohols fall into the same bucket sometimes. Try to think outside the "Solvent" box a bit.

Take the heat plate out of the fridge and replace it with a small fan, a fan is a heater but it will prevent hot spots and improve the rate of heating/cooling. Check out the settings on your thermostat if they aren't set up properly they can be pretty erratic. Remember that a ferment is exothermic and a fridge is usually pretty well insulated, I have seen an allegedly well set up fridges push up over 35oC because the delay timer setting was way out of wack.

Sometimes we all get blind to a problem, good time to walk around the block and try to come at it fresh - luck.
Mark

 

[Tony121]

You need more than hot water to clean kegs and I wouldn’t use dishwashing liquid to clean any brewery gear.