[blair.streit]

So the good news is I kegged a rebrew of this beer last night. It's only 3 weeks old and uncarbonated, but the sample was smooth and did not show any of the off flavor discussed here.

The bad news is that I rebrewed this before I posted this question, so I changed several things with this batch (but not actually the Campden). That will make it harder to pin down exactly what happened. Relevant differences are as follows:

Good Bock

• 5.4 mash pH
• 1.2mL lactic added to sparge
• No mineral additions
• Hit strike temp of 155
• 81% conversion efficiency

"Chemically" Bock

• 5.25 mash pH
• 2.4mL lactic added (half each to mash and sparge)
• Minerals: 5g CaCl (mash), 2g CaSO4 (mash), 2g CaCO3 (kettle), 2g NaHCO3 (kettle)
• Initially overshot strike temp of 155 by 4 degrees, took 15 mins to cool from 159 to 155
• 78% conversion efficiency

Both batches were treated with half a Campden tablet in 11G of water. It's possible that the chloramine content was drastically different between March and now due to some shock treatment the water utility was doing.

However, it seems more likely that the low mash pH and/or the minerals were contributing to the off flavor. I'll update if any more data comes in, but otherwise it looks like I've learned all I can from this one.

[brewinhard]

Good to hear you are back on track. Nothing more frustrating than trying to isolate the cause of off-flavors in a beer made at home. So many variables and equipment in play that need to be looked at.

[zwiller]

Good to hear you are back on track. Nothing more frustrating than trying to isolate the cause of off-flavors in a beer made at home. So many variables and equipment in play that need to be looked at.

+1  RDWHAH

[blair.streit]

Stupid me. I think I know exactly what this was. Looking back at my logs I realized that I waited too long in between batches to do a straight repitch, so I made a "revival" starter to get the yeast going.

While my usual practice is to use distilled water for starters with DME, it appears that on this one I didn't. My notes don't mention anything about putting Campden into the starter water, so I probably just pulled it from the fridge filter.

Diluted into a 5G batch, the 2L of Chlorophenol laden starter wort was not as obvious as having the same issue with the full batch, but I'm almost certain that's where this off flavor is coming from.