A mysterious case of undercarbed gruit

[jonleven]

Hi All! I'm not exactly a beginner here, but new to the forums and this seemed the best place to ask this question.

I recently tried out two different batches of unhopped ale, one featuring just Yarrow, and another featuring Yarrow and Mugwort brewed 1 week apart. Both 1 gallon extract batches with S04 that fermented from around 1.055 to 1.015. I primed the Yarrow batch with 0.8oz of corn sugar and the Mugwort/Yarrow batch with 0.7oz of table sugar. I bottled both in a variety of bottles: 2 different swingtops and recycled traditionally capped bottles. I conditioned a bit low @62-70F for the first 2 weeks before moving to a more stable 70F after noticing carb issues.

Both batches have had either none or very little carbonation even after 4 weeks of conditioning, though interestingly my half full bottle with the dregs of the yarrow batch had low yet pleasant carbonation after 1 week.

One final note is that with a couple of the swing tops I put another half teaspoon of table sugar in and re-sealed afterward to see if that would improve anything (since I started to think maybe I went crazy and forgot to put the priming sugar in initially) but I popped one of those after 10 days @70F and nothing.

I'm starting to wonder if maybe the yarrow + age created some issue in which the yeast went dormant/died after primary but that seems unlikely to me. Did I maybe ruin things with the low-ish temperatures at first?
Am I missing anything else that might have been an issue, and anything I should try to salvage this?

Thank you!

 

[MikeCo]

I like To bottle condition above 70F to have the beer carbonate in 3 weeks. Try warming the bottles to 75 and give them some more time. Sometimes the yeast just need more time to carbonate bottles. Another thing to check is whether the bottles are air-tight. Maybe get new seals for the swing tops. You can add some fresh yeast to the bottles if nothing else works. Don’t add more priming sugar if you have initially put in the correct amount.

 

[jonleven]

Yes, I had considered that it might be the seal, but that would have to mean that both the swing tops and traditional caps had failed me. Possible, but unlikely.
I'm going to try a bottle I added some yeast to tomorrow and see how that goes. Hoping for some progress!

 

[Miraculix]

I got no idea what could be the reason but all my yarrow and mugwort asked carbonated just fine. But each harvest is different, so maybe these herbs were unusually potent in a yeast surpressing way? No idea tbh.

 

[Knox]

I'm starting to wonder if maybe the yarrow + age created some issue in which the yeast went dormant/died after primary but that seems unlikely to me.

I have made a yarrow gruit before and that did not happen to me. Mine bottle conditioned nicely within 2-3 weeks.

Did you dissolve the sugar before adding it? Sometimes sugar crystals takes awhile to dissolve in cooler environments.

How clear is your gruit? I have had issues with bottle conditioning when using S-04 if it flocculates hard.