[Ben A]

Hello.

I brewed a Marzen about a month ago, and the airlock just started bubbling again after 3 weeks of inactivity. I’ve been brewing for about four years now, but I’ve never had this happen before. My first thought is an infection. But the aroma is clean and there’s relatively vigorous bubbling, so it’s hard to be sure.

Smelling it, I’m getting raw dough / yeast, a little bit of toasted malt, and some fruit. The smell is about the same as it was during primary.

I pitched about 8 oz of 34/70 slurry I saved from a Czech Pils (about 2 months old). Primary started strong after ~36 hours. There was almost no airlock activity about 48 hours after primary started. The gravity was at 1.016 after two weeks in primary at around 70-72 F. After I got that reading I swirled the fermentor to resuspend the yeast twice in two days. I didn’t see much activity after that. Now, two weeks later, it’s fermenting again.

If anyone has any thoughts on why this is happening, or has experienced this before, I’d be grateful to hear.

Thanks,
Ben A.

P.S. - I’ve included the recipe below

Brew Method: All Grain - Style Name: Märzen - Boil Time: 60 min - Batch Size: 20.8 liters (fermentor volume) - Boil Size: 24.6 liters - Boil Gravity: 1.050 - Efficiency: 82% (brew house) - Hop Utilization Multiplier: 0.8

STATS:
Actual Original Gravity: 1.059
Target Final Gravity: 1.011
ABV (standard): 6.4%
IBU (tinseth): 22.27
SRM (morey): 9.49
Calculated Mash pH: 5.18

FERMENTABLES:
1.7 kg - Stone Path Pilsner (36.2%)
1.25 kg - Briess Bonlander Munich (26.6%)
1.25 kg - Stone Path Nor’East Munich (26.6%)
0.5 kg - Briess Victory (10.6%)

HOPS:
50 g - Tettnanger, Type: Pellet, AA: 3.9, Use: First Wort, IBU: 20.89
6 g - Tettnanger, Type: Pellet, AA: 3.9, Use: Boil for 20 min, IBU: 1.38

MASH GUIDELINES:
1) Infusion, Temp: 68 C, Time: 60 min, Amount: 28.51 L

OTHER INGREDIENTS:
7 g - Gypsum, Time: 0 min, Type: Water Agt, Use: Mash
5 ml - Lactic acid, Time: 0 min, Type: Water Agt, Use: Mash

YEAST:
Fermentis / Safale - Saflager - German Lager Yeast W-34/70

TARGET WATER PROFILE:
Ca2: 94.1 Mg2: 8 Na: 40 Cl: 176 SO4: 184 HCO3: 0.7

[neuse]

Looks to me like a yeast health issue. It stalled at 1.016 (significantly higher than expected), and later restarted.

[denny]

Are you certain it's fermentation? Have you checked the gravity?

[Ben A]

Looks to me like a yeast health issue. It stalled at 1.016 (significantly higher than expected), and later restarted.

That explanation certainly makes sense. Though I haven't heard about many stuck fermentations restarting spontaneously (at least this actively, around 5 seconds per bubble). It has me thinking something something else is going on, but I might be overthinking it.

[Ben A]

Are you certain it's fermentation? Have you checked the gravity?

Just took a gravity reading, it's down to 1.013. I'm thinking it's fermentation for a couple other reasons too.
- There is still consistent airlock activity after four hours, around 5 seconds per bubble
- The ambient temp in my basement has been dropping (down to 65 from ~70), so I don't think it's offgassing due to temperature.
      - The airlock was actually sucking in sanitizer about a week ago
- When I took the gravity reading, there was a small layer of foam on top of the beer and I could see bubbles rising to the surface.

[brewthru]

If yeast, then what caused the stall? Too low temp?

If not yeast, then probably an infection.