Is Fermentation Beginning Again?

[syke0021]

My Tart Cherry Imperial Stout has recently started fermenting again after several months. After putting a lot of love and preventative care into it, I'm worried that I may have a problem. I'll provide as much information as I can in search of an answer or possible solution:

Recipe:

OG: 1.084

11.00 lbs Maris Otter
4.50 lbs MaltEurop Pale Ale Malt
1.00 lbs English Roasted Barley
0.75 lbs Black Malt
0.75 lbs Fawcett Pale Chocolate Malt
0.75 lbs Weyermann CaraWheat

60 min: 1.00 oz Centennial Pellet Hops (9.9% AA)
20 min: 0.50 oz Simcoe Pellet Hops (12.9% AA)
15 min: 1.00 oz Amarillo Pellets Hops (7.4%AA)
10 min: 1 Wirlfloc Tablet
5 min: 1.00 oz Centennial Pellet Hops (9.9% AA)
0.50 oz Simcoe Pellet Hops (12.9% AA)

Aerated with 90 seconds of oxygen
2L Starter w/2 Vials of White Labs WPL007 English Dry Ale Pitched

Fermatation:

Primary Fermentation for 16 days (68 degrees with temperature controlled)

FG: 1.025
Attenuation: 70.2%

Racked onto 10 lbs of Tart Cherries. Tart cherries were frozen for 1 month after picking. They were soaked in 16oz of Woodford Reserve for a few hours as they came up to room temperature.

Secondary fermentation for 10 weeks (on the cherries)

Fermentation renewed after a few days. Signs of fermentation included airlock bubbling, some visible activity in glass carboy, and very thin krausen atop the cherries. The airlock activity and other signs all ceased after two weeks. The length of time on fruit was intentional to allow the tartness of the cherries to mellow and better pair with the Imperial Stout.

Gravity was recorded at 1.017 at this point. The change in gravity was expected with the addition of fruit and booze.

Tertiary Fermentation underway (off cherries)

It's been about 5 days and I'm seeing airlock activity again. This actually started up a few days before racking off the cherries. It has coincided with a slight drop in temperature in my fermentation room from 70 degrees to 67 degrees as the seasons change.

Help!

I'm concerned that any fermentation taking place at this point may be a sign of either a bacterial infection or wild yeast. I feel like I've taken all the steps I can to use fresh cherries and avoid such an infection, but realize nothing is full proof. However, I'm curious if there could be another possible explanation or solution.

Any advice or tips would be greatly appreciated.

 

[RPh_Guy]

And the current SG is .... ?

 

[syke0021]

And the current SG is .... ?

I honestly hadn't checked until now! I use a lab grade hydrometer and try to avoid taking samples unless needed. I recorded it at 1.0165. When I'm between whole numbers, I usually round up. I can't recall if I did this or not 5 days ago. So, I'm either the same or have dropped a half point in that time.

FWIW, when tasting the sample, it's very difficult to separate any off flavors that could be due to infection from the tart cherry flavor. I like tart beers, and this has a major Surly Pentagram thing going for it, but I figured that others may like it better if the tartness mellowed out.

 

[RPh_Guy]

So, since s.g. presumably didn't change, it's not fermenting. Easy peasy!

If s.g. drops in the future, you'll know it is fermenting.


FYI ...
Microbes live inside fruit. Freezing does not kill them. Washing, soaking, or dipping whole fruit in alcohol or sanitizer does not kill them.
You need to either heat pasteurize or puree/juice and sulfite to be sure you aren't introducing wild microbes.

Transferring a beer 3-4 times certainly also increases risk of contamination and oxidation. Something to think about for the next batch!

Sounds tasty, good luck!
Cheers