Imperial fruit beer gone lactic on accident?

[tonymark]

I brewed a Imperial stout base for an raspberry imperial stout back on March 13 (OG 1.093 mash 154F). I pitched on a 1968 yeast cake and it was down to 1.032 in 48 hours at 64 F (insane yeast!). Down to 1.023 2 days later. Dropped down to 1.021 over the next week and sat there for 10 weeks.

At 10 weeks checked and still at 1.021. Added 6 lbs of thawed frozen raspberries to 4 gallons. Fermentation was pretty heavy for 2 weeks (sitting at air temp 70-80 F). Airlog is still bubbling at 5 weeks from fruit addition. Checked and gravity is 1.013.

Even taking into consideration of a .0006 (calculated) increase in gravity from fruit that is around 85% apparent attenuation. I don't think 1968 is capable of that at the top end of its alcohol range.

The gravity sample tastes pretty good and it is pretty darn tart. Does it look like beer has gone lactic? I am really ready to bottle this batch. May have to wait another 5 week and see what happens to gravity.

I still have the other half. Maybe I will puree and flash pasteurize the berries for that half. I might even consider a can of stuff from Oregon Fruit.

Any thoughts?

 

[WayFrae]

I have never added raspberries but I wouldn't be surprised if the tartness is just from the raspberries since all the sugar fermented out. If it was a lacto infection you would see a pellicle forming on the surface of the beer.

 

[ldbf]

6 pounds for 4 gallons? That seems like a ton.

 

[tonymark]

It's a lot of berries. The last time I made this beer was 1994 and it was the same ratio of berries to beer. I was so good, but it finished at 1.026 and stayed there, so there was a good bit of sweetness to balance out the tartness of the berries.

As for the pellicle, still lots of bubbles holding faded berry fragments on top of the beer. The berry addition also caused it to be an extremely full carboy. No real head space but neck and it is full of berries. Maybe I will transfer it into another carboy to remove the berries and gain some headspace. How long does a pellicle take to form?

I am just floored that it could drop that low with 1968 without some bacteria helping it along.

 

[tonymark]

I guess I will get no expert opinion on this topic. Anyone want to recommend a better homebrewer group/forum/board/news group?

 

[MindenMan]

tonymark, me thinks thou doest protest too much. Are you F-ing serious? Okay, let me insult everyone on this forum, and then ask for their help.
With that kind of attitude, go elsewhere and stay there. It's only been three days, corn hole. Get a clue, get a grip, and drive elsewhere since it appears we can only steer you wrong, or not at all. BYE!

 

[WayFrae]

I have never used 1968 but I just brewed a 1.087 batch with 1272 and it finished at 1.014. Maybe you mashed lower than you thought? Have you calibrated your thermometer? Im not sure how long the pellicle would take to form but I am pretty sure it eats through the remaining sugars much more slowly than you are experiencing.

 

[tonymark]

Maybe you mashed lower than you thought? Have you calibrated your thermometer? Im not sure how long the pellicle would take to form but I am pretty sure it eats through the remaining sugars much more slowly than you are experiencing.

Thermometer is new glass lab type. I made sure i was accurate when I first bought it. Thing is, except for wheats, belgians and stuff I want to finish drier, I brew almost every ale with 1968. Even mashing at 148 F, it can't usually take a 1.058 beer below 1.012. Maybe it is the warm temperature, never really brewed with it at 79 F.