Imperial pumpkin (low original gravity)

[Odin66]

So no **** there I was, mashing my pumpkin beer. The anticipated og was 1.103 with my actual og post boil (complete and almost on point 5 gallons) being 1.064. Now I monitored the mash temp (152) the entire time (60 min) and it was spot on. In the mash, I used three large cans of Libby's pumpkin purée (baked of course). I sloshed it around just like the grains. Does anybody have an idea as to why the og ended up being so low? Every other beer I have made turns out fine (second time with pumpkin it's done this). For such a large gap in OG, I feel as though there is an extremely well hidden obvious reason for this. Thanks in advance!

 

[LLBeanJ]

What would your expected OG be if you backed the pumpkin out of the recipe? The first pumpkin beer I brewed, I was expecting a fair amount of sugars to come from the pumpkin and essentially got none. Now I mark my pumpkin as "not fermentable" or add it as a flavor addition and my gravity numbers are much closer.

 

[Odin66]

I didn't factor pumpkin in at all as far as fermentables. Only the grains.

 

[LLBeanJ]

Okay, then we'll probably need to see your recipe.

 

[Odin66]

16 lb 2 row
2 lb crystal 20
1 lb cara amber
3 large cans Libby's pumpkin puree

 

[LLBeanJ]

Grain bill looks fine. Is it safe to assume that your crush was as per usual?

What was your mash thickness? Thick, as in standard mashing, or thin, as in BIAB?

How long of a boil? A lot of the time with very big beers like this, it will be necessary to increase the boil to 90 min or even 2 hours (or even longer!). The reason being, with a normal sparge to reach the pre-boil volume for the usual 60 minute boil, a lot of the sugars are still left behind in the grains, especially if mashing on the thick side. Sparging more will get more of those sugars into your kettle, but the result is a higher pre-boil volume that will take more time to boil down to final volume. Add to that what must be around 90 oz. of pumpkin gumming up the works, I wouldn't be surprised that you had some efficiency issues.

Now, if you come back and tell me your crush was practically flour, you mashed really thin, and sparged for a 3 hour boil, I'm afraid I'm going to be out of ideas.

 

[benzesp]

Had a similar issue when doing an Imperial Stout. Missed my og by 20 points. I had so much stuffed in my mash tun I don't think I mixed it with my strike water thoroughly. Maybe the pumpkin is screwing with your first runnings and sparing. Why not add it in the boil kettle in a bag instead?

 

[Odin66]

Mash was thin (~1.75 qt/g if I had to guess), and the boil was 60 min. I started with 6.5 gallons and ended with almost exactly 5. I think you may be right about sparging more though (since mash was thin I only poured three 2 quart pitchers on it). I was going to but decided not to figuring I was good to go since the wort coming out was virtually clear. I believe the pumpkin purée has something to do with it however. And I put it in the mash after roasting it in order to get more of the pumpkin flavor out and not have to deal with all of the floaters and crud from it later. Surprisingly, no stuck sparge though! It was nice the entire 75 min it was going!

 

[Odin66]

The crush was whatever homebrew.org does. Haha