My research indicates that chestnuts are actually a favored malt alternative for gluten-free brewing; apparently, it's one of the closest "bases" that celiacs and others who just want beer sans-gluten have found to be similar to barley malt. Unfortunately, the great preponderance of gluten-free recipes based on chestnuts stands at odds to the dearth of recipes that use chestnuts more like an adjunct. Most threads and such I found said that because the flavor characteristics were so similar, that it was almost pointless to use chestnuts in a barley-based beer. Well, I'm not satisfied with that, and since I'm getting about 50 pounds of them for free (!!!) I have room to experiment.
The threads about GF beers using chestnuts call for long mashes with ground up chestnuts (they are very carbohydrate rich and relatively lipid poor compared to most other tree nuts), but they use added enzymes since there is no malt to make the conversion happen. Obviously, that won't be an issue with pale malt as the base. With all the starches, I'm going to boil the nuts in shell (standard practice) to gelatinize the starches. But, I'm shooting for a darker beer (porter), so I want to bring some caramelization to the party. That means roasting them... on an open fire or elsewhere.
Since I'm going to do this as a 2.5 gallon BIAB test batch, I had the brilliant (my own perception) idea of boiling the chestnuts in the strike water for 15 minutes. That way, I have a nice sweet chestnut wort to begin with (I think the potential gravity of chestnuts is fairly low, seeing evidence of 1016-1020 PPG referenced). When the chestnuts are done boiling, I'll set the mash water aside and put the chestnuts in the oven at about 400dF for 20-25 minutes (still in shell, at this point). This is pretty much how chestnuts are roasted for general consumption. When that step is complete, I'll shell the chestnuts, throw them in the food processor to coarsely chop them (I may reserve the roasted shells to see if there is any additional nutty flavor that comes from them), and then mix them with the malt in the reserved mash water. By this point, I'm guessing that the strike water will have come down to pretty close the perfect temp for a full bodied mash. From there, I'll do the mini-BIAB mash, sparge, and boil.
Here's my recipe:
Recipe: Chestnut Porter
Style: Brown Porter
Recipe Specifications
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Boil Size: 3.71 gal
Post Boil Volume: 2.96 gal
Batch Size (fermenter): 2.60 gal
Bottling Volume: 2.50 gal
Estimated OG: 1.052 SG
Estimated Color: 27.5 SRM
Estimated IBU: 22.8 IBUs
Brewhouse Efficiency: 75.00 %
Est Mash Efficiency: 83.3 %
Boil Time: 60 Minutes
Ingredients:
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Amt Name Type # %/IBU
4 lbs Pale Malt (2 Row) US (2.0 SRM) Grain 1 74.4 %
3.0 oz Black (Patent) Malt (500.0 SRM) Grain 2 3.5 %
3.0 oz Carafa II (412.0 SRM) Grain 3 3.5 %
1 lbs Chestnuts (20.0 SRM) Sugar 4 18.6 %
0.75 oz Goldings, East Kent [5.00 %] - Boil 45.0 Hop 5 22.8 IBUs
0.50 Items Whirlfloc Tablet (Boil 15.0 mins) Fining 6 -
0.25 oz Goldings, East Kent [5.00 %] - Aroma Ste Hop 7 0.0 IBUs
1.0 pkg SafAle English Ale (DCL/Fermentis #S-04) Yeast 8 -
Mash Schedule: BIAB, Full Body, Batch Sparge
Total Grain Weight: 5 lbs 6.0 oz
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Name Description Step Temperat Step Time
Mash In Add 5.47 qt of water at 170.7 F 156.0 F 45 min
Mash Out Add 9.14 qt of water at 176.3 F 168.0 F 15 min
Sparge: Fly sparge with 0.59 gal water at 168.0 F
(Forget the part about fly sparging; I can't get BS dialed in to fly sparge with 0 gallons, and the BIAB profiles or batch sparge steps calculate out the way I want to do my BIABs. That amount just goes into the mash out water.)
I'm skipping caramel/crystal malts and other body builders as I'm mashing high, and the chestnuts are very sweet already, so I'd like this character to come through. I might try to get something like Carapils before I brew this, though. Just a small amount of dark malts to add a touch of roast (and this is where I thought I might add some of the ground up roasted shells too), with some scant hopping--nothing to challenge the chestnut flavor too much.
Any thoughts? No matter what, I'll document this well, as there isn't a lot of other information out there that I have found.