I brewed a pumpkin ale on Wednesday. These spiced ales are popular this time of year, but I did one thing a little differently than most — I’m fermenting the beer inside of three giant pumpkins. 

The idea of fermenting a beer in a pumpkin is not original. A couple years ago, we profiled a guy (in Homebrew Nation) who did this. But, he used a regular Jack-O-Lantern sized pumpkin. I’m using  giant pumpkins that I grew myself. As such, I was able to fit 5 gallons (19L) of wort in a single pumpkin. The remaining 5 gallons (19 L) was split between two smaller pumpkins. 

Did somebody say, “Chris, I’m fascinated. Please tell more about growing giant pumpkins?” I know you’re saying, “no” — and I additionally see people who know me waving their hands and making that “cut him off” gesture — but I’m hearing “yes,” so here’s a quick introduction to growing huge mutant squash: 

Giant pumpkins are large, orange squash from the species Cucurbita maxima. (“Regular” pumpkins, such as almost all Jack-O-Lanterns, come from Cucurbita pepo.) They were bred from Hubbard squash and a Japanese winter squash called kabocha. In 1903, some guy named William Warnock grew a 403-lb. (183-kg) squash of this variety. (In contrast, a big Jack-O-Lantern type will weigh around 20 bs./9.1 kg) That record held until 1976, when Bob Ford grew a 451-lb. (205-kg) pumpkin. Since then, using a pumpkin variety bred by Howard Dill (Dill’s Atlantic Giant), the world record has been broken almost every growing season. In 2009, a young woman named Christy Harp grew a 1,725-lb. Atlantic Giant. Growing your own giant pumpkins basically involves planting the seed of a giant pumpkin variety — and these include Dill’s Atlantic Giant, Prizewinner and Big Max — in rich, well-drained soil, keeping the young vine protected from squash vine borers (insect pests that feed on the plant) and feeding the adult vine with seaweed extract. 

What does this have to do with brewing? Well, once they are scooped out, big pumpkins can have a lot of space inside and I decided to try to grow one and ferment a beer inside it. Texas isn’t the optimal place for growing big pumpkins, and I tried to cram too many plants in my garden, limiting the amount of room for them to sprawl, but I did manage to grow a Prizewinner pumpkin that weighed 64-lbs., plus a few other not-quite-that-big pumpkins. My biggest pumpkin was around 16” in diameter and fairly close to being a sphere. Some back-of-the-envelope calculations showed me that, if I scooped the pumpkin out until the walls were very thin, it could put 10 gallons (38 L) of wort inside with at least a gallon (~ 4 L) of headspace. 

For my pumpkin ale, I used a slight variation on my Old Pumpculiar recipe that I published in the October 2004 issue of BYO. (I’ll tack that onto the end of this blog entry.) It’s basically a hombrew clone of the English old ale, Old Peculiar, with pumpkin flesh added to the mash and pumpkin pie spice added at knockout. I think the darker color, slight roastiness from chocolate malt and hints of molasses (which is added during the boil) make an interesting background for the spices. The actual pumpkin flavor — even when the pumpkin is well-roasted — is hard to pick out, but I don’t like making a pumpkin ale that doesn’t contain actual pumpkin. (And, I certainly had more pumpkin flesh than I knew what to do with.) 

One consideration when adding significant amounts of pumpkin to the mash is how much water to add. For this, I used the fact that pumpkin is 80% water to calculate the dry weight of the pumpkin. Then, I calculated the amount of strike water according to my usual formula, which starts with a liquor-to-grist grist ratio of 1.25 qts. of water per pound of grain (2.6 L/kg) and adds in the amount of water under my false bottom. I also added some 6-row malt to the recipe, for some added enzymatic power to deal with the pumpkin starches. 

The brewday went well. This was only the third brew I’ve attempted on my new brewery, but things went very smoothly. This time, the pump worked fine throughout the brewday and I was able to focus on getting my runoff rates slowed down to where I wanted them.  After one or two more brews, I should be to almost the point of familiarity where I was with my old brewery. 

Once the wort was chilling, I started preparing the pumpkins to receive the wort. Whenever I think about vessels for fermenting beer in, my first thought is always if the material is food grade. In this case, there were no worries — the material wasn’t just food grade, it was actual food! The inside of a pumpkin should be sanitary unless it was rotting or had an illness. So, I sanitized a big chef’s knife and brewing spoon to scoop it out. In retrospect, I probably should have wiped down the outside of the pumpkin with a Star San solution, but I’m not going to worry about that. I cut a “lid” into each of the pumpkins and scooped the seeds and “guts” out with the spoon. I didn’t bother shaving out any of the flesh to make more space inside because it was clear, once the “guts” were gone, that I had plenty of room. I poked a hole through each “lid” with a stainless steel racking cane. This hole was just about the right size for a standard fermentation lock. 

My plan was to conduct the primary fermentation in the pumpkins, then rack the beer to a keg after 4 or 5 days. I pitched more yeast than was optimal with the idea of getting the fermentation off to a quick start and headed towards a quick finish. I didn’t want the pumpkins to rot and rupture while the beer was in them. I’m confident that they would hold up for at least a week. And, I’d bet that the carbon dioxide released during fermentation would slow any rotting, which would start in places where the flesh was exposed. But, if I was wrong, I’d have a lot of cleaning up to do. 

What I didn’t factor into my plans was the thermal mass of the pumpkins. The pumpkins were sitting outside in 40 °F (4–9 °C) weather on brewday. After scooping, the biggest pumpkin must have still weighed at least 40 lbs. (18 kg), and probably closer to 50 lbs. (23 kg). All of this mass was at 45 °F (7 °C) or so and the 5 gallons (19 L) of wort — which would weigh about 42 lbs. (19 kg) — was cooled down by the pumpkins, slowing the start of fermentation. So, I added more yeast Thursday afternoon and crossed my fingers. 

The “lids” on the pumpkin fermenters are heavy enough to keep them from being blown off, but aren’t quite air-tight. I’ve done completely open fermentations before, so a tiny amount of oxygen getting into the pumpkins isn’t going to bother me (especially because the beer will be transferred out of them very soon). 

While this is fermenting, I’ve been enjoying my “test brew” IPA and the dry stout from my first “real” brew on my new system. I “doctored” the IPA with some Nelson Sauvin hops, added as a French press extract, and it is now very hop-a-licius. The dry stout is appropriately dry and has a nice roasty character. After tasting it, I don’t think I oversparged, as I was worried about on brewday. It’s maybe a bit too bitter for a dry stout, but not by much. I’m hoping to brew my porter over the weekend, but I’ll have to see if I have the time. 

Here's the recipe:

Old Pumpculiar
(Pumpkin-spiced old ale)
(10 gallons, all-grain)

OG = 1.059  FG = 1.013

IBU = 20  SRM = 25  ABV = 6.0%

Ingredients
15 lbs. British 2-row pale ale malt
2.5 lbs. US 6-row pale malt
1.5 lb. torrified wheat
1.5 lbs crystal malt (60 °L)

6 oz. dark crystal malt (90 °L)
6 oz. chocolate malt
1 lb. cane sugar
16 fl. oz. molasses

6 lbs. baked pumpkin cubes (in mash)
1.5 tsp. pumpkin pie spice (at knockout)
11 AAU Newport hops (60 mins) 1 tsp. yeast nutrient
Fermentis Safale S-04 dried yeast Step by Step

Mash at 154 °F (68 °C). Boil 90 minutes. Ferment in pumpkin.