A couple years ago, I brewed a pumpkin ale. The beer was an old ale — an Old Peculiar clone — spiced with traditional pumpkin pie spice. But I decided to take things one step further and ferment the beer inside a pumpkin. That year, I was growing some large pumpkin varieties in my garden. Two of the pumpkins were large enough that I estimated they would hold about 5.0 gallons (19 L) of beer apiece. On brewday, I made 10 gallons (38 L) of wort and cooled it down. While the wort was chilling, I cut the pumpkins open (with a sanitized knife) and scooped out the “guts” (with a large, sanitized spoon). You always want your fermentation vessels to be food grade and pumpkins are not only food grade, they’re actually food. Likewise, you always want your fermenters to be sanitized. And, unless it was diseased, the inside of a pumpkin should not be infected with microorganisms.
One thing I worried about was that the shell of the pumpkin would get soggy, especially when alcohol was present, and rupture while beer was in it. As it turns out, I had nothing to worry about. The pumpkins held up fine during fermentation and even stayed intact for weeks afterwards.
Although this was a fun experiment, there was one drawback — the beer had a raw pumpkin taste, most likely from the contact with fermenter walls. If I try this again, I might try to turn the pumpkin upside down over a heat source and roast the interior. Until then, I’ll just have fond memories of an fun experimental brew.