Growing giant pumpkins and fermenting beer inside them was a fun side project this year, and I was just thinking about one thing I learned and what it might mean. I learned that pumpkins will remain intact with fermenting beer inside them far longer than I thought. This year, I fermented inside the pumpkins for 5 days, then racked to a secondary fermenter. I racked after 5 days because I was going to visit my folks for the holidays and didn't want to mop up 10 gallons of pumpkin ale when I returned. After racking, I put the lids back on the pumpkins and set them in my back yard. 

When I returned home, 10 days later, I was surprised to see that the pumpkins were virtually unchanged. (Note: it did not freeze during the time I was away.) I could see a little discoloration where I had cut them open, but they were still looking good and a quick thump on the sides suggested that they were still in good shape. It was another 10 or so before they started to show any noticeable signs of rot. 

By the time the pumpkins started to rot, I was amazed that they lasted so long. Compared to my memories of how long it took for a Halloween Jack-O-Lantern to go bad, these pumpkins seemed to keep for a very long time. Then it occurred to me — I'll bet that fermenting the beer inside them actually acted as a preservative. 

A beer fermentation produces a lot of carbon dioxide. At the very beginning of fermentation, this gas dissolves into the fermenting wort. Soon, however, the wort becomes saturated with carbon dioxide and it begins to bubble. Inside the pumpkin, I would bet that a decent amount of gas diffuses into the walls and that this acts as a preservative. 

I don't have any evidence to prove this, but it makes sense. One thing I didn't check was how far into the flesh of the pumpkin, the beer absorbed. I brewed a dark beer, so splitting the pumpkin walls afterwards should have let me see this. I doubt the beer penetrated far, but it makes sense that carbon dioxide would penetrate the walls of the pumpkin at least as far as the liquid, and likely further. 

So, the next time I try this, I am not going to be so quick to rack the beer out of the pumpkin. I am confident that I could let the wort/beer sit in the pumpkin for at least 10 days.