I’ll just start with why bother. Pumpkin in and of itself adds nothing to the beer. It’s a vegetable with very little going on and little flavor when used alone. Typically it is dosed with spices. If you look at canned pumpkin it has a little bit of salt, and is about 7% carbs and about a percent and a half protein. For the carbs 4 of the 7% are fiber and 3 of the 7% are sugars. The only thing the pumpkin can possibly give to the beer is 8% of the total mass and the sugars will ferment away and the protein will probably fall out in the fermenter. Perhaps some aroma contribution could be gained if no spices were added and the yeast was neutral. What I am saying is the pumpkin is a waste of time and effort, just add spices and end up with the same result.
Let’s take a real world example. My local makes a wildly popular pumpkin beer and uses 1 pound per barrel. That is 16 ounces of pumpkin per 31 gallons of beer. Break that down to a bottle and you would have 0.0484 ounces of pumpkin per bottle or 1.37 grams. That is half the weight of a penny or about the weight of a paperclip. I’d personally call it nothing. So basically they put pumpkin in the beer so it has it, but not enough to do anything. When you calculate only 8% of the mass contributes to the beer that 1.37 grams becomes 0.1 grams or ~1/10th the mass of a small paperclip.
So perhaps a brewery out there uses a significant quantity of pumpkin in their beer. Let’s determine what it would take to become significant. A 10% contribution to the volume would start to be significant which would be 3.1 gallons out of 31 gallons. A standard 15 ounce can is 1.5 cups or 12 fluid ounces. So to make 15 barrels of beer the brewer would need to use 496 cans of puree in order to have a 10% contribution. Even a homebrewer would need almost 6 cans to have a 10% contribution and in reality when only 8% of that is anything useful the real contribution is still only approaching 1%.
I once had a belligerent woman try to convince me her husbands beer had this awesome pumpkin aroma and flavor. It didn’t, but she had convinced herself it did. IIRC he had not used any spices and to me it was a very nondescript pale ale, tasty, but no pumpkin character. So if you are a homebrewer and are making a pumpkin beer, do yourself a favor, get a can of pumpkin and show it to the mash and then put it away to use next year. Spice the beer and voila, pumpkin beer.