Actually, it's pretty widely known among historical brewers that unhopped medieval-style English "ale" will sour in a matter of days unless it's of prodigious strength. In my experience, in order to last more than 4-10 days the OG must be strong enough to present 10+%ABV in order to inhibit spoilage microflora from having an effect. These observations confirm contemporary writings on the subject. So I guess it's all down to your definition of "a big hurry".
I've had ciders at 6-7% ABV cellar fairly well, even in wood. I don't know the science behind that phenomenon; I suspect it has something to do with malt having more nutrients available for microflora metabolization than fruit and cane sugars. Historically, handy-books advised fortifying cider which was meant to be laid down. A historical 'receipt' I use annually specifies a substantial amount of sugar added to fresh-pressed juice, cast to cask, pitch 'ale yest', bung it up when it stops actively working and
wait a year. My measurements indicate an ABV of 7-9% depending on the must constituents.
Historically, wines below a certain strength were also sold young, went off very quickly, and were often consumed while still fermenting. The phenomenon of "laying down" bottled wines is actually relatively recent (the last ~200 years or so). The handy-books are stuffed to the gills with methods and receipts for making spoiled wine palatable. It stands to reason, too - sanitation, at least in terms of microflora, was unheard of (if it were, we would never have seen Porter explode in the 18th century). Only the strongest wines would age any appreciable time. Most wines would be in at least the beginning stages of going off when they reached English or American shores from the locales where they were tunned.
The point is, historically the logical conclusion, supported by observation of modern recreated recipes/techniques, is that alcohol was the preservative in unhopped beverages.
In terms of hopped beverages, as Revvy noted one need only skim the history of India Pale Ale to see an obvious example of the preservative quality of hops. Further back in history, the addition of hops was a crucial development in the supplanting of gruitbier in the Low Countries by hopped beer from the Hanseatic ports. From approximately 1400CE on, hopped beer rapidly overtook traditional ale in Britain, Andrew Boorde's xenophobia notwithstanding. Brewing historians conclude that it was economics, not particularly consumer taste, which drove the spread of hopped beer, specifically because the addition of hops made for a more economical brew, as the resulting beer lasted longer and took less malt than unhopped (or gruit) malt beverages.
There's a whole range of sources for all this to cite, too much that's on my shelves in books and advanced-degree dissertations and not on the web.
For the OP, an experiment you may wish to try in order to determine if the flavors are spoilage or simply unbalanced porter: Go buy a bottle of Malta Goya. Malta you're likely to get in DE is brewed at The Lion Brewery in Wilkes-Barre, PA, and IIRC is simply unfermented Stegmaier Porter.
Now, there are hops in there, but not so much as you'd notice. I suspect that your unhopped porter is actually spoiled. I sincerely doubt that the additions you made took the ABV above the point where the beer itself is antiseptic; as I said, I find 10% ABV to be the magic number.
Cheers!
Bob
P.S. Yooper, while I'm the last bloke to wish an argument with a moderator, I must protest. When a desired citation quotes specific portions of a web site or page, a simple link is insufficient; in one of the above examples, Terafan's work is quite lengthy, and expecting the reader to sift through the entire thing to find the lines of interest is unreasonable. Thus one is compelled to quote the relevant passage of text to support one's position. This is commonly-accepted practice in essays; I cannot fathom why it's objectionable here.
