I'd like those sources, too, please!
Washington's molasses 'porter' dates from his time being whupped by the French (1750s) near Fort Duquesne (Pittsburgh). Here is the receipt:
To Make Small Beer
Take a large Siffer full of Bran Hops to your Taste. Boil these 3 hours then strain out 30 Gall into a cooler put in 3 Gall Molasses while the Beer is Scalding hot or rather draw the Melasses into the cooler & Stain the Beer on it while boiling Hot. let this stand till it is little more than Blood warm then put in a quart of Yest if the Weather is very Cold cover it over with a Blank't & let it Work in the Cooler 24 hours then put it into the Cask -- leave the bung open till it is almost don Working -- Bottle it that day Week it was Brewed."
I have brewed this. It is, without exaggeration, perfectly foul. Even after aging for six months, it was utterly revolting. I made the mistake of brewing five gallons of it (not the original receipt, but redacted for five gallons); I had to dump all but the sample bottles.
I don't think the recipe the OP posted is at all correct, either; it's a modern idea of what a Colonial beer might have been.
In the first place, it's written like a modern homebrew recipe, with modern ingredients.
In the second place, Jefferson didn't share his receipt or procedure in writing. In fact, the link Revvy posted says:
"I have no reciept [sic] for brewing," Jefferson replied, "and I much doubt the operations of malting and brewing could be successfully performed from a reciept. If it could, Combrune's book on the subject would teach the best processes: and perhaps might guide to ultimate success with the sacrifice of 2. or 3. trials. . . . We are now finishing our spring brewing. If you have a capable servt. and he were to attend our fall brewing, so as to get an idea of the manual operation, Combrune's book with a little of your own attention in the beginning might qualify him."
I have copies of Combrune in PDF (30MB) and Text (<0.5MB) should anyone want them. The PDF is sufficient to print a facsimile of the original; the TXT file has some OCR errors in it.
Whee! Historical brewing!