Hey, actually have some experience and interest in a question for once.

We can actually estimate a batch for George Washington's "Small Beer" Now, we can't do a perfect estimate here, since we don't know much about what yeast they may have used, but we can probably get close based on averages.

The recipe is as follows:

Take a large Sifter full of Bran Hops to your Taste — Boil these 3 hours. Then strain out 30 Gall. into a Cooler put in 3 Gallons Molasses while the Beer is scalding hot or rather drain the molasses into the Cooler. Strain the Beer on it while boiling hot let this stand til it is little more than Blood warm. Then put in a quart of Yeast if the weather is very cold cover it over with a Blanket. Let it work in the Cooler 24 hours then put it into the Cask. leave the Bung open til it is almost done working — Bottle it that day Week it was Brewed.

This is a great deal of beer to brew for your typical homebrewer (5 gallon batches are generally the norm today, so we're looking at 6-7x the volume.

So, we start with approximately 33 gallons of the fermentables, hops, and water total (this is called wort). What is a little different here is that the recipe does not call for boiling after the molasses has been added. You'd typically lose quite a bit of water during this process, and actually increase the ABV of the final product. It just says to toss it in and let it cool. We'll estimate a small amount of loss due to evaporation and cooling from boil.

To figure out the ABV (% alcohol) we're going to need to do some conversions. We need the weight in addition to the volume of the fermentables (the molasses, in this case). Using this volume to weight calulator, we can estimate that it was ~35 pounds of molasses.

So, we have 33 gallons of wort. We know we added 35 pounds of molasses. Using [this] (https://www.brewersfriend.com/allgrain-ogfg/) calculator we input the 33 gallons of wort, estimate a gallon is lost during the cooldown, 35 pounds of molasses and use an average yeast strain. Efficiency isn't really relevant here as molasses is pure sugar, it's all going to be eaten until the yeast can't survive due to either high ABV or all the sugar (yeast food) is gone.

So, to sum up, George Washington's "Small Beer" recipe was approximately 3.72% alcohol by volume. In other words, it was a little less than your average light beer (Bud light, Miller lite, Coors light = 4.2%) It also very likely tasted completely awful to our current palates, as it lacks the unfermentables that grains leave in the wort, which give beer it's "body" and other flavors.

In the middle ages is thougth that the beer was around 2%. This is because they drinked it instead of water as it was safer to drink....and also because alcoholism.