The Eighteenth Amendment, was ratified in 1919, and by 1921, according to this article in the January 1921 issue of Popular Science, home brewing was “among the favorite indoor sports”.

It was perfectly legal to make beer or wine at home, with one minor caveat: The final product could have no more than one half of one percent alcohol. Fortunately, however, the magazine provided information about some tests that can be done to measure alcohol content, concluding “the householder has within his reach means by which he can tell where he stands in his domestic brewing and therefore can find scant excuse for pleading ignorance of the strength of the potations made under his roof-tree.”

Curiously, though, while the magazine describes some of the tests, it doesn’t go into excruciating detail as to exactly how they should be carried out. It seems to me, however, that if the householder had a copy of the magazine, and perhaps some of the instruments described therein, he might be able to plead good faith, even if he couldn’t plead ignorance and the official test revealed a result greater than half of one percent.

Even after Prohibition, the 0.5% limit on homebrewing remained in effect until Jimmy Carter signed a repeal of those restrictions in 1978. Curiously enough, if you go to Google and type in “homebrewing during”, it will suggest “homebrewing during prohibition,” but it will also suggest “homebrewing during COVID” and “homebrewing during lockdown.” According to this article, for example, homebrewing supplies are flying off the shelf.

History has a way of repeating itself.