The jokes write themselves with this one, so I’m going to try to keep it as straight as possible: brewing with peas is an ancient tradition, going back at least 400 years in Britain, and it still takes place in Lithuania, the United States and Japan.
The earliest mention I have found for peas in beer is from Gervase Markham’s The English Housewife, published in London in 1615:
Now for the brewing of the best March Beer, you shall allow to a Hogshead thereof a quarter [eight bushels] of the best Malt well ground, then you shall take a Peck [a quarter of a bushel] of Pease, half a peck of Wheat, and half a peck of Oats and grind them all very well together, and then mix them with your Malt …
This, Markham said, would make “a Hogshead of the best and a Hogshead of the second, and half a Hogshead of small beer, without any augmentation of Hops or Malt.” Even though the hop rate was just a pound a barrel, the strong beer, brewed in March or April, “should (if it have right ) have a whole year to ripen in”, Markham said, and “it will last two, three, or four years if it lye cool; and endure the drawing to the last drop.” That is probably more down to the strength of the beer – at some five and a half bushels of fermentables per barrel, the alcohol per volume was quite likely north of 11 per cent – than any magic the peas brought to the brew.
A few words about the word “pea”, incidentally: it began as “pease”, singular, with “peasen” the plural. By the 15th century “pease” was often being used as both the singular and plural, and as a “mass noun”, like rice or malt. Eventually , by the 17th century, “pease” was misanalysed as the plural of a singular “pea”. “Pease” and “peasen” survive today only in “pease pudding” and in place names such as Peasenhall in Suffolk.