“Never mix the grape and the grain” (drinking adage)

“Never mix the grape and the grain” is a drinking adage of unknown authorship. “I will not mix the grape and the grain” was cited in 1940. “Never mix the grain and the grape!” was cited in 1951.
 
An explanation was made in a 1963 newspaper column about drinking on new year’s eve:
 
“When you’re eating, you can mix most anything, as your stomach is getting a lining, but before, don’t mix the grape with the grain—that is don’t follow (the grape) wine, champagne, sherry, port or cognac with (the grain) whisky, beer, vodka or gin. Keep them apart.”
   
New York magazine stated in 1986 that “one must never mix the grape and the grain” was a myth. “Grape or grain, but never the twain” was popularized in Thomas Pynchon’s novel, Mason & Dixon (1997).
 
   
29 December 1940, The Idaho Sunday Statesman (Boise, ID), “Katie Makes 1941 Promises” by Katharine Brush, pg. 12, col. 2:
I will not mix the grape and the grain, of the Republican and the Democrat, or the old school chum and the new professional acquaintance.
     
2 May 1951, Morning World-Herald (Omaha, NE),  “Dry Martinis…Ingredients Escape Debate” by B. F. S. in the Providence Bulletin, pg. 22, col. 5:
Nonetheless, and for all its delights, the dry martini is an insidious drink.Since it violates the first rule of alcoholic beverage consumption—“Never mix the grain and the grape!”—it is an insidious tipple even for men.
 
26 November 1951, Rocky Mount (NC) Evening Telegram, “The Old Second Guesser” by John Wheeler, pg. 14, col. 5:
The old theory was applied — “never mix the grain with the grape.” There were no cocktails or whiskey before dinner, only sherry and dubonnet.
 
Google Books
Gift of the Grape
By Lloyd Eric Reeve and Alice Means Reeve
San Francisco, CA: Filmer Pub. Co.
1959
Pg. 288:
There is also a saying that you should “never mix the grape and the grain.”
 
Google News Archive
31 December 1963, Pittsburgh (PA) Post-Gazette, “It Happened Last Night” by Earl Wilson, pg. 21, col. 7
When you’re eating, you can mix most anything, as your stomach is getting a lining, but before, don’t mix the grape with the grain—that is don’t follow (the grape) wine, champagne, sherry, port or cognac with (the grain) whisky, beer, vodka or gin. Keep them apart.
 
Google Books
The Minister for Justice;
A Novel
By Terence De Vere White
Boston, MA: Gambit
1971
Pg. 7:
“I’d encourage you to try the claret; but I see you are a wise man who doesn’t mix the grain and the grape.”
 
Google Books
With Bold Knife and Fork
By M. F. K. Fisher
New York, NY: Putnam
1979, ©1969
Pg. 278:
But I have an instinctive feeling which may well be mistaken that it is foolish to mix the grape and the grain, and since I like wine better than beer, I usually choose to drink it.
 
Google Books
18 August 1986, New York magazine, pg. 64, col. 2:
One other myth that’s still in circulation is that one must never mix the grape and the grain; that is, if a digestif is served after a wine-oriented meal, it must be a wine-based brandy, such as cognac or armagnac, because only the grape can followt he grape. The fact is, of course, that when wine is distilled into brandy, it no longer bears any relation to wine; what’s more, the wine used to make the finest brandies is very poor stuff, which is why it’s distilled to begin with. It’s true that sipping a fine old cognac is a wonderful way to end an evening, bu only if you enjoy it’s taste;that it comes from grapes is irrelevant. In practice, quite a few wine drinkers find that even the finest brandies keep them up at night, and opt for a whiskey-and-soda instead.
 
Google Books
French Blues:
A not-so sentimental journey through lives and memories in modern France
By Paul Rambali
London: Heinemann
1989
Pg. 30:
I was always warned not to mix the grape and the grain. Wine or brandy, when mixed with beer or whisky, would produce a lethal hangover.
 
Twitter
Marthina Elmqvist
‏@QueenOfelia
Don’t mix the grain and the grape - brilliant @Nigella_Lawson advice
1:42 PM - 18 Dec 2014