“Lunatic soup” is slang used in Australia and New Zealand for an alcoholic drink. “A lively and humorous Temperance address by the Rev. W. H. Coates, who took as his text the words ‘Lunatic Soup,’ as a soubriquet for drink” was cited in the Hendon (a suburb of London) Courier in 1887, but it’s not known if this citation influenced the later citations in Australia and New Zealand.
 
“A man under the influence of ‘lunatic soup’” was cited in a New Zealand newspaper in 1920. “People who had taken ‘sedna’ as a beverage had stated it was like ‘lunatic soup’” was cited in an Australian newspaper in 1925.
 
New Zealand-born lexicographer Eric Partridge (1894-1979) wrote that “lunatic soup” meant cheap red wine. Citations in 2009 and 2010 define “lunatic soup” as cider.
 
   
(Oxford English Dictionary)
lunatic soup n. Austral. and N.Z. slang alcoholic drink.
1933 Bulletin (Sydney) 6 Sept. 42/1   Lunatic soup, as the few fellows about who knew him as Darkie called the brandy he drank.
 
28 April 1887, Hendon (Middlesex, England) Courier, “Church of England Temperance Society, Child’s Hill,” pg. 8, col. 3:
But the chief interest of the evening was centred in a lively and humorous Temperance address by the Rev. W. H. Coates, who took as his text the words “Lunatic Soup,” as a soubriquet for drink, and shewed the madness of taking drink by a number of illustrations. The family the looks, the purse, according to his shewing, were all the worse for “Lunatic Soup,” and whatever other soups the audience might indulge in, he warned them against this as bad for their tempers, their pockets, and their complexions.

Papers Past
6 October 1920, Ohinemuri (New Zealand) Gazette, “Offering a Premium to Steal,” pg. 2, col. 5:
During a hearing of a theft case at Te Aroha on Monday, in which a man under the influence of “lunatic soup” was charged with stealing some clothing from the shop fronts of local business premises, ...
 
Google News Archive
19 February 1925, The Age (Melbourne, Australia), “An Intoxicated Motorist: The Effects of Tonic Wine,” pg. 11, col. 5:
People who had taken “sedna” as a beverage had stated it was like “lunatic soup.”
 
Google News Archive
23 January 1930, The Age (Melbourner, Australia), “Sleeping It Off: Drunken Driver Driven to Watch House,” pg. 13, col. 4:
Mr. Stafford, P.M., in discharging Lecworthy, advised him not to drink “lunatic soup” in future.
 
Google News Archive
19 February 1967, The Sun-Herald (Sydney, Australia), “Aussie Most Colorful Language,” pg. 13, cols. 3-6:
He is New Zealand-born Mr. Eric Partridge, whose new “Dictionary of Slang and Unconventional English” came out this week.
(...)
If he’s a drinking man he’ll either join his mates “on the wallaby” (drinking bout) for a “beer up” or be happy with an occasional “barmaid’s blush” (mixture of port and lemonade, or rum and raspberry), or some “lunatic soup” (rough red wine).
 
OCLC WorldCat record
Lunatic Soup
Author: S M F Cassidy
Publisher: Winnellie, N.T. : Pandanus Publishing, 2002.
Edition/Format:   Book : Poetry : English
 
Google Books
An Introduction to English Slang:
A Description of its Morphology, Semantics and Sociology
By Elisa Mattiello
Milano: Polimetrica
2008
Pg. 185:
lunatic soup “alcoholic drink of poor quality” (cf. lunatic “insane”).
 
OCLC WorldCat record
Lunatic soup : a true story of murder, mayhem and madness in maximum security
Author: Andrew Roderick Fraser
Publisher: Prahran, Vic. : Hardie Grant, 2008.
Edition/Format:   Book : EnglishView all editions and formats
Summary:
“Andrew Fraser’s experiences in prison and the Peter Dupas murder trial”—Provided by publisher.
   
Urban Dictionary
lunatic soup
any form of cider.
(...)
by the yurrrr merchant Dec 31, 2009
 
Ballygarella
WEDNESDAY, JULY 7, 2010
Planning to brew some lunatic soup
Lunatic soup, madman juice, call it what you like, there are surely hundreds of nicknames. The first alcoholic tipple to befuddle my senses, a sweet nectar that, in my late teens, could in one minute, turn me into a stand-up comedian, and the next, whip my legs out from under me and throw me to the ground. I am speaking, of course, of cider.