“Yum” is used to express satisfaction, especially in regard to food that one has tasted. The food can be described as “yum-yum,” “yummy,” and even “yum-o.”
 
“Yum-yum” (also “yum-yum-yum”) was the slang sensation of 1875, although a citation appears in 1870. The origin is unclear; it may have come from a play or a song from London. The term was used, in its early form, to describe an attractive female. A female character in the Gilbert & Sullivan comic opera The Mikado (1885) is called “Yum-Yum.”
   
“Yum yummy” (also “yummy yum”) was used by at least 1895. “Yumptious” (yummy + scrumptious) is cited in print from 1957. Television cook Rachael Ray has used “yum-o” since at least 2005-2006.
 
 
Rachael Ray—Rachael-isms
YUM-O!
I say this if something is so good that “yum” just isn’t enough of an exclamation. The accent is on the “O” as in, “Oh! That is so good!”
 
Wikipedia: The Mikado
The Mikado or, The Town of Titipu is a comic opera in two acts, with music by Arthur Sullivan and libretto by W. S. Gilbert, their ninth of fourteen operatic collaborations. It opened on March 14, 1885, in London, where it ran at the Savoy Theatre for 672 performances, which was the second longest run for any work of musical theatre and one of the longest runs of any theatre piece up to that time. Before the end of 1885, it was estimated that, in Europe and America, at least 150 companies were producing the opera. The Mikado remains the most frequently performed Savoy Opera, and it is especially popular with amateur and school productions. The work has been translated into numerous languages and is one of the most frequently played musical theatre pieces in history.
(...)
Roles
The Mikado of Japan (bass-baritone)
Nanki-Poo, His Son, disguised as a wandering minstrel and in love with Yum-Yum (tenor)
(...)
Yum-Yum, A Ward of Ko-Ko, also engaged to Ko-Ko (soprano)
 
Merriam-Webster Dictionary
Main Entry: yum–yum
Pronunciation: \ˈyəm-ˈyəm\
Function: interjection
Date: 1878
—used to express pleasurable satisfaction especially in the taste of food
 
Merriam-Webster Dictionary
Main Entry: yum·my
Pronunciation: \ˈyə-mē\
Function: adjective
Inflected Form(s): yum·mi·er; yum·mi·est
Etymology: yum-yum
Date: 1899
: highly attractive or pleasing ; especially : delicious , delectable
   
(Oxford English Dictionary)
yum, int.
[Echoic.]
An exclamation of pleasurable anticipation, with implication of sensual or gustatory satisfaction; freq. reduplicated as yum-yum, etc.
Some of the reduplicated examples are not clearly distinguishable from those given s.v. YUM-YUM n. and a. below.
1878 Burlington Hawkeye in Irish Monthly VI. 688 How we would like to get hold of the man… Alone. In the woods, with a revolver in our hip-pocket. Revenge is sweet; yum, yum, yum.
1899 KIPLING Stalky 239 Pretty lips..Seem to sayCome away. Kissy! come, come!.. Yummy-yum-yum!
1922 JOYCE Ulysses 173 Kissed her mouth. Yum.
1942 O. NASH Good Intentions 143 And fish are only something about which some people say, ‘Yum yum, right out of the water and fried to a delicate golden brown.’
1959 ‘J. CHRISTOPHER’ Scent of White Poppies iii. 40 When she had gone, Bella said: ‘Yum-yum. Really luscious.’
1962 A. LURIE Love & Friendship iii. 45 Miranda cut a piece of warm coffee cake, handed it to Emmy… ‘Oh, yum. Thank you.’
1982 S. PARETSKY Indemnity Only xii. 155 ‘Lotty talked her into..making homemade enchiladas, yum-yum.’ ‘Yum-yum,’ the two little girls chorused.
   
Hence yummy a. colloq., delicious, delectable; also as int.
1899 [see YUM int.].
1934 WEBSTER, Yummy adj.
1950 ‘S. RANSOME’ Deadly Miss Ashley xii. 147 Lora’s attractive face or Dorothea’s yummy figure.
1955 J. P. DONLEAVY Ginger Man xix. 213 Sitting, facing one another across the white table. Bacon and eggs, tea, bread and butter. Yummy.
1955 H. KURNITZ Invasion of Privacy (1956) vi 47, I adore movie stars. Gregory Peck! Yummy!
1970 P. ZELVER Honey Bunch xx. 96 Thanks a lot for the lemonade. It was yummy.
1979 Evening Standard 18 Sept. 23/2 Mr. Zamoyski is a handsome devil himself—such a yummy photograph on the back of the jacket.
 
13 January 1870, Cincinnati (OH) Daily Gazette, pg. 2:
Cheer up, Sixty-Nine-ye’r,
With egg-nogg’d emotion,
To-morrow our parting must be;
We’ll rail the plains over,
We’ll cross the wide prairie,
We’ll steam the day over for thee.
“Yum, yum, yum!”
   
Google Books
Little Folks
By Cairns Collection of American Women Writers
Published by S.E. Cassino, 1872
Item notes: v. 4  
Pg. 46:
I put in my thumb,
And I pull out a plum,
What a brave boy am I !
And here it is — a very splendid plum —
Ain’t it nicey — ab, ha— ha ! yum, yum!
[Eats plum.]
   
Google Books
The Asbury Twins
By Sophie May (Rebecca Sophia Clarke—ed.)
Boston, MA: Lee and Shepard
1875
Pg. 212:
“For the simple reason that you can’t flirt with him. A man that has been through what he has will keep clear of love-affairs, you may depend.”
 
“Yum! yum!” said Vic, laughing, and ran down to her music.
 
16 February 1875, Critic-Record (Washington, DC), pg. 3:
“All your countrywomen,” said Kalakaua to a San Francisco interviewer, “I think lovely and spirituelle, but I give my preference to those of Washington, Boston, and St. Louis.” Yum, yum, yum!
 
6 July 1875, Galveston (TX) Daily News, pg. 1, col. 3:
And now we hear that “a Kentucky girl has a skin white as snow and soft as velvet, and shoulders and bosom like Juno, and a redundant voluptuousness that would turn one’s hair gray in a single night.” Yum, yum, yum!
 
2 September 1875, Indianapolis (IN) Sentinel, pg. 4:
“Yum, yum, yum.”—Journal.
 
This form of criticism, argument, or wit, the Sentinel does not understand. The Journal has used it twice during the last five or six days in connection with extracts from the Sentinel. The Sentinel is not rusty in Latin, has not forgotten all about Greek, can wrestle successfully with Hebrew, and might be provoked into a discussion in Sansacrit, and as for French, Spanish and Italian, it has them all at its tongue’s end, but to tackle this “Yum, yum, yum” of the Journal is about as formidable a task as ever assailed us.
   
17 December 1875, Cincinnati (OH) Daily Enquirer, pg. 4:
Yum, Yum, Yum!
[Washington Cor. New York Graphic.]
Mr. Manton Marble, of the New York World, is passing a few days with Mrs. Eames, of this city.
 
29 January 1876, Cincinatti (OH) Daily Enquirer, pg. 4:
CLEVELAND PLAIN DEALER: True to woman’s nature, our Washington correspondent has turned match-maker, and intimates that Milton Sayler, of Cincinnati, has been captured by a Philadelphia belle. Yum! yum!

2 June 1876, San Francisco (CA) Bulletin, pg. 4:
When two lovers, who fancy they are unobserved, are sitting all alone in the gloaming, with their heads very close together, it sounds like the crack of doom for somebody at the window opposite to yell out, “Yum! Yum! yum!”—Brooklyn Argus.
 
Chronicling America
29 November 1885, St. Paul (MN) Daily Globe, pg. 13, col. 5:
Miss Abott was attired in her Yum-Yum dress and looked as Yum-Yummy as a petite, plump figure in clinging, slimpy garments and a piquant face could look.
   
Google Books
A Dictionary of Slang, Jargon & Cant
By Albert Barrère and Charles Godfrey Leland
The Ballantyne Press
1890
Pg. 428:
Yum-yum (London), first-rate, elegant.
   
20 February 1895, Logansport (IN) Journal, pg. 7, col. 1:
“When the pies come out of the oven the under crusts are crisp and crackling, and just ‘yum yummy.’ It makes me pie-hungry to think of them.”
       
Chronicling America
20 October 1898, Omaha (NE) Daily Bee, pg. 6, col. 7:
‘Twas a gastronomic dream
‘Hard to beat!
And the caramels and gum,
Marguerite,
I can hear your yummy-yum,
Low and sweet.
   
4 August 1957, Syracuse (NY) Herald Journal, pg. 56, col. 4:
The other chose, as usual, the “Sabayon Fielding”—a yumptious creation which the inventor was kind enough to name in our honor several years ago.
 
LIWeddings.com
Re: hmmm Cake flavors and fillings which ones are the best????
We’re having chocolate cake with rasberry mousse. YUM-O!
Posted 2/3/05 6:47 PM
 
Google Books
Yum-O!: The Family Cookbook
By Rachael Ray
Published by Clarkson Potter/Publishers
2008
 
(Trademark)
Word Mark RACHAEL RAY YUM-O
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