"When in doubt, throw it out!” is popular advice for what to do with food that’s been sitting in the refrigerator. Is the food spoiled, or can it be safely eaten? Tasting the food is not advised; the look and smell tests should be used. The “When in doubt, throw it out!” food proverb (also applicable to old medicines) is cited in print from at least the 1920s.
28 April 1927, Alton (IL) Evening Telegraph, pg. 7, col. 4:
Don’t taste food of doubtful quality. The eating of the smallest quantity of botulus-infected food has caused death. When in doubt about food, throw it out, but don’t put it where the chickens or the family dog can get it.
16 June 1931, Wisconsin State Journal (Madison, WI), pg.17, col. 5:
Never use canned foods of which you have any suspicions. Odor and appearance will tell enough, without the risk of tasting. When in doubt, throw it out.
Nutrition for Health
By Holger Frederick Kilander
Published by McGraw-Hill
When in doubt, throw it out. However, foods may be left in opened cans in the refrigerator just as safely as in other containers.
OCLC WorldCat record
When in doubt throw it out!
Author: Michigan. Dept. of Health.
Publisher: Lansing : Michigan Dept. of Health, 
The Modern Encyclopedia of Baby and Child Care
Edited by Benjamin Frank Miller
Published by Golden Press
Item notes: v. 4
A good rule to follow in handling food is: “Keep it cold or keep it hot; when in doubt, throw it out.”
Beware of the Food You Eat
By Ruth Winter
1969 ed. published under title: Poisons in your food.
Published by Crown
The cardinal rule of food safety at home is: When in doubt, throw it out
4 November 1976, Dallas (TX) Morning News, section E, pg. 19:
When in doubt
throw it out
Prevent foodborne illness—throw out food of “questionable” safety, advises Frances Reasonover, a foods and nutrition specialist with Texas Agricultural Extension Service.
Foodborne and Waterborne Diseases: their epidemiologic characteristics
By I. Jackson Tartakow and John H. Vorperian
Published by AVI Pub. Co.
When an item of food, regardless of its cost, is of questionable quality, restaurateurs should heed the slogan, “When in doubt, throw it out!”
The Complete Book of Soups and Stews
By Bernard Clayton, Jr.
New York, NY: Simon and Schuster
Finally, there is this maxim among chefs that should be posted in each soup-maker’s kitchen:
“Keep it hot,
keep it cold,
when in doubt
throw it out!”
All-new hints from Heloise: a household guide for the ‘90s
Edition: reissue, illustrated
Published by Perigee
In fact, never taste-test any type of questionable food, whether it’s canned, home-cooked, carry-out, or even fresh from the market. Always throw out foods that you suspect may be spoiled. When in doubt, throw it out!
Seattle (WA) Times
Originally published August 29, 2007 at 12:00 AM
When in doubt, throw it out
By Karen Gaudette
Seattle Times staff reporter
Many things in life are built to last. Sadly, food is not one of them.
We’ve included guidelines below to help determine whether it’s safe to enjoy Auntie Mia’s famous pickled onions or the old can of creamed corn collecting dust in the pantry.
Food safety is no joke. The Centers for Disease Control and Prevention estimate 76 million cases of food-borne illness occur each year in this country. While most cause only mild symptoms, 325,000 cases send folks to the hospital and 5,000 result in death. The most severe illnesses tend to occur in the very old, the very young, those with compromised immune systems and healthy people exposed to high doses of an organism.
Remember: When in doubt, throw it out.
Palm Beach (FL) Post
When in doubt, throw it out
By Jan Norris
Palm Beach Post food editor
Sunday, May 25, 2008
Do NOT depend on smell or taste to determine safety of foods.
Throw out any meat, chicken, seafood or dairy product, raw or uncooked, that isn’t at 40 degrees or below (look for visible ice crystals).
Use all perishable foods before shelf-stable ones.
Cook perishable proteins — meats, eggs and poultry — first.