Should you throw moldy bread in the trash, or just trim around the green spot? Can Sunday's leftovers be Friday's meal? Failure to know this information could adversely affect your health. For some people , like the elderly, the young, and ill; not knowing could prove deadly.

Scientists have developed methods to detect food spoilage, but until these are available on a mass scale, food science and safety experts have some tips.

Slimy, stinky, spotty or chunky changes in food don't mean very much in terms of safety. It may not taste good, but that doesn't mean it's going to make you sick. That's because there's a difference between what food scientists call spoilage bacteria and pathogens. Spoilage bacteria form into slimy films on lunch meat, soggy edges on vegetables or stinky chicken. But the pathogens that do make you sick are odorless, colorless and invisible.

For leftover food to be safe, it must be kept no more than four days at 40 degrees Fahrenheit or 4 degrees centigrade. (Freezing fresh food at zero degree Fahrenheit will keep it safe indefinitely.) Forty degrees Fahrenheit buys people three days for safety with raw chicken and ground beef, three days with cuts of beef and lamb, and four days for leftovers. Allowing anything to go above the cold 40 degrees along the way from store to frying pan can make the difference between illness and safety according to food safety experts.

A study commissioned by the Federal Transit Administration, cites several issues surrounding food safety. According to the report, about 25 percent of the refrigerators in the country are operating at a temperature that can make food unsafe. This is alarming especially since the refrigerator is used as a food safety device and most people have no clue, no idea what temperature it should be."

If your store bought food was mishandled in transit to the grocery store or while there (think consumer leaving meat in cart and grocery employee putting it back on the shelf for instance) then if your purchase such an item you are already at risk. If it's contaminated and then you further abuse it temperature-wise, by taking too long to get your items home, in the refrigerator - or you are placing it in a refrigerator that is 42 degrees Fahrenheit for instance, instead of the recomended4 0 degrees Fahrenheit or less then you're at risk.

Bad Food Safety Habits that you can Change

Shopping Tips   

• Shop for groceries when you can take food home right away so that it does not spoil in a hot car. When shopping always make sure that you buy the freshest fruits, vegetables, meats and processed foods (if you buy processed foods at all!). 
• Avoid spreading bacteria to other foods. Separate raw, cooked, and ready-to-eat foods while shopping, preparing, and storing.
• When purchasing fish, poultry and beef inspect the items and check the sell by date.  Look for products that looks fresh and that doesn't  smell.   Other foods such as dairy and cheese need to have a stamped sell by date, so make sure you check it out. 
• When shopping buy perishable food such as meat, eggs, and milk last.
• Basically use common sense when storing and eating stored food. Best rule to follow: "When in doubt, throw it out". It is much cheaper to throw out bad food than it is to pay expensive medical bills or miss work.

• Refrigerate or freeze meat, poultry, eggs and other perishables as soon as you get them home from the store.   
• Never let raw meat, poultry, eggs, cooked food or cut fresh fruits or vegetables sit at room temperature more than two hours before putting them in the refrigerator or freezer (one hour when the temperature is above 90°F).
• Never defrost food at room temperature.
• Do not over-stuff the refrigerator.  Cold air must circulate to help keep food safe.
• Check your fridgerator temperature regularly.
• Divide large amounts of leftovers into shallow containers for quicker cooling in the refrigerator.
• Use or discard refrigerated food on a regular basis. 
• Check the Cold Storage Chart for optimum storage times.

"Bacterial growth is time and temperature dependent" said Eileen Dykes of the USDA Meat and Poultry Hotline. Dykes recommends a time limit of two hours between meal to fridge transport, which is not always enough time "if you go to a restaurant and then get a doggy bag, and then go to a movie."

Watching a thermometer in the fridge and counting days on the calendar does far better for home food safety than searching for funny smells or sites of mold. But that doesn't mean those disgusting signs are useless.Use smell, site and objective data, like the refrigerator temperature, and cold food storage chart data to help you reach a educated decision.

• USDA Meat and Poultry Hot Line, 1-888-MPHotline,1-888-674-6854. answers to your questions on... Safe food storage, handling, preparation, Product dating, Product content,  Power outages and much more!
• USDA Food Safety Recalls. Information on the latest food safety issues. Get information about recalls and public health alerts that involve meat, poultry or processed egg products. Receive Email Notification of Recall Updates.Sign up to be notified when recalls or health alerts are issued. 
• Food Cold Storage Chart. The cold storage chart can provide you with important food safety information. 

• ABC News August 12, 2008
• USDA Food Inspection Service
• Food Safety Tips You Can Do at Home to Minimize the Risk of Food Poisoning, July 2008.