Food Protection Connection: Food Spoilage: Safe or Suspect?

(reprinted from Dietary Manager, July 2008)

Sour smell, slimy touch, wilted appearance… dietary managers are always on the lookout for signs of food spoilage. What causes food spoilage? And what’s the connection between food spoilage and food safety? This column will bring you some fresh insights into these questions.

Food Spoilage Basics

Food spoilage is the deterioration of quality that comes from biological, chemical, or physical changes. For example, bread that has become stale has lost moisture. This is a physical change defined by food scientists as a form of “spoilage.” Technically speaking, the bread becomes dry because starch molecules in the bread are slowly forming crystals—and capturing moisture from gluten in the bread to do so.

A type of deterioration that occurs in fresh produce is called chilling injury, which is browning and pitting that results from extended cold storage (typically below 37˚F). Yet another example is chocolate bloom. This is the dull, white streaking we see on a chocolate bar, which actually reflects changes in the crystalline structure of molecules. Bloom is safe, but unattractive. Often, bloom occurs when chocolate is subjected to low or high temperatures (below 27˚F or above 80˚F).

A well-known form of spoilage is freezer burn, characterized by dried-out, light-colored spots on meat. What happens is that ice crystals form in the meat and migrate to the surface, drawing out moisture as they go. Freezer burn, like chocolate bloom, is safe but unappealing. It tends to cause a leathery texture and spotty appearance on meat. Generally, it occurs at frozen meat temperatures above 0˚F, so steady, very cold temperatures can help prevent it. Air-tight wrapping helps prevent it as well.

After produce is harvested or meat is slaughtered, a certain amount of deterioration inevitably begins. Some of this is the simple action of natural enzymes present in the food. In addition, microorganisms that are present (or are introduced during processing, transport, and/or storage) can wreak their own havoc.

More Spoilage Examples

In biological spoilage, bacteria, molds, yeasts, and/or enzymes change the nature of the food. Below are more examples of spoilage processes.

Gauging the Risks

It’s understandable to wonder: Is spoiled food dangerous? In and of itself, loss of quality—such as stale bread—poses no food safety hazards. Spoilage and unsafe food are distinct from each other, even though they sometimes overlap. The FDA notes, “Many people relate food spoilage (sour milk, for example) to foodborne bacteria. Illness-causing bacteria are not the same as food-spoilage bacteria.” (www.cfsan.fda.gov “A to Z” list)

On the flip side, you can’t always count on your senses to pinpoint dangerous foods. The FDA also cautions, “Foods that look and smell fresh may contain pathogens.” Botulism toxins, for example, are undetectable to our senses, so we can’t just clear food of spoilage indicators and then declare it safe.

All in all, even if you believe a spoiled food may be safe, should you serve it to customers? Probably not! After all, food service is about quality as well as safety. Our standards for quality tell us to discard spoiled food and improve the procedures that led to spoilage.

The Good News

The good news for dietary managers is that many of the same steps you take to keep food safe also help control many forms of spoilage. Here are some tips:

• Inspect food products for signs of spoilage on the receiving dock, and reject any product that does not meet both quality and safety standards.
• Monitor sell-by and use-by dates on food products.
• Follow standard operating procedures for storage of all products.
• Maintain consistent food storage temperatures, including frozen food temperatures at or below 0˚F.
• Avoid letting food dwell in the danger zone (40-135˚F). Pay particular attention to lapses that may occur during receipt, stocking, and inventory withdrawal.
• Wrap and/or protect food products during all phases of the flow of food.

Spoilage can show up as changes in flavor, texture, aroma, or appearance. Simple attention to food-safe procedures will help reduce spoilage, and help control food quality in your operation.

Sour Milk
Milk undergoes gradual change as bacteria ferment its lactose (milk sugar) to produce alcohols and acids. Flavor changes, and so does the smell of the product. The characteristic “sour milk” odor comes from lactic acid and related acids produced by bacteria.

Soft Vegetables
Have you noticed that fresh vegetables such as carrots, broccoli, celery, and many others—become soft with age? Certain molds and bacteria produce enzymes that cause this change. The crispness of vegetables comes from its cellulose— a form of carbohydrate we call “indigestible” or “fiber.” The enzymes from microorganisms break down that fiber into smaller molecules that lack “woody” characteristics, reducing the crisp texture.

Slimy Fruit
What about that characteristic sliminess we notice on old fruit or vegetables? This is caused by small sugar-like carbohydrates produced by bacteria. Their slime alters both texture and flavor of these foods by changing their natural sugars to related carbohydrates.

Sulfur or Ammonia Odors in Meat
Bacteria in meat bring about a number of changes. For example, types of Clostridium and other bacteria break down proteins into their building blocks, amino acids, and then into foul-smelling byproducts. The amino acid cysteine breaks down into hydrogen sulfide, along with other components. Enzymes in meat also contribute to conversion of amino acids into other unpleasant-smelling compounds with equally unpleasant names like cadaverine and putrescine… you get the idea!

Rancid Fats
What happens when sweet butter or other fats develop a sour flavor? Certain bacteria and fungi convert the fat molecules into glycerol and various acids. The acids impart characteristic sour flavors.

Moldy Cheese
Everyone has seen patchy mold growth on foods, from cheese to produce to bread to leftovers. Molds, unlike some forms of spoilage, generally do pose a food safety risk. This is because some molds produce toxins (mycotoxins) that can cause illness.

Sue Grossbauer, RD, author of several books, and a regular contributor to DIETARY MANAGER magazine.