How does the Type of Containers Affect the Shelf Life of Bread?
Category: Engineering—Food Technology
Project Idea by: Arielle Simner and Naomi Chalfin
Shelf life is the period during which food may be stored and remain suitable and safe to eat. Two ways of identifying shelf life are date mark and expiration date. A date mark is a date stamped on the food package with instructions that read "use by [date]" or "best before [date]." A "use by" date appears on highly perishable food with short shelf lives such as milk and meats. These items may be dangerous to eat after the date. The "best before" date appears on foods with longer shelf lives such as breads and cookies. These foods are still edible after the date, but their taste quality may not be as good. For example, once the date on potato chips has passed, they will not be bad, just less crisp.
The expiration date on food tells you when you can expect the food to go bad. It doesn't mean that the food will be inedible on that date. Instead, it indicates when the food most likely will start to go bad. Whether a particular food has a longer or shorter shelf life than the expiration date or date mark depends on storing conditions. For example, if milk is left out of the refrigerator for a long time, the milk will probably spoil before its date mark.
The shelf life of food is affected by fat, moisture, oxygen, heat, and time. Foods with more fat spoil faster. Oxygen, moisture, and heat encourage the growth of microbes, which spoil food. So the longer foods are exposed to oxygen (a gas in air), moisture, and heat, the faster they spoil. The shelf life of foods increases if they are kept cool and away from sunlight. Thus, foods should be stored in dark, cool places.
The length of time bread can be stored before it becomes stale (a decrease in the quality of taste, due to age), dehydrated (dried out), or moldy is based on the type of bread and the storage conditions. Some bread is packaged in plastic and some in cellophane. Breads are also stored in different types of open and closed containers. A project question might be, "What type of container increases the shelf life of bread?"
Clues for Your Investigation:
Use different kinds of bread containers including plastic bread sacks, cellophane bread wrappers, and a plastic box with a lid. The shelf life of bread is measured by the freshness of bread. One measure of freshness is its moisture content. Compare the time it takes for bread slices to dehydrate. Design a measuring scale to compare bread dryness. For example, the driest might be 1 and the most moist 10.
Independent Variable: Different types of bread containers
Dependent Variable: Time to reach dryness of 1 on your scale
Controlled Variables: Environmental conditions including temperature, light, and humidity, type of bread, size of samples, same "best before" date
Control: Bread without a container
Other Questions to Explore:
- How does temperature affect the drying of bread?
- Staleness is a measure of the quality of a food's taste. How does temperature affect the staling rate of bread?
- Mold is a sign of old or stale bread. How does water activity affect the growth of mold?
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