EF - Food Preservation Practices Microlesson

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Food Preservation Practices

Quick Glance: Thermal Processing

Do you have a refrigerator or a freezer? Most of you would say “yes" to this question.A refrigerator and freezer temperatures use a type of process called thermal processing.  

If you have a refrigerator, then you might be familiar with the importance of keeping food safe from spoilage. A refrigerator and freezer temperatures use a type of process called thermal processing. Thermal processing is an important part of food preservation. There are two main categories which include hot and cold. You will learn all about these two types of processes in the module ahead.

Explore: Food Preservation

Food preservation is an important topic in the field of Food Science. Knowing how to preserve a food item after it is cooked is important in preventing contamination and spoilage. Before we dive into those processes, it is valuable to review how we harvest and process food.

See the graphic below for a good visual of the process.

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As you can see in the graphic above a couple of thermal processes have taken place. A heat and a cold related process have been used to preserve the freshness and safety of the food item. Within these two categories, there are several processes which can protect food.

Cold Thermal Processes

Refrigeration

The first cooling system for food involved using ice. It was developing in the late 1700’s and early 1800’s. So, in 1834, the first working vapor-compression refrigeration system was built. The first commercial ice-making machine was invented in 1854. William Cullen at the University of Glasgow demonstrated the first artificial refrigeration system in the year 1748. But, Oliver Evans, designed the first refrigeration machine that didn't use liquid and instead used vapor to cool. Can you imagine life without these modern conveniences? Before this invention people would put food in holes and pack it with ice and snow. They would also use the basement area of the house where it is naturally cooler. Nowadays, almost everyone in the United States has a refrigerator of some sort. Let’s look a little bit closer at the benefits of a refrigerator.

Refrigeration benefits

  • Slows down the respiration process in food or the food spoilage
  • Slows the growth of microorganisms
  • Used in the medical field to store vaccines and embryos
  • Enables the transport of climate-sensitive food

 

Freezing

Freezers appeared during the 1940s, but were not put into production until after World War II. Refrigerators advanced in time and automatic defrosting and automatic ice making appeared in 1950s and 1960s. Freezers are sold as a stand alone unit or a compartment in your refrigerator unit. Freezing food provides a longer shelf life for cooked food than your standard refrigeration method. The chart below provides a good guideline on how long to keep certain foods depending on their preservation method.

The freezing process is best used on-

  • Food can be frozen at its peak of ripeness for the best taste
  • Frozen food can be more economical than fresh depending on the season
  • Convenience: Just pull it out of the fridge and de-thaw
  • Suspends microbial and bacterial growth

The chart below provided by the Food and Drug Administration (FDA) gives us a good idea of which food should be refrigerated or frozen and the length of time that is recommended for each food item.

 

Heat Preservation Methods

Blanching

The word blanch refers to a cooking technique in which food is briefly immersed in boiling water or fat. This softens the food so it can be used later in quick-serve foods like stir fry and casseroles. It is best to put blanched veggies into an ice bath right after to stop the cooking process. If not, they will continue to cook and become soggy. Blanching also cleanses the surface of dirt and organisms, brightens the color, and helps retard the loss of vitamins.

Benefits

  • Prevents color and flavor loss before freezing
  • Helps to remove the skin more easily from certain fruit and veggies
  • Helps to kill certain microorganisms

Pasteurization

Pasteurization is the process of heat processing a liquid or a food to kill pathogenic bacteria to make the food safe to eat. Louis Pasteur was able to demonstrate that abnormal fermentation of certain beverages could be prevented by heating the beverages to about 135 degrees F. This would kill certain types of bacteria and other diseases that were common at the time.

Benefits

  • A cost-effective way to treat dairy products
  • Extends the shelf life of juices up to a year
  • Does not cause much change to the look, taste, or feel of the food. 
  • Generally quick process

 

Commercial Sterilization

Commercial Sterilization is the process of intense heat applied to food to render food free from microorganisms capable of growing at certain temperatures. This process is done on a large scale and very high temperatures. This is best used for meats, fruits, and vegetables and can give many food items an extended shelf life. Foods using this process can last anywhere from 1-5 years.

Benefits

  • Can mass-produce product
  • Extends the shelf life safely
  • Good for meat, fruits, and vegetables

Click HERE Links to an external site. to access the FDA Storage Chart to learn more about refrigerator and freezer storage.

Challenge

So do you think you know about food preservation? Try the challenge below to test your knowledge.

 

Takeaway: What Is Your Takeaway?

What is freeze dried?Takeaway.png 

You know about freezing and refrigeration, but do you know about the process of Freeze Drying? Freeze-drying is a three-step process. The first couple of steps involve freezing food and then placing the food in a vacuum chamber under low heat. The frozen water crystals evaporate directly from ice to water vapor in a process called sublimation. Using slightly higher temperatures the remaining bit of water molecules are expelled by a second drying process due to the heat. The food is nitrogen sealed for storage to prevent contamination from water or oxygen.

Using this process, food can last years in storage. Many emergency food companies sell packages of this type of food so people can be prepared in case of a storm or natural disaster. Although it does take more energy to process this food, it is a good option when preparing for the future or a disaster. Most freeze-dried foods just need to be re-hydrated with a little bit of water and can be quite tasty!

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