Food Processing and Preservation

I

Introduction

Food Processing and Preservation, branch of manufacturing that transforms raw animal, vegetable, or marine materials into tasty, nutritious, and safe food products. The industry has its roots in ancient times, as humans have always needed to obtain food and store a portion for later use. Prehistoric humans may have dried fruits in the sun and stored meat in cold areas, such as caves. The modern food processing and preservation industry was born in 1809, when French chef and inventor Nicolas Appert, searching for a better way to provide food for Napoleon’s army, devised a method for sterilizing food in tightly sealed glass bottles.

Today a wide variety of methods are available to maintain and enhance the appearance and taste of food. Food processing and preservation methods also create products that are convenient for consumers, such as products that are ready to eat or require minimal preparation and cooking. Combining these methods with modern distribution networks makes seasonal crops available year-round in grocery stores all over the world.

II

Processing and Preservation Methods

Food processing encompasses all the steps that food goes through from the time it is harvested to the time it arrives on supermarket shelves. At simplest, processing may involve only picking, sorting, and washing fruits and vegetables before they are sent to market. Some processing methods convert raw materials into a different form or change the nature of the product, as in the manufacture of sugar from sugar beets, oil from corn or olives, or cheese from milk. Processing may also involve an extremely complex set of techniques and ingredients to create ready-to-eat convenience foods.

Food preservation refers specifically to the processing techniques that are used to keep food from spoiling. Spoilage is any change that makes food unfit for consumption, and includes chemical and physical changes, such as bruising and browning; infestation by insects or other pests; or growth of microorganisms, such as bacteria, yeast, and molds.

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Some food preservation techniques destroy enzymes, proteins that are present in all raw foods, which are responsible for the chemical and physical changes that naturally occur after harvesting. Food preservation techniques also help eliminate the moisture or temperature conditions that are favorable for the growth of microorganisms. As they multiply and grow, microorganisms are capable of causing food-borne illness. They also break down foods, producing unpleasant changes in taste, texture, and appearance—changes that we recognize as spoilage. Although people have known about spoilage and some preservation methods to prevent it for centuries, it was only in 1857 that French chemist Louis Pasteur demonstrated the role of microorganisms in the process.

A

Curing

Curing is one of the oldest forms of food preservation. It is used to preserve meat and fish, yielding common products such as bacon, ham, frankfurters, and corned beef. Curing involves adding some combination of salt, sugar, spices, vinegar, or sodium nitrite to animal foods. Smoking, a flavoring technique and preservation method, is another ancient technique that is commonly used with curing. Smoking involves cooking meat or fish very slowly over a low wood fire. Curing and smoking preserve food by binding or removing water so that it is not available for the growth of microorganisms. These methods impart a distinctive color and flavor to food and, in some cases, eliminate the need for refrigeration. Some studies, however, show that curing agents such as sodium nitrite may combine with other chemicals to form cancer-causing nitrosamines. In addition, cured products tend to be very salty, and the sodium in salty foods has been linked to hypertension, also known as high blood pressure. Smoked meats and fish may contain toxic and even carcinogenic compounds that they absorb from wood smoke.

B

Drying

Cultures throughout the world have used drying to preserve food, probably since prehistoric times when people learned that dried foods—for example, fruits left out in the sun—remain wholesome for long periods. In modern times, the dried foods industry greatly expanded after World War II (1939-1945) but remains restricted to certain foods, including milk, soup, eggs, fruits, yeast, some meats, and instant coffee, that are particularly suited to the process. Three basic methods of drying are used today: sun drying, a traditional method in which foods dry naturally in the sun; hot air drying, in which foods are exposed to a blast of hot air; and freeze-drying, in which frozen food is placed in a vacuum chamber to draw out the water.

Removing the water preserves food because microorganisms need water to grow and food enzymes cannot work without a watery environment. Removing the water also decreases the weight and volume of foods, thereby reducing transportation and storage costs. However, dried foods may be less convenient for consumers because most must be rehydrated before consumption. In addition, most dried foods only reabsorb about two-thirds of their original water content, leaving the rehydrated product with a tougher, chewier texture than the original. Some scientists and consumer groups have raised concerns about the sulfites commonly added to fruits before drying to prevent browning. These chemicals may cause severe allergic reactions in people with asthma or other people sensitive to the chemicals.

In freeze-drying, frozen food is placed in a special vacuum cabinet. There, water escapes from the food by sublimation, a process in which ice changes from a solid directly to a vapor without first becoming a liquid. Freeze-dried foods retain their original flavor, texture, and nutrients upon rehydration but must be packaged in moisture-proof, hermetically sealed containers. Freeze-drying is an expensive process used for such products as instant coffee, dried soup mixes, strawberries, mushrooms, and shrimp. Flash freezing is a process of supercooling foods to temperatures of -195°C (-320°F) through the use of liquid nitrogen. The process reduces cellular deterioration and increases retained moisture so that foods are tastier when they are unfrozen.

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