FDSC105:
Lesson 9: Food Processing
Lesson 9: Food Processing Overview
Introduction
Lately, the p-word (processing) has become a word with negative associations when it comes to food. It is often used in the same context as poor nutrition, health consequences, and even addiction (as in your-favorite-processed-food is “addicting”). In this lesson, we will learn about who processes our food, how food processing is done, and what the results are of food processing.
Objectives
Here are the objectives for this lesson:
- Identify the size of the food processing industry.
- Explain how select foods are processed start to finish.
- Give examples of the effects of processing on food’s nutrients.
Lesson Readings and Activities
By the end of this lesson, make sure you have completed the readings and activities found in the Lesson 9 Course Schedule.
Food Processing
Some foods can be made at home or made commercially, for example applesauce and whoopie pies (Ho Hos). What is the difference, if any, between foods made at home and their counterparts made commercially? Food processing has become a significant topic of conversation in the professional media as well as social media platforms. We will discuss examples of how food is processed as well as what happens to the nutritional value of food after processing.
It is likely that processing (cooking) food played a role in our biological development but it also serves other functions. First, raw commodities are sometimes toxic! Foods like raw beans, certain mushrooms, and cassava, (a root like potato, commonly eaten in Africa) can be toxic. Second, raw commodities are perishable. They don’t last forever; they’re essentially slowly dying after the point of harvest.
So we transform raw and perishable commodities so that they have and/or maintain their nutritional and economic value. For example, fresh green beans are often frozen. We also diversify large crops such as corn. We are very good at producing corn and there’s only so much you’ll eat of it in one form. We can create different types of foods and ingredients from the one starting material.
Another example is milk. We almost always pasteurize milk to make it less perishable (and safer) and we frequently transform it into other dairy products, such as cheese, sour cream, butter and yogurt.
Food processing has been performed for thousands of years. More than 10,000 years ago, we began drying, and baking food in a primitive way. 5,000 to 7,000 years ago, the first foods were fermented. We began salting and pickling food maybe 3,000 years ago. In the late 1800s, canning and packaging food became common. More recently, in the early 1900s, freezing food as a way of preservation was developed (although people living in the extreme north have been freezing food during the winter for thousands of years). New technologies continue to be developed.
Fermenting food is one of the earliest means of intentionally preserving foods! No purified or synthetic chemicals were available at that time. No plastic packaging, and little salt was around. It’s only more recently, as in the last century, that we developed more complex and energy intensive technologies like freezing.
Processing serves a lot of functions. Though it likely began as a way to prevent spoilage, not all processes help preserve food. We’ll discuss food spoilage more in a later lesson.
Processing has an effect on food cost. Figure 9.3 is a snapshot of the USDA’s food dollar.
Imagine you’re at the grocery store. Any given dollar you spend on food can be broken down as about 17% going to the farmer who raised the food/ingredients and 83% to other parts of the food system. More specifically, processing accounts for about 16% of your food dollars. These proportions have changed somewhat over time and more recently farmers have been recouping a bit more of our food dollars with movements like the trend towards local foods.
Reference
Wrangham, R. (2009). Catching fire. New York, NY: Basic Books.
Food Processors and Manufacturers
The largest food companies in the US, as of 2007, include:
- Anheuser-Busch
- Tyson
- Dean Foods
- Nestlé
- Kraft
- Cadbury
- ConAgra Foods
- PepsiCo
- General Mills
- Mondelēz
- Smithfield
As a point of reference, Kraft, which recently split into two companies, has joined with Heinz to form KraftHeinz with about 43,000 employees. Mondelēz employs about 100,000 people. So you can see that some of these companies are very large indeed.
Food processors do not get mentioned often in discussions of manufacturing. In Figure 9.4, you can see that food, beverage, and tobacco products are a major source of employment and among the top when it comes to economics. The only segments bigger in terms of dollars in are computers/electronics and chemical products.
Knowledge Check 9.1
Major Food Processors
Now we’ll go through a few examples of the major food processors to give you an idea of how they are structured. Starting with Dean Foods, which is mostly a dairy processor. They contract with dairy farmers to buy their milk, process (pasteurize) it, and then sell it under the name Dean as well as many other brands (See Figure 9.5). The company is based in Dallas but they have a large international presence.
The now called KraftHeinz is a more general food processor. They buy a variety of ingredients to make many different products, like you see in Figure 9.6. Their focus is mostly on US grocery shoppers.
Finally, Tyson Foods is an example of a vertically integrated company and one of the largest meat processors in the world (if not the largest). They own the layers that lay the eggs that become chicks that become broilers (meat chickens) that are processed into fresh/raw meat, and sometimes further processed into other products, such as chicken nuggets. It’s not just chicken! They also do pork and beef products. They sell directly to consumers in grocery stores as well as many restaurants, such a McDonalds, hospitals, and the military. Within the food processing industry, food animal processing is the largest employer.
Though we’ve highlighted some large companies here, many food processors are actually small businesses. Eighty-nine percent of the food processing companies employee less than 100 workers.
Among the 50 states, Pennsylvania is a major food processor. Pennsylvania ranks highly in these food processing industries:
- Canned and frozen fruit and vegetable products (#1)
- Chocolate and cocoa products (#1)
- Potato chips and pretzels (#1)
- Brewing (#6)
- Ice Cream and dairy products
- Egg and meat processing
Food Processing Terminology
As food is processed, it’s transformed from the initial ingredients to the final product. Along the way, many different steps may be taken, including these examples, all called unit operations:
- Cleaning
- Separating
- Size reduction
- Fluid flow
- Mixing
- Heat transfer
- Concentration/drying
- Forming
- Packaging
Altogether, a combination of various unit operations forms the final food. We cannot cover all possible unit operations that are used in food processing. Since food processing has gotten a lot of negative attention in recent years, let’s go through some of these unit operations to see if we can find the source of our anxiety!
Click each unit operation to learn more.
Cleaning
First, let’s consider how food and the environment in which it’s handled are cleaned. Virtually all food is subjected to cleaning before it reaches us, even the most seemingly minimally processed kinds. Remember, food is grown outside! Therefore, we want our food and anything touching our food to be clean. What is the definition of clean and what needs to be cleaned?
To help you appreciate the level of cleaning that is necessary, consider the hand print in Figure 9.9. This is the impression of a child’s hand onto a petri dish. After the petri dish was incubated, all these microorganisms grew! This means that even though your hand may look clean, it’s actually covered with microorganisms, some of which may be capable of causing disease!
By clean we mean on an invisible level, on a microorganism level. Clean from dirt but also from contaminating microorganisms.
Now, you may be saying to yourself, but that was a child’s hand and everyone knows kids aren’t as careful about washing their hands. Look at Figure 9.10. What is this a picture of? Run your tongue over your teeth. Do you feel that fuzzy layer that’s been building up since the last time you brushed your teeth? Those are microorganisms growing in your mouth! And this is a picture of those microorganisms from someone’s mouth!
Companies have to follow Good Manufacturing Practices (GMPs) for cleaning machines and other equipment. They might clean them by hand or they might use another machine to clean. Either way, the important factors are the same as the ones you employ when washing your hands:
- Time
- Activity
- Concentration
- Temperature
- Waste disposal
Food processors go one step beyond cleaning. After a food facility is cleaned such that it looks clean to the naked eye, then it is sanitized to kill microorganisms that cannot be seen. Sort of like when you use bleach to sanitize your kitchen at home.
Separating
Let’s move on to another unit operation. Separation is a step done in the processing of many foods. It can be done based on a variety of factors related to the particular food, including
- Composition
- Size
- Shape
- Density
Some easy to understand examples are removing the husk from grain in order to make flour and separating the cream from milk.
Look at this kernel of wheat, similar to all grains. The kernels have outer coatings that are not digestible (fiber, called husk and bran), a seed (called germ, that would go on to grow a new plant), and the interior endosperm (the white part, full of starch).
During separation in flour milling, rollers are used to squeeze, but not crush, the grains. The friction applied helps to lose and remove the husk.
Video 9.1 shows how the same principles are applied to peel garlic cloves.
Cream is separated from milk based on density. If, after milking the cow, the milk is left to sit, it will naturally separate. The fat in milk (called cream) is less dense than the water and protein in milk, which sink to the bottom.
Size Reduction
Size reduction is another common unit operation. You do this at home when you’re cooking, think of cutting up vegetables into bite size pieces or grinding coffee beans. Size reduction is the principle behind milk homogenization, which prevents the separation that we just talked about.
Sometimes something as simple as processing via size reduction is absolutely vital for the final product. Take, for example, tea. Green tea is essentially the whole tea plant’s leaves simply dried, while black tea is derived from those same leaves but cut up into small pieces and then dried.
There is also size reduction in the flour manufacture process. The endosperm, or starch, has to be crushed into a fine powder in order to make flour.
In the case of milk, size reduction of the fat bubbles in milk will make them stable and no longer float to the top. In this image, milk is pumped at high speed from the left. The large globules of fat are all rushing to try and pass through the small space, so they are forced to form smaller globules which are then stably suspended in the watery part of the milk (See Figure 9.12).
Size reduction is also very common, practically universal, when it comes to meat. Think about how you buy your meat, very few of us buy the entire animal not to mention cook the entire carcass all at once. Rather, we tend to buy different cuts, individual portions, or multiple servings, such as chops or roasts. The pinkish and red that you see in Figure 9.13 is meat or muscle tissue. The white is fat and connective tissue, like ligaments and tendons.
Mixing
When it comes to our concern over food processing, things get sticky when many processes are combined and the final product seems to have little in common with the starting material. Think of a hot dog. Where did an all-beef hot dog come from in relation to the original cow? There is no one muscle or part of the cow that makes up a hot dog. This image of a hot dog versus the cow brings us to a discussion of pink slime. Have you heard of it? It’s the result of a combination of unit operations on meat products.
You see all sorts of commentary on what is in our food circulating the internet. Look at this description of pink slime from one internet site. No wonder there’s concern over food processing!
What they do is take parts of a chicken and put it through this machine that mechanically separate the meat from the bone. Unfortunately, that doesn’t happen. What it does instead is smash EVERYTHING including the bones, eyes and guts making it come out looking like…
Technically speaking pink slime is actually lean, finely textured beef (and beef only, not chicken or pork). What this means is that it’s meat, muscle, that could not be easily cut away from the carcass and so the meat was removed using heat and a machine to do the separation. This results is small bits of meat being recovered. The process of mechanical separation is much more efficient than a human trying to do it. The result, however, are very small pieces of meat that are so small they form a paste, hence the name pink slime. That is why this is only used in ground meat type products (think frozen hamburger patties).
Because pink slime, though perhaps gross, is nothing more than beef and food labeling focuses on food composition, lean, finely textured beef does not have to be declared on food labels. However, given the recent controversy, companies that use lean, finely textured beef, like Cargill, have said they’ll start clarifying it on food labels. Please note that ground beef you get at your local grocery store is usually ground in store from whole muscle cuts and therefore does not contain lean, finely textured beef.
In contrast, mechanically-separated chicken, fish, and turkey have always had to be labeled, and still are, despite confusing messages put out by celebrity chefs such as Jamie Oliver. However you may feel about pink slime and related products, you can avoid consuming it if you wish but it’s a great example of how we try to minimize the amount of food wasted.
Heat Transfer
The transfer of heat is another very commonly used unit operation. We do this at home when cooking all the time, transfer heat from our stoves into our food. In the case of pasteurization, this is a relatively mild heat treatment that comes in the form of various time and temperature combinations. As you know, in any heat exchange, heat flows from the warmer to the colder. In the case of many pasteurizers (See Figure 9.14), such as for milk, the warm pasteurized product is used to warm the incoming cold product (raw milk). This also results in a cooling of the already pasteurized product/milk. This heat recovery is a critical to energy conservation. The heat kills of many microorganisms and thus makes the food safer and last longer. Many foods are required to be pasteurized:
- Milk
- Juice
- Beverages
Canning is a stronger heat treatment, going to a higher temperature for a longer time and including a vacuum seal. The result of this process is a shelf stable food in which all the microorganisms have been killed. These products must be packaged in special containers in order to maintain their sterility, such as cans or pouches.
Concentration and Drying
Removing water from food (drying) is another common process. Water is often removed because it’s heavy, and therefore is expensive to transport. Water removal also increases foods’ shelf-life. Water can be removed in a variety of ways:
- Freeze-drying, for example, works by freezing the food and then reducing the surrounding pressure to make the water frozen inside the food sublimate into gas and drift away.
- Spray drying works by spraying liquid foods into a fine mist, where the water can quickly evaporate away from the tiny droplets leaving behind the solid remnant.
Instant coffee, powdered milk, potato flakes, frozen juice, and canned soup are examples of foods that have had water removed.
Forming
Forming is the second to last unit operation that we’ll discuss. It includes various subcategories, such as compaction, molding, and extrusion. In extrusion, a food dough is forced through a mold to produce often complex shapes. Think of that Play-Doh spaghetti maker you had as a kid! This process may be done with or without a simultaneous heating step. Many foods are extruded, such as the pasta in Figure 9.16.
What other foods can you think of that are formed by extrusion? Click through the image carousel to see examples of common extruded foods.
Packaging
Lastly, packaging. Packaging has a variety of goals:
- Maintain food quality/safety and minimize waste.
- Communicate information to the food consumer.
- Maximize food convenience.
Packaging materials are many and include
- Paper for milk cartons, crackers, cereals
- Metal for canned foods
- Glass for acidic foods like jelly, pickles, juices
- Plastics for milk jugs, cellophane wrapped sandwiches, salads
Paper was once a common method of packaging but it is limited in that it cannot get wet. So paper packages are usually coated in wax. Metal (mostly cans) is another popular choice, especially for shelf-stable foods. See Figure 9.17 to examine a cross section showing how metal cans are sealed. Metal is also relatively easily recycled.
Glass is a wonderful, inert material, so it doesn’t react with acidic foods. But, because it is prone to breaking and is therefore dangerous, it has largely been supplanted by plastic. Plastic is the dominant food packaging material due to its desirable physical properties (light, flexible shape, can be colored, low cost.) Unfortunately, plastics are not easy to recycle as compared to the glass and metal.
To help wrap up our discussion of all the different ways foods are processed, here is a start to finish example of how sugar is grown on the farm, manufactured and packaged. Watch Video 9.2 and describe the basic steps for sugar manufacture (at least three different unit operations) and connect this example of sugar manufacture to at least two other topics that we’ve learned in class thus far.
Finally, let’s conclude this lesson on food processing by looking at some data as to what happens to the nutrients in food as a result of processing. Let’s start by considering this question, is milk a good course of vitamin C?
Most people would say no. If asked what a good source of vitamin C would be, most would say OJ or other fruits. And that’s exactly correct (FYI, vegetables can be a good source too!). Milk is not a significant source of vitamin C in the diet.
Unfortunately, the mild heat treatment of pasteurization can deplete what little vitamin C is in milk. Regardless of the fact that milk didn’t have much vitamin C in it to begin with, raw milk advocates sometimes point to this destruction of vitamin C as a reason to not pasteurize milk, without regard for the case to be made about milk safety. This research article from Science in 1937 shows you how long we’ve been having this debate!
Let’s discuss data from another scientific study, one that looked at various nutrients in peaches before and after the peaches were canned. For our purposes, we will just focus on vitamin E.
In fresh peaches, the amount of vitamin E was 1.24 mg/kg. After the peaches were canned, that number went down a bit to 1.24 mg/kg. Upon sitting in storage for three months, the canned peaches had 1.06 mg/kg. It might seem like the vitamin E concentration continued to go down over time but take a look at the statistics. Statistics are mathematical calculations that help scientists determine if their experimental observations are accurate or not. According to the statistics, the decline in vitamin E between fresh and canned peaches is statistically significant. The decline between canning and sitting for three months is not significant. So, as the peaches continued to sit, the amount of vitamin E was not statistically different and therefore we can say the level was stable over time.
But there’s more to peaches that just vitamin E. Let’s look at vitamin C to see how it was effected by canning. We discover there was not a significant change between fresh and canned, and then again not a significant change after first being canned and sitting for three months. What does this data say about the effect of canning on the nutritional value of peaches?
Let’s discuss another study to see how processing effects other foods. This scientific study compared vegetables processed in a variety of ways. Let’s compare spinach chopped up versus spinach in its whole leaf form. The amount of B-carotene (which becomes vitamin A) is the same in the chopped up version as the whole leaf. But, the liquefied spinach has a value of 1.69, meaning there is more B-carotene available in the liquefied spinach than in the whole leaf version. This is not because putting spinach in a blender somehow created more beta-carotene, rather the act of physically breaking up the spinach helped release the beta-carotene from inside the spinach cells and makes it available for our bodies to digest. It may seem like food processing is destroying the nutrients in foods but sometimes its making them more available!
To summarize these two studies overall, processing caused some nutrients to decrease slightly but others were stable, and others went up! Remember that the numbers shown here are averages. There is a lot of nutrient variation from one piece of fruit/vegetable to the next!
Knowledge Check 9.2
Lesson 9 Activities
Reflection Assignment 4: Unit Operations
Objectives
Here are the objectives for this assignment:
- Identify unit operations used during processing of specific food products.
Relationships to Course Goals
This activity will help students describe and/or identify these examples:
- Common hazards associated with foods and how human behavior affects food safety.
- Techniques (unit operations) used in food processing/manufacture and how they can relate to food preservation.
- Legal and economic constraints on foods, identify the role of different governmental agencies that regulate food production and sale (labeling).
Instructions
- Read all the instructions before beginning! Download and save this file before going on to step 2.
- Before watching the video, review the list of unit operations provided below and refer to your notes/class readings to refresh your memory regarding you’re not familiar with:
- Cleaning
- Separating
- Size reduction
- Fluid flow
- Mixing
- Heat-transfer
- Concentration
- Drying
- Forming
- Packaging
- Preservation related processes (irradiation, canning, pasteurization, etc)
- From the links below, choose and watch ONE video (~5 min).
- How It’s Made—Pre-cooked (frozen) chicken
- How it’s Made—Pringles (chips)
- How it’s Made—Peanut Butter
- How it’s Made—Croissants
- How it’s Made—Beef Jerky
- How It’s Made—Blue Cheese
- How It’s Made—Tofu
- How it’s Made—Gummie Bears (candy)
- After watching the entire video, identify 3 unit operations (see list above) performed during the process (watch the video as many times as necessary to identify the 3). Type your answers to the questions below.
- Food Processing Video selection (1 point)
- Posting date & length (in min:sec, 1 point)
- Identify 3 unit operations observed in the video and briefly describe what happens in each (2 points each).
- First unit op observed
- Second unit op observed
- Third unit op observed
- Reflect on the process you just saw. What surprised you AND what didn’t surprise you about how that food is made? (2 points)
- Finally, save the completed document and upload to the assignment submission area.
Lesson 9 Discussion Forum
Respond to the statements or questions in this discussion forum. Your initial post must be posted by Thursday of the lesson week. Respond to at least two classmate posts by the end of the lesson week. In general, posts should be 50–75 words. Please respond first to posts without replies in order to make sure everyone is included in the discussion.
- In Lesson 2, we watched a video that proposed that cooking food was part of a huge shift in our brain development and contributed to the creation of our species. Richard Wrangham (2009) states, “cooked cuisine was central to the biological and social evolution of humanity.”
- Do you agree with this statement? Use examples and what you learned from previous lessons (or outside sources) to defend your position.
Lesson 9 Quiz
Choose the best answer for each question. You will have 15 minutes to complete the quiz and two attempts. Your highest attempt will be recorded.
Lesson 9 Wrap Up and Looking Ahead
Summary
There is significant evidence that food processing has contributed not only to creating new foods but also to our fundamental development as humans. Many of the industrial processes of today’s food industry are comparable to things we do at home every day when cooking. Food processing is an important industry in the US and Pennsylvania, employing many people. Processing food can have positive and negative effects and we need to be careful to critically evaluate a particular food product before deciding whether its processing was been good or bad.
Check and Double Check
By the end of this lesson, make sure you have completed the readings and activities found in the Lesson 9 Course Schedule.
Ongoing and Looking Ahead
The following lesson will describe one specific food process, fermentation, as well as broaden the discussion to talk about why food spoils, how it can be wasted, and who is most effected by food waste.