Food Processing Operations and Scale-up

Kenneth J. Valentas, J. Peter Clark, Leon Levin

• Publisher: CRC Press
• Year: 2020
• ISBN:
  9781000147568
• Edition: 1
• Topic: Business
• Subtopic: Food Industry
• Index: Business

Intended for students and practitioners who have a basic education in chemical engineering or food science. Contains basic information in each area and describes some of the fundamental ideas of processing development and design. Examines the food industry structure, how it works, consumer products,

1
Introduction

I. Food Process Development

What is process engineering? Process engineering is concerned with feasibility and practicality, that is, will something work and how much will it cost? The “something” in question is usually a process to manufacture a product (food product in this case) at a commercial scale. For any given product, there may be, and usually are, many conceivable methods of manufacture. Typical processes may be capable of manufacturing many different products. Establishing feasibility begins with the conception or selection of promising process candidates.

Since the food industry is oriented toward the retail consumer, in contrast to the oil or petrochemical industries, which have mostly industrial markets, there is a great emphasis on new product development, which generates a need for new processes or new applications of existing ones. This can mean that the first phases of food process development are directed at a purely imaginary product, for which there may not even be a prototype. Further, it may not be possible to have a prototype until a process is conceived.

More common than starting with an imaginary product, process engineering is often directed at scaling up from a bench-top (or kitchen stove) procedure, often first developed by a food scientist, to commercial scale. It is worth considering what commercial scale means in the food industry.

II. Commercial Scale

Many food products are marketed in some form of convenient package or container, such as a carton, bottle, pouch, or other unit. These units range in size from a few ounces (in the case of confections) to several pounds (in the case of milk or soft drinks). A great many products are sold in units of about 1 pound (boxes of breakfast cereal, loaves of bread, cans of fruit and vegetables).

Filling of discrete packages involves a number of separate steps, which are typically performed by mechanical equipment. A number of physical phenomena limit the currently achievable rates of such equipment. Among these limitations are friction, wear, acceleration of fluids, mechanical precision, flow rate of solids, and rates of heat transfer. Overcoming such limitations is one area of opportunity in food process engineering.

As a result of the typical rates achievable currently, commercially available filling equipment operates at rates ranging from 20 to 30 units/min up to 1200 units/min (in the case of high-speed can lines). For the typical 5-day, 2-shift operation of food plants, this gives theoretical production rates of 4.5–270 million units/year, for each filling line. That provides one measure of commercial scale.

Another measurement is financial. Total food sales (excluding restaurants and bulk agricultural commodities) in 1986 were $316.7 billion (3). The largest food companies have annual sales on the order of $10 billion. For these companies, a new product or family of products must have annual sales potential exceeding $100 million in order to represent an interesting opportunity. Not many food products have unit values exceeding $2, though average values are rising as emphasis is placed on greater convenience and higher quality. To achieve $100 million in annual sales, 67 million units (at $1.50 each) must be made. This would require one line operating at 300 units/min, three at 100 units/min, or six at 50 units/min. For high value products, the lower rates are more likely.

Commercial scale then, in the food industry, represents production rates of millions of units per year, scores of units per minute, and tens of millions of dollars in annual value from a typical production line. Multiple lines are common, as are multiple plants for nationally distributed products.

Feasibility is concerned with production of a given product at any rate (initially); scale-up is concerned with production at typical commercial rates when a slower and smaller volume process is known. Scale-up is discussed in some detail elsewhere (Chapter 10); it also is generally amenable to application of fundamental physical principles. Conception of original processes, on the other hand, is treated systematically only rarely. The text by Rudd, Powers and Siirola (9) develops several heuristics, or rules of thumb, for inventing processes.

One purpose of a course or sequence in food process engineering, for which this volume might be used, is to provide the student or practitioner with a vocabulary and grammar for process synthesis in a new area. Extending the analogy to language, this suggests an emphasis on instruction in facts at first, followed by practice with their application. Some of the more relevant facts, and sources for obtaining additional ones, are discussed later. The balance of this book illustrates this approach with specific cases and chapters on certain essential fundamentals.

III. Practicality

Another important aspect of process engineering is practicality, that is, how much does a process cost to build and operate? In conventional chemical engineering, these questions are answered with well-established techniques developed over many years of experience with oil and petrochemical equipment and plants. The arsenal of process equipment types is relatively limited in many chemical plants (heat exchangers, pumps, towers, vessels, reactors, and some others), the principles of operation have come to be well understood and generalized through transport phenomena, and costs have been well correlated with simple measures of their size (8). Few of these conditions currently hold for food process engineering.

Although some food processing equipment is relatively simple (tanks and pumps, for example), much of it is highly specialized and complex. There is surprisingly little commonality among equipment developed for meat processing, baking, and dairies, though all are involved in large food processing segments. Another opportunity for progress in food process engineering would be generalization and simplification of equipment and processes across segments.

Progress has been made in understanding the fundamental principles of many important food process operations, but more remains to be done. The text by Loncin and Merson (6) is one of the best references on such fundamentals. A recent review by Schwartzberg (11) covers most of the available research literature on food process operations. The fact that such a review could even be written is one indication that the literature is relatively sparse.

Finally, food equipment tends to be fairly complex, for a number of reasons, and so correlations of cost with performance characteristics is difficult. It tends to be modular, and so there is little economy of scale, in contrast to much chemical equipment, where decreasing surface to volume ratios contribute to unit cost reductions as size is increased. When a chemical process is increased in rate, it is generally sufficient to make the tanks, reactors, and pumps larger. It requires less metal, all other factors remaining constant, to contain a unit volume as the volume increases. The major contribution to cost of most chemical process equipment is the amount of metal required.

By contrast, when a food process is increased in rate, it often is necessary to provide additional identical units, such as fillers. As a result, unit investment costs tend to be nearly constant, once commercial scale (as previously described) is achieved. In the face of these challenges, determination of food process costs proceeds along a path familiar to well-educated chemical engineers, but probably new to food scientists.

IV. Food Process Design

The approaches taught earliest in the engineering curriculum are among the most useful in food process design, especially heat and material balances. These relatively simple calculations to account for all material and energy flows are basic to process design. About 60–70% of the cost of most food products is the cost of raw materials, so yield improvement and proper accounting are critical to the efficient design and operation of food processes. Some yields can be surprising: It takes about 10 pounds of milk to make 1 pound of cheese; about 1-half the weight of a hog or steer is edible by humans; about one-half of the weight of an orange is juice.

Despite its importance, obvious to most engineers, preparation of an accurate material balance is not common in the food industry. Clearly, it should be. One complication is that many food processes are batch rather than continuous. Often batch and continuous operations are combined. This can lead to some conceptual and calculational challenges, because batch processing tends to be ignored in the typical engineering curriculum. At Purdue, Reklaitis, Okos, and their students (7,12,13) have done research on batch and semi-continuous process simulation, including some food examples.

Energy balances, likewise, are important, not because energy is a large cost in food processing, though it can be significant, but because correct application of energy may be the essence of a food process. Such important and unique processes as sterilization, pasteurization, freezing, drying, evaporation, baking, cooking, blanching, and frying all involve the addition or removal of heat to or from foods. Precise delivery of the correct amount of energy is important because both too much and too little can be harmful.

Because of the relative lack of known fundamental principles, physical properties, and rate constants, much food equipment sizing is done empirically, relying on experience or experiment. Rarely is experimentation as systematic as it could be, because the complexities appear overwhelming. It is important not to be overwhelmed in such cases, but rather to apply the statistical principles of experimental design and to focus on the critical parameters needed for process design, which tend to be related to rates of heat transfer, material flow, and biochemical reactions. There is an understandable tendency in much food process research to concentrate on the manufacture of edible product instead of useful data. This tendency arises from a confusion between the missions of process research and product development.

It has been said that the last thing one should do in studying baking is to bake bread. That does not mean never actually baking; rather, it means using model systems first to characterize heat transfer, learning the physical and chemical properties of dough, and developing mathematical models of heat and mass transfer in a system where geometry, weight, and properties all change with conditions and time. Then, bake bread to confirm the model.

In general, the development of a mathematical model is a good goal for food process development. Such a model provides a framework and a guide for research, serves as a useful tool for design once developed, and can demonstrate (by its relative success) the degree of understanding achieved. Relatively few food processes have been adequately modeled in this sense, certainly by comparison to other industries, and so such efforts represent another opportunity for progress in food process engineering.

V. Illustrative Cases

The food industry is very diverse, but it can be explored by sampling the major segments, as defined by the U.S. government in its Standard Industrial Classification (SIC). Table 1 lists the major segments in SIC 20, Food and Kindred Products. Four-digit SIC codes define more specific products within these broad segments. There are 47 four-digit codes currently in use. In contrast, there are 28 four-digit codes for SIC 28, Chemicals and Applied Products (14).

TABLE 1 Major Segments of SIC 20 Food

201.	Meat and poultry products
202.	Dairy products
203.	Canning and preserving fruits and vegetables
204.	Grain mill products
205.	Bakery products
206.	Sugar and confections
207.	Fats and oils
208.	Beverages
209.	Miscellaneous and kindred products (seafood, pasta, etc.).

This volume includes relatively detailed descriptions of cases taken from several segments that are meant to provide a framework for further exploration in class or individual study. It is not meant to be a definitive reference for any process; such information sources abound in the patent literature and other texts. Information used here has been taken from such publicly...

Table of contents

• Cover
• Half Title
• Series Page
• Title Page
• Copyright Page
• Preface
• Table of Contents
• 1 Introduction
• 2 Overview of the Food Industry
• 3 Financial Analysis of Capital Projects
• 4 Food Chemistry
• 5 Soy Complex
• 6 Ready-to-Eat Breakfast Cereals
• 7 Dairy Products
• 8 Orange Juice Case Study
• 9 Food Product Development
• 10 Scale-Up of Food Processes
• 11 Dimensional Analysis
• Index