The Role of Steam in the Food Processing Industry

Steam plays a pivotal role in the food processing industry, combining efficiency with versatility to meet the demands of modern food production. Its applications span cooking, sterilization, pasteurization, and dehydration, ensuring that food products are safe, nutritious, and of high quality.

One of the most significant uses of steam is in cooking. Steam cooking offers even heat distribution, which helps retain the texture, flavor, and nutritional value of food. Unlike frying or baking, which can degrade nutrients, steaming is particularly beneficial for preparing vegetables, seafood, and grains, providing a healthier alternative. Advances in steam cooking technology, such as pressurized steam systems, have further improved cooking efficiency and consistency in industrial settings.

Steam is equally essential in sterilization and pasteurization processes, both critical for food safety. Sterilization involves using high-temperature steam to eliminate harmful microorganisms from food, equipment, and packaging materials. This ensures a safe production environment and extends the shelf life of food products. For pasteurization, steam heats food to precise temperatures for controlled periods to destroy pathogens while preserving sensory and nutritional properties. This technique is widely used for dairy products, beverages, and ready-to-eat meals, meeting regulatory standards and consumer expectations.

In dehydration, steam plays a supporting role in removing moisture from food to prevent spoilage and reduce bulk for storage and transportation. Techniques like steam-assisted freeze-drying are employed for high-value foods, such as fruits and spices, to maintain flavor and color while achieving extended shelf life.

The food industry is also leveraging innovations in steam technology to reduce energy consumption and enhance sustainability. For example, steam recycling systems recover and reuse waste steam, cutting operational costs and lowering environmental impact. These advancements align with global efforts to promote eco-friendly manufacturing practices.

In conclusion, steam's unparalleled efficiency and adaptability make it indispensable in the food processing industry. From preserving nutritional integrity to ensuring safety and sustainability, steam is a cornerstone of modern food production, meeting the growing demand for high-quality and safe food products worldwide.
The Role of Steam in the Food Processing Industry

Advantages and Applications of Infrared Heating

Infrared (IR) energy, a ubiquitous natural phenomenon, is integral to various heating applications. IR heating leverages both radiative and conductive heat transfer to generate and disseminate warmth efficiently. Unlike other heating methods, IR radiation primarily heats the surface of objects, penetrating only a few millimeters into food. This surface-level absorption allows the energy to be subsequently conducted throughout the food, ensuring uniform heating.

Occupying a segment of the electromagnetic spectrum between visible light and microwaves, IR wavelengths range from 0.5 to 100 µm. This range includes near-infrared, mid-infrared, and far-infrared, each with distinct heating characteristics suitable for different applications. For instance, near-infrared is often used in industrial drying processes, while far-infrared is favored for therapeutic and residential heating solutions.

IR heating offers several advantages over traditional methods. It significantly reduces heating time and energy consumption, which is crucial for both environmental sustainability and cost-efficiency. Moreover, IR heating ensures uniformity, minimizing quality degradation and preventing solute migration within food materials. The equipment used for IR heating is typically more versatile, compact, and straightforward compared to conventional systems.

Recent advancements in IR technology have further optimized its application in various fields, from enhancing food processing techniques to improving residential heating systems, making it a valuable and energy-efficient heating solution in modern technology.
Advantages and Applications of Infrared Heating

Fruit canning

Food is preserved by using methods that destroy or hinder the growth of microorganisms, such as molds, yeast and bacteria. These organisms may be present in the soil, on the food, in the air, on equipment or on work surfaces.

Yeasts, molds and bacteria must be destroyed during processing to prevent the food from spoiling. The correct amount of time to process varies with the kind of food. Sufficient heat for a specified length of time kills microorganisms and insures a safe product.

Canning is a method of preserving food by first sealing it in air-tight jars, cans or pouches, and then heating it to a temperature that destroys contaminating microorganisms that can either be of health or spoilage concern because of the danger posed by several spore-forming thermo-resistant microorganisms, such as Clostridium botulinum (the causative agent of botulism).

Canning is also to retain nutrients and optimum quality, preserve fruits and vegetables when at their peak of freshness. All fruit preserved by canning should be heat-processed to attain commercial sterility.

Whereas vegetables and certain other foods require the application of high temperature (240°F, 250°F) or higher for significance lengths of time to attain commercial sterility, most fruits sufficiently acid (PH usually below 4.5) that commercial sterility can be attained by heating the containers in boiling water to the point where all parts of the product reach a temperature of 180°F – 200°F.

After heat sterilization, containers are quickly cooled to prevent overcooking. Containers may be quick cooled by adding water to the cooker under air pressure or by conveying the containers from the cooker to a rotary cooler equipped with a cold-water spray.

Adding syrup to canned fruit helps to retain its flavor, color, and shape. It does not prevent spoilage of these foods.
Fruit canning

Radio frequency heating in food process

Radio frequency (RF) and microwave (MW) are electromagnetic (EM) waves. In RF and MW heating, which are also called dielectric heating or dielectric loss heating, heat is generated within the products by molecular friction in high-frequency alternating electric fields.

In very simple terms, radio frequency heating of foods arises from the direct conversion of electrical energy to heat within the volume of the food itself. With an electric field alternating at the 27.12 MHz radio frequency, the electric field alternates 27, 120, 000 cycles per second. The energy release resulting from the movement of the molecules and the space charge is displacement causes the material to rapidly heat throughout.

The rapid heating method of RF offers considerable advantages over conventional slow heating processes, rendering significant applications in different food products. The physical factors such as shape, geometry and product position, as well as dielectric properties, are the fundamental factors that affect the RF heating systems.
Radio frequency heating in food process

Microwave processing of foods

Microwave ovens are mainly used for heating and reheating of foods; however, trends show that they are used increasingly also for cooking and defrosting.

Industrial scale microwave processing units have been developed for drying, precooking of meat, pasteurization of ready meals, and tempering of meat and fish. Microwave processing is generally characterized by uniform heating on a macroscopic scale and rapid heating rates, as opposed to conventional processing.

Microwave heating talks place throughout the volume of the product. This volumetric heat delivery leads to a much higher rate of heating than conventional methods, limited by the heat penetration from the heated surface to the bulk of the material.

Microwave processing is used in various industrial application:
*Pasteurization of liquid and viscous in the food industry
*Sterilization of liquid products on food/pharmaceutical sector
*Drying of casings in sausage production
*Heating of minced meat mixtures after the extruder for flashing
*Preheating of viscous products before spray dryers or vacuum dryers
Microwave processing of foods 

Canning of strawberry fruit

The steps in canning strawberry are the following:
Strawberries for canning purposes should be firm in texture, of good color and flavour and of large size

Strawberries left alone for a couple of hours with sugar added to them will create their own syrup. An important item in canning the strawberry is to have them thoroughly heated before putting in cans, and the sooner they are sealed after being sufficiently heated the better they retain their color and flavor.

Prepare heavy syrup of 50° Brix. Fairly heavy syrup is necessary to develop and retain the berry flavor

Fill canning jars with berries within 1/2 inch of the top. Add just enough syrup to cover the berries. Place any remaining syrup in its own canning jar and fill to the same level

Strawberries are not suitable as fruit preserve in syrup than as canned fruit. When preserving strawberries in syrup, a glass jar is more convenient.
Canning of strawberry fruit

Steam infusion heat exchanger

Direct heating involves direct contact between the food and the heating medium by steam injection or steam infusion.

Steam injection introduced steam into the product of an injection chamber as product is pumped through the chamber, while steam infusion introduces product through a steam-filled infusion chamber.

A steam infusion heat exchanger provides a direct contact between steam and the product. A product in liquid state is pumped to the top of the heat exchanger and then allowed to flow in thin sheets in the heating chamber.

It is heated to 142 – 146 ° C in 0.3 seconds and is held for 3 seconds in a holding tube before flash cooling in a vacuum chamber to 65 -70 ° C.

The flash cooler has dual purposes. First, it reduces the sterilization temperature in a very short time and second, it removes water from the product.

The viscosity of the liquid determines the size of the spreader. Products containing particulates, such as diced vegetables, meat chunks and rice can be handled by specially designed spreaders.

High rates of heat transfer are archived when steam contacts tiny droplets of the food. The temperature of the product rises rapidly due to steam condensation.

Steam infusion has advantages over injection methods because the liquid does not contact hotter surfaces and burning-on is therefore reduced.
Steam infusion heat exchanger

Infrared heating in food processing

Thermal processing of foods is very important in extending the shelf life of various food products. Infrared heating was first used in the 1930s for automotive curing applications and rapidly became a widely applied technology in various industrial fields such as sensing, measuring, analysis, communication and heat treatment.

Infrared radiation is the part of the electromagnetic spectrum that is predominantly responsible for the heating effect of sunlight.

The infrared spectrum of radiation can be divided into three different categories:
Near-infrared radiation (wavelength: 0.75-3 μm)
Mid-infrared radiation (wavelength: 3-25 μm)
Far-infrared radiation (wavelength: 25 - 1000 μm)

Infrared heating in food processing had been applied in such as drying, dehydration, blanching, thawing, pasteurization, sterilization, and other miscellaneous food appliances such as roasting, frying, broiling, and cooking as well as in-depth assessment of pathogen inactivation.

Infrared technologies in the food processing sector have an attractive merit such as uniform heating, high heat transfer rate, reduced processing time, and energy consumption and improved product quality and safety.
Infrared heating in food processing

Process of microwaving the food

The absorption of microwave by a dielectric material results in the microwaves giving up their energy to the materials with a consequential rise in temperature. Food composition (mainly water content) is a key factor that determines how fast it will heat in a microwave environment.

Cooking food using a microwave oven is accomplished by setting an appropriate amount of time necessary for the waves to penetrate the food and cook it.

The most important advantages of microwave heating is that microwaves are capable of penetrating very deeply into certain materials heating extend within the entire food material, which result in very significant reductions in process heating times for drying, thawing, sterilization and so on.

There are limits to the depth of their penetration. The geometry of the food to be heated is an important consideration; conduction and convection may often take far longer to heat a given mass of food.

Microwaves generate heat due to their interactions with the food materials. The microwave radiation itself is non-ionizing radiation, distinctly different from ionizing radiation such as X-rays and gamma rays.

Heating foods evenly in a microwave oven is difficult at best, particularly with solid foods of different composition.

A major use of microwaves in the food industry is the tempering and thawing of frozen foods, especially meat, fish, butter and fruit.
Process of microwaving the food

Tea leaves drying process

Drying achieved by blowing hot air through tea leaves, arrests oxidation by inactivating enzymes, resulting in color enhancement and the final balance of tea aroma and reduces the moisture content of the leaves to less than5%.

In Keemun black tea processing, the leaves are subjected to drying after fermentation at 110 °C– 120 °C for 10 – 15 min. The moisture will drop below 20%.

After spreading the first dried leaves, another drying is carried out at 70 °C – 90°C for 45 –60 min to moisture below 4%.

Drying is usually done by a drying machine such as the multi-band drier or fluid bed drier.

The temperature is sufficient to inactivate the polyphenol oxidases. The sap released during rolling and fermentation solidifies during drying on the fine little hair on the surface of the leaf.

During drying, aroma substances are formed and the coppery-red color is changed to black (hence ‘black tea’).

Following the drying the leaves are sorted and graded to yield a commercial product.
Tea leaves drying process 

Ricotta cheese processing

Like cottage cheese, ricotta cheese is a high moisture cheese. Its composition varies depending in whether it is made exclusively from whey or from a blend of whey and milk. Ricotta can be used in many of the same ways a cottage cheese. It is especially popular as an ingredient in Italian cuisine.

It was first made in Italy and therefore is classed as an Italian cheese. The basis of traditional ricotta manufacturing process is the coagulation of whey proteins by heat. The usual raw material is whey from cheddar, Swiss, Mozzarella or other hard cheese. . Ricotta cheese is now prepared from whole milk with or without addition of whey.

Most of the ricotta production is confined to a batch process. It is common to blend 10-25% milk to neutralize acid in the whey, enhance yield and curd cohesiveness. The mixture is heated in a kettle to 82-93 °C, followed by the addition of a food –grade acid such as lactic, acetic or citric acids in quantity enough to drop the pH of the mixture to 5.9 – 6.1.

Vinegar, citric acid solution or sour whey may be used as an acidulant for sweet wheys.

The mixture is held for 15-20 min, after which the curd is dipped with a perforated ladle and collected in a muslin bag.

The bag is allowed to drip and cool in cold temperature. Alternatively, the curd is drained in perforated stainless hoops and allowed to dry. Salt and lactic starter bacteria may incorprrated into the draining curd and it has cooled to 30 ° C. Lactic acid starter is to improved the flavor and promote ripening,

The dried curd may be packaged into plastic bags or cups for marketing as ‘fresh’ ricotta, or it may pressed to produce dry ricotta.

The curd is soft, fragile and grainy, and may be pressed slightly to achieve cohesiveness. If it is to be marketed as fresh or moist, draining is continued or the curd may be pressed for several hours in cheesecloth-lined hoops, then it is packed in paper cartons that usually hold 5 pounds.

Ricotta produced by the traditional method is very susceptible to spillage by yeasts, molds, and bacteria and hence has a relatively short shelf-life 1 to 3 weeks at 4 °C.

Significant advances have been made in the automation of ricotta cheese production with the objective of improving curd separation, cheese yield and shelf life.
Ricotta cheese processing

Processing of Honey

Processing of Honey
The processing of honey may be very simple e.g. in the case of a hobby operation, or extremely complex involving a great deal of technology tailored to each individual honey type.

Most processing however is concerned with liquefying and straining (or filtering) honey.

Both of these operations usually require some application of heat to the honey. The heat has the dual effect of removing crystallization in natural honey, and to reduce the viscosity.

Both of these things are required to provide a product that can be cleaned and further processed for creamed honey or just filled into jars as liquid honey.
Processing of Honey

Drum dryer operation

The drum dryer is a continuous contact dryer widely used in the food industry for drying products initially in liquid form.

It is highly flexible equipment consists of one or two horizontally mounted hollow cylinders made of high-grade casts iron or stainless steel, a supporting, a product feeding system, a scrapper and auxiliaries.

The variety of feed arrangements available ensures that solution, suspension and pastes with a wide range of viscosities can be dried.

In drum drying, a thick film of feedstock is applied to the external surface of a heated drum which rotates slowly about its horizontal axis.

The feed can be pre-concentrated and preheated to reduce the drying load but there is a limit to the feed concentration beyond which the sheet may not form well.

In operation steam at temperature up to 200 °C heats the inner surface do the drum. The moist material is uniformly applied in a thin layer (0.5 - 2mm) onto the outer drum surface.

The layer of material remains attached to the drum for about 80% of a revolution drum which time moisture evaporates and leaves behind a layer of solids, which is subsequently removed from the drum surface by a scrapper or doctor knife.

There are many types of drum dryer available:
*Atmospheric double drum dryers
*Atmospheric single drum dryers
*Atmospheric twin drum dryers
*Enclosed drum dryers
*Vacuum Double drum dryers

The single-drum comprises only one roll. A double drum dryer comprises two rolls, which rotate toward each other at the top.

By using the drum dryer, the products have a good porosity and hence good rehydration due to boiling evaporation.

Drum dryers also can dry viscous foods, such as pastes and gelatinized or cooked starch, which cannot be easily dried with other methods.
Drum dryer operation

Heating in food processing

Heat Processing
The development of the modern eating process started in France during the first decade of the 1800s by Nicholas Appert who preserved foods in sealed glass jars in boiling water

In 1819, William Underwood of the United States started the first canning factory in Baltimore.

But to preserve foods in boiling water took too long, requiring about 6 hours, so salt was added to the water bath which increased the boiling temperature, thereby shortening the processing time.

However salt corroded the cans so the next innovation was to heat in steam under pressure. The higher the pressure, the higher the temperature and the shorter the processing time.

These early pressure chambers evolved into the modern retort.
Heat Processing

Preservation of Foods by Heat: The History

Preservation of Foods by Heat: The History
Preservation of foods by heat may be considered as the first invented of preservation technology.

The origins of drying and chemical preservation by alcohol or acid (generated by fermentation) have been lost in history as is the use of ice.

Nicholas Appert, in the late 1700s, applied heat to acid and low acid foods sealed in bottles and eventually received a prize of 12,000 French francs from the French government or inventing a method for safety preserving foods for long term storage.

Appert established a food preservation business in 1812. Peter Durand in England, in the early 1800s, adopted Appert’s process to foods packed in tin coated steel canisters.

While the canisters were hand make, heating of foods in hermetically sealed, tinned steel containers, formed the basis for the first true manufacturing of acid and low acid convenience food products.

The tin can made heat preservation practical as metal containers were more compatible with package filling, sealing, heat processing and the subsequent rigors of storage and distribution.

Early heat preservation technology was constrained by the misconception that air caused food spoilage and by the lack of safe, reliable and properly instrumented steam pressure retorts.

Appert attributes his success at preserving foods by heat to the excellent packaging he developed using glass bottles of his own specification and his carefully prepared stoppers made from hand-cut and glued cork.

He assumed that air was responsible for the spoilage of food. His meticulous procedures for filling and sealing his glass bottles reflect this belief.

Appert was limited to boiling water baths for preservation and heating times were in the order of hours for some products.

Appert’s successor, his son, Raymond Chevallier Appert, adapted the steam autoclave so that packaged foods could be heated above 100 degree C.

The higher temperature allowed shorter heat treatment. Raymond Chevallier Appert could be considered among the first food engineers as he invented a manometer which allowed him to control steam pressure to provide temperatures accurate to 1 degree C.
Preservation of Foods by Heat: The History

Milk Processing: Flavor Treatment

Milk Processing: Flavor Treatment
Milk is usually given what is called a flavor treatment to provide a product that is uniform in odor and taste.

During flavor treatment, milk is instantly heated to about 195 degree F (90.6 degree C) with live steam (injected directly into the product) after which it is subjected to a vacuum of about 10 in. (25.4 cm) in one chamber and to a vacuum of about 22 in. (55.9 cm) in another chamber.

The high vacuum treatment serves to regulate flavor, to cool the milk to about 150 degree F (65.6 degree C) and to evaporate water that may have been added through the injection of steam.

While the milk is still hot, it is usually homogenized by passing it through a small orifice that breaks up the fat globules to a small size, preventing the separation of cream from the milk.

The milk is then quickly cooled to about 35 degree F (1.7 degree C). This is done by the same general procedure used in heating, except that refrigerated water or brine, or directly expanded ammonia is used in the coils, vat jacket, outer tubes of the pasteurizer.

During HTST (high temperature short time) pasteurization and during flavor treatment and homogenization, milk is passed through the heating and cooling cycles at such a rapid rate that at no time is it held for long periods at high temperature.

After processing and cooling, milk is filled mechanically into containers, made of waxed or plastic-coated cardboard of different volumes up to 2 qt and of semi-rigid plastic containers of 2 qt. or 1 gal and the containers are sealed.

In this state, milk should be held as close to 32 degree F as possible until consumed.
Milk Processing: Flavor Treatment

Microwave in food processing

Microwave in food processing
Microwave and radio frequency heating refers to the use of electromagnetic waves of certain frequencies to generate heat in a material.

Typically, microwave food processing uses the 2 frequencies of 2450 and 915 MHz. Of these two, the 2450 MHz frequency is used for home ovens, and both are used in industrial heating. It is worthwhile to note that outside of the United States, frequencies of 433.92, 896 and 2375 MHz are also used.

There is not much commercial use of these frequencies for food pasteurization or sterilization, although they are used in baking and other processes in the food industry.

Heating with microwave and radio frequency involves primarily 2 mechanisms-- dielectric and ionic. Water in the food is often the primary component responsible for dielectric heating.

Due to their dipolar nature, water molecules try to follow the electric field associated with electromagnetic radiation as it oscillates at the very high frequencies. Such oscillations of the water molecules produce heat.

The second major mechanism of heating with microwaves and radio frequency is through the oscillatory migration of ions in the food that generates heat under the influence of the oscillating electric field.

Microwave and radio frequency heating for pasteurization and sterilization are preferred to the conventional heating for the primary reason that they are rapid and therefore require less time to come up to the desired process temperature.

This is particularly true for solid and semi-solid foods that depend on the slow thermal diffusion process in conventional heating. They can approach the benefits of high temperature-short time processing whereby bacterial destruction is achieved, but thermal degradation of the desired components is reduced.
Microwave in food processing