Etiket Arşivleri: Canning

Canning – A Preservation Process ( AKANKSHA DIXIT )

What is Canning? 

Canning is a method of preservation of food in which the food is processed and hermetically sealed in containers (of metal, glass, thermo stable plastic, or a multi-layered flexible pouch) through agency of heat.

Canning provides a shelf life typically ranging from one to five years, although under specific circumstances it can be much longer.

Heating is the principle factor to destroy the microorganisms and the permanent sealing is to prevent re-infection.

Why is Canning done?

The high percentage of water in most fresh foods makes them very perishable. They spoil or lose their quality for several reasons.

Microorganisms live and multiply quickly on the surfaces of fresh food and on the inside of bruised, insect damaged, and diseased food. Oxygen and enzymes are present throughout fresh food tissues. Proper canning practices minimize the effects of these microorganisms.

However, the main objective of canning is to preserve the food by the application of heat so that it can be safely eaten at a later time. Safety of the consumer is the primary concern when food is canned.


During the first years of the Napoleonic wars, the French government offered a hefty cash award of 12,000 francs to any inventor who could devise a cheap and effective method of preserving large amounts of food. The larger armies of the period required increased and regular supplies of quality food. In 1809, Nicolas Appert , a French confectioner and brewer, observed that food cooked inside a jar did not spoil unless the seals leaked, and developed a method of sealing food in glass jars which was referred to as APPERTIZATION and now known as CANNING.

Foods that are canned:

(a) Low acid foods: Meat, fish, poultry, dairy fall into a pH range of 5.0 to 6.8. This large group is commonly referred to as the low acid group.

(b) Acid foods: With pH values between 4.5 and 3.7. Fruits such as pear, oranges, apricots and tomatoes fall in this class.

(c) High acid foods: Such as pickled products and fermented foods. The pH values range from 3.7 down to 2.3, also Jams and Jellies are in this classification.

Commercial Canning Operations


Shelf-stable foods go through various operations before making them ready for marketing, distribution, and consumption. Some typical operations in the commercial canning process are schematically represented in Figure 3.15.


The quality of processed foods depends largely on the quality of the incoming raw product, which in turn depends on how the food is procured or harvested, handled, and stored. Harvesting at the proper maturity is an important step in thermal processing of fruits and vegetables.

Most fruits are harvested and processed in the “softripe” stage. Exceptions include bananas, pears, and some apples, which, when harvested at a mature stage, produce a higher quality processed product than those harvested at the “soft-ripe” stage.

Vegetables; for freezing preservation are generally harvested at a tender stage, while for canning they are harvested at a somewhat more mature stage so they will have sufficient strength to withstand the cooking required for achieving commercial sterilization.

With meat and fish, this refers to postmortem or post-catch quality, in which case the slaughtering and catching practices – and subsequent storage conditions – will affect the raw material quality. Raw material selection is the first step in the process for the implementation of quality control and quality assurance concepts, including the application of hazard analysis critical control point (HACCP) approaches.


The purpose of cleaning is to remove undesirable foreign material and should be designed to obtain:

– maximum separation efficiency consistent with minimum wastage of good material;

– complete removal of separated contaminants and avoidance of recontamination;

– a clean product surface in an acceptable condition;

– minimum quantity and concentrations of residues.

The foreign material found on fruits and vegetables can be grouped under the following headings:

Mineral: soil, sand, stones, metallic particles;

Plant: twigs; foliage, stalks, pits, skins, husks, rope, and string;

Animal: excreta, hair, insect eggs, body parts;

Chemical: spray residues, fertilizers;

Microbial: microorganisms and their by-products

Cleaning Methods

There are two basic types – dry and wet – that are usually used in combination.

Dry Cleaning Methods

The main dry cleaning methods are based on screens, aspiration, or magnetic separations.

Dry methods are generally less expensive than wet methods and the effluent is cheaper to dispose of, but they tend to be less effective in terms of cleaning efficiency. A major problem is recontamination of the material with dust.

Precautions may be necessary to avoid the risk of dust explosions

Screens Screens are essentially size separators based on perforated beds or wire mesh by which larger contaminants are removed from smaller food items (e.g., straw from cereal grains, or pods and twigs from peas). This is termed ‘‘scalping’’ (Figure 1.1a). Alternatively ‘‘de-dusting’’ is the removal of smaller particles (e.g., sand or dust) from larger food units (Figure 1.1b).

The main geometries are rotary drums (also known as reels or trommels) and flatbed designs. Some examples are shown in Figure 1.2.

Cleaning by abrasion between food particles or between the food and moving parts of cleaning machinery is used to loosen and to remove adhering contaminants. Trammels, tumblers, vibrators, abrasive discs, and rotating brushes are used for this purpose

Aspiration This exploits the differences in aerodynamic properties of the food and the contaminants. It is widely used in the cleaning of cereals, but is also incorporated into equipment for cleaning peas and beans. The principle is to feed the raw material into a carefully controlled upward air stream. Denser material will fall, while lighter material will be blown away depending on the terminal velocity

Magnetic cleaning is designed to detect and remove metallic contaminants that can damage preparatory equipment from the raw products. Rotating or stationary magnetic drums, magnetized belts, magnets located over belts carrying the food or staggered magnetized grids, through which the food is passed, are used involving permanent and electromagnets

Wet Cleaning (Washing)

Wet cleaning is effective in removing firmly adhering soils. The addition of detergents and sanitizers can greatly improve cleaning efficacy. However, there are disadvantages. The large amounts of water used subsequently produce a considerable volume (15,000 L/metric ton of canned food) of highly polluting effluent that requires expensive waste treatment. The resulting wet surfaces can spoil more rapidly and may require dewatering to provide clean material suitable for processing or storage.

Passive soaking is the simplest wet cleaning method. It is often used as a preliminary stage in the cleaning of root vegetables heavily contaminated with adhering soil. The soil is softened and partly removed along with stones, sand, and other abrasive materials.

The cleaning efficiency is improved by agitation via caged propeller stirrers built into the tank, by slow-moving paddles, or by a horizontal perforated rotating drum partially submerged in the soak tank.

While warm water improves the soaking efficiency it can induce increased microbial growth and spoilage.

The use of detergents is increasing, especially in foods contaminated with spray residues and mineral oil. These must be selected with care as they may affect the appearance and texture of the food. For example, sodium hexametaphosphate has a softening effect on peas, and some metal ions, such as calcium, can increase toughness.


Green Pea Canning



Canning, the process of placing foods in jars or cans and heating properly to a specified temperature, is a way to preserve many different foods. The high heat destroys microorganisms and inactivates enzymes to preserve the safety and quality of the food. Peas are legume vegetables cultivated for the fresh green seeds, tender green pods, dried seeds and foliage. Peas lose their sweetness and delicate flavor as they mature. Those of the best quality are young, fresh, tender and sweet. This underrated vegetable is rich in assorted vitamins and minerals, high in antioxidants and phytonutrients, and low in fat and calories.

Recipe and Directions

Selecting Peas

The most important step!
Choose only fresh, young, tender peas.

Harvesting :

Peas are of the best quality when they are fully expanded but immature, before they become hard and starchy. Peas should be picked immediately before cooking because their quality, especially sweetness (like that of sweet corn), deteriorates rapidly.

Tenderometer (maturometer):

this method is based on the fact that unripe peas are more tender than ripe peas. thus, ripe peas give a higher resistance than unripe peas when they are sheared between two grids , or penetrated by a series of steel pins.

Canned Meat

1. Introduction

Canning is basicaly a heat processing operation where heat flows from a hot body to a cold body.Among the various methods of extending meat shelf life, canning has the adventage of keeping as much as possible of the original chemical, physical, and sensory characteristics of meat. In addition, canning allows storing and transporting meat, a highly perishable material, in experiments where no other preservation method is succesful. Canning is especially appropriate for meats marketed to tropical conditions, where temperature and humidity are high.

The aim of canning is to destroy microbial populations and/or enzymes responsible for meat deteriorations.In 1810, Peter Duran and Thomas Saddinton in England first commercially applied canning technology to extend meat shelf life by placing it into sealed containers and heating them thoruoghly. However, earlier efforts to preserve food materials by this method were made by Nicholas Appert in France in 1790.

2. Microbial Destruction by Heating

In activation of pathogens and spoilage microorganism by heat is calculated from the point of view of shelf life extension as well as by alteration of sensory characteristics.

Depending of microbial species, vegetative cells of bacteria and fungi can be destroyed when heated at 60˚ C to 90˚ C. Inactivation of bacterial spores require temperature between 115˚C and 121˚ C. In activation of meat enzymes occurs in most cases at 60˚ C to 75˚ C

The process also ensures sanitary conditions, destroying this respect to two bacteriological problems to be solved by canning are as follow:

1. Elimination of vegetative cells and spores that can grow and produce toxins

2. Elimination or inhibition of the development of spoilage microorganisms

During heat treatment, the main problems related to microbial populations are as follow:

1. All microorganisms fisible to grow and produce toxins must be eliminated. Canned meat must be free of Clostridium botulinum, which is most dangerous and produce a fairly heat-stable toxin

2. Spoilage microorganisms must be reduced to a safe limit. Any canned food is sterile if it is free of spoilage microorganisms such as Cl. perfingens. Spore forming thermophiles such as Cl. sporogenes must be considered only when storage temperatures are high.

Heat treatment severe enough destroy Cl. botulinum or Cl. perfingens gives as a result a stable food without the need for applying further preservation methods. However, because severe heating can alter sensory characteristics, it is necessary to achieve a compromise between preservation and alteration of sensory attributes. It is important to note that heat treatment can also improve sensory characteristics of meat, such as texture and flavor.

Thermal resistance of microorganisms increases because of the following factors:

1. pH and water

2. Fat, carbohydrate, protein, and salt content

3. Presence of other microbial inhibitors

Meat, in general, has low acidity (>4.5), with the exception of fermented meats. In this case, preservation achieved by acid production of lactic acid bacteria. Acids of chemical origin also acts as antimicrobial agents. In this case meats require mild heat treatment. In low acid or ph neutral foods, such as most canned meats, stronger heat treatments needed because potential pathogens or spoilage microorganisms can grow.

3. Commercial Heat Treatments

Vegetative cells are destroyed at temperatures slightly higher than their maximum growth temperature, whereas spores can survive at much higher temperatures.

Basically there are four heating process applied to food materiels, based on temperature increase.

1. Blanching

2. Cooking

3. Pasteurization

4. Sterilization

3.1. Blanching

Blanching is applied to inactivate enzymes in products receiving further heat treatments. For meats, volume reduction usually occurs. It is also used to eliminate gas from the tissues or simply to provide an initial cleaning of the food material. Blanching temperatures around 65˚ C.

3.2. Cooking

Cooking is applied to improve sensory characteristics of tho food material, although it also destroys a number of microorganisms and inactivates some enzymes. It takes place at around 85˚ C.

3.3. Pasteurization

Pasteurization destroys pathogenic vegetative cells, but certain heat resistant microorganismms and spores can survive. Pasteurization temperatures are 140 C to 150˚ C for 1 to 45 seconds, or 70˚ C to 73˚ C for 15 to 20 seconds.

3.4. Sterilization

Sterilization destroy vegetative cells as well as spores; the shelf life of sterilized foods is considerably extended even without the application of additional preservation methods. Time-temperature relationship of the sterilization process depends on thermal resistance of a given microorganism, taken as spoilage indicator.

4. Meat Canning Process

Meat canning consist of several steps, although the basic principle is heat treatment of a sealed container. Once the meat and other ingredients are prepared, canning basically includes three main operations:

1. Can filling

2. Exhausting and closing

3. Sterilization treatment

Can Filling

When a solid material canned together with a liquid, heat penetration is affected by the solid-liquid ratio as well as the solid distribution within the can. Solid material packed loosely is heated faster than closely packed material.

In general, 30% of the can volume must be liquid (brine or sauce) in order to have a good heat transfer. Liquid is always filled after solids. In order to calculate heat tranfer, headspace must be always taken into consideration.

Exhausting and Closing

Exhausting efficiency depends largely on the headspace volume. Approximately 0.5% of the total can volume must be left for headspace. Foods easily react with oxygen; color, flavor, and wholesomeness may change because of reactions with the air components.

Air evacuation from the headspace, as well as from the bulk of food, is necessary to achieve good heat penetration and the desired sterilization temperature. When large meat pieces are canned, exhausting during filing and closing is enough for a complete air evacuation. Conversly in meat batter air is incorporated during almost all processing opetarions if these are not carried out in vacuum.

Air evacuation from the headspace reduces the risk of causing a rise of internal pressure during heat treatment, resulting in can blowing or deformation. Air exhaustion also rduces the risk of promoting growth of aerobes, particularly if the product is only pasteurized.

Exhausting can be achieved by heating, by mechanical operations, and by vapor injection. Heating of water promotes an increase in its vapor pressure, and the air in the container is replaced by the water vapor, the cans are then immediately closed. When the cans are cooled down, vacuum is produced due to condensation of the water vapor. Heating at 75˚ C to 95˚ C is applied just before filling and closing.Alternatively, cans be conveyed on a belt into a exhausting chamber or tunnel in which the cansa re heated at 85˚ C to 95˚ C, removing 90% or more of the air in the head space.

4.3. Sterilization

Thermal treatments include two cycles:

1. heating

2. cooling

Whereas heating is involved in microbial and enzyme inactivation, cooling is applied for several reasons, such as easy handling and reduction of sensory characteristic deteriorations.

5. Alterations In canned Meat

Canned meat can undergo different type of alterations; most of them affect the quality of food. Besides alterations before heat treatment, in-line alterations could be caused by microbial activity, chemical reactions of the meat with the container, and physical alterations

5.1. Alteration Before Heat Treatment

These alterations occur when there is a delay in can filling and closing, or prior to heat processing, causing microbial growth to take place. It is recommended that processing must not be delayed more than 20 minutes after closing the cans.Further heat treatment may sterilized the product but gas or other microbial metabolities remain in the can.

5.2. Microbial Alterations

Alterations due to microorganisms are the result of insufficient thermal treatment.

As a consequence, certain microorganisms survivce, some of them producin gas, resulting in blown cans. Other surviving microorganisms, such as lactic acid bacteria, generate acid without gas.

When this alteration occurs, the first step to be taken is identfy the responsible microorganism; in most cases they are sporulated bacteria. Process conditions and microbial quality of raw materials must be checked, as well as sanitation of the equipment, water supply, and so forth. Insufficient thermal treatment can also be a result of can disribution in the retort, causing a delay in convection.

When cooling after heating is insufficient, themophiles can grow. As a general rule canned meat products cooled at 35˚ C. At this temperature the can outer surface rapidly colls down. However, if cans are stored in large blocks, further cooling is slow, allowing thermophiles to grow. Microbial contaminations also occurs through seals if cooling water lacks adequate sanitary quality. Recontamination after heat treatment is one of the most common problems, and cause of can blowing.

5.3. Chemical Alterations

Blowing can also occur as a consequence of reactions of meat components with the packaging material, producing hydrogen or stannus sulfide. This happens during corrosion if the can coating present failures or if the tin layer is not thick enough.

This reaction produces blue-black spots in the food. Tin cans reacts without producing any visible alterations, although flavor can be drastically altered, producing an astringent, metalic taste.

Meat compounds can also undergo chemical changes promoted by heat treatment, such as maillard reactions. This seldom occurs in meats.

5.4. Physical Alterations

Physical alterations occur as the result of mishandling of the sterilization equipment, such as a fast pressure increase in retorts, insufficient vacuum, or excessive can fill. These alterations include deformation of the cans during inadequate use of the retort.

If pressure reduction is carried out at a higher rate, higher pressure builds up inside, can producing tension and distortions that appear as blowing.

When a can blows in the bottom end and end can be slightly pressed back to its original shape, the cause is insufficient exhaustion. Presence of air in the can promotes an excessive internal pressure during heating as aresult of gas expansion. Excessive filling can also cause can deformation during heat processing due to expansion of the food. This mainly occurs in products cooked inside the can, such as luncheon meat.

6. Conclusion

Meat is a highly perishable material so many preservation techniques are developped. The main objective of heat treatment are enzyme inactivation, and destruction of pathogens and spoilage microorganisms. Meat canning is the most effective technique to preserve characteristic of meat due to developping technology, other methods generally traditional methods and they cause alterations on texture and sensory characteristics of meat.

7. References

1. Meat Science and Applications, Y.H. Hui, Wai-Kit Nip , Robert Rogers

2. The Science of Meat and Meat Products, James F. Price, Bernard S. Schweigert

Aseptic Processing vs. Conventional Canning

Aseptic Processing vs. Conventional Canning


1. Canning overcooks foods, giving poor quality
2. Cans are inconvenient and unsafe

Aseptic Processing
Aseptic Bag vs. Can
“Aseptic Processing and Packaging means the filling of a commercially sterilized cool product into presterilized containers, followed by aseptic hermetical sealing, with a presterilized closure, in an atmosphere free of microorganisms.”

“Commercial Sterility of equipment… means…free of viable microorganisms having public health significance, as well as microorganisms of nonhealth significance, capable of reproducing in the food under normal nonrefrigerated conditions of storage and distribution.”

“Low-acid foods means any foods, other than alcoholic beverages, with….
pH greater than 4.6 and a Water activity (aw) greater than 0.85….
Tomato products having…pH less than 4.7 are not classed as low-acid…”
Heat Exchangers
Brick Packs
Batch Retort
The problems with cans and jars (aseptic alternative):
1. Overcooking because of slow heat transfer to and from the center of the container (HTST processing).
2. Overcooking means poor food quality (HTST reduces overcooking).
3. Containers are limited in size to #10 or smaller (single serving to tanker ships).
The problems with cans and jars:
4. Cans are difficult to open. (plastic and paper more easily opened)
5. Opened can lids are sharp and cause cuts, insurance claims. (plastic and paper safer)
6. Partially used cans difficult to reseal, bulky to store. (zip locks reseal, bags collapse)
7. Cans make bulky rubbish (plastic and paper collapse more easily)
The problems with cans and jars:
8. Blanch for shrinkage, before canning. (blanching and cooking are one step)
9. Cans/jars must be filled with liquid for heat transfer. (liquid can be drained before packaging)
10. Energy and water intensive. (reduced energy and water consumption)
The problems with aseptic processing:
1. Technology intensive, mechanically complex system.
2. Not yet practical for low-acid foods with particles.
3. Paper and plastic more permeable than metals cans and jars—oxygen is a problem.
4. Capital already invested in canning.
Container/Surface Sterilants
Hydrogen Peroxide (H202) –FDA approved in 1981, considered a breakthrough.
Heat (steam or hot air)—not compatible with plastics, good for metal drums.
Iodine—NFCOJ silos.
Irradiation —popular for bag-in-box.
Other—UV, Acetic Acid, Ozone, etc.
Sterilizing Bulk Storage Tanks
1.Potable water rinse
2.Wash w/ caustic solution
3.Phosphoric acid rinse
4.Fill w/ iodine solution
5.Drain with filter-sterilized Nitrogen
6.Sterilize piping with hot water
Juice tanks
Stainless steel
100,000 gal
NFCO Orange juice
Bulk Storage Tanks
Store NFCOJ one year @ 35 F.
Keep sterile for 4 years.
Stainless steel for smaller tanks.
Epoxy lined carbon steel for larger tanks.
Typical size: 1,000,000 gallons.
Over 100 such tanks in use.
Tanker ship: 3.2 million gallons.
Hold Tube
1.Measure temperature at both ends.
2.No heating allowed.
3.Not insulated (Hold tubes may be insulated to
protect the hold tube from external extreme temperatures.
This is acceptable as long as no external heat source is
applied to the hold tube ).
4. Away from drafts and drips.
5. Slope upwards 0.25 inch per foot to avoid
air pockets and ensure self draining.
Hold Tube
6.Only hold tube time counts toward lethality (not heat exchanger times).
7.Fastest increment (shortest residence time) must be sterilized.
8.Solid particle residence time and temperature unpredictable, so no FDA approved system is in commercial use to aseptically process low-acid foods with particles.
Process Development
PDA Mushroom Processing Project
(Walker and Beelman)
1.Configure our system for mushrooms.
2.Determine operating conditions for optimal mushroom quality.
3.Compare yield and quality of segmented-flow processing with canned mushrooms.
4.Demonstrate technology to Pennsylvania food processing industry.
5.Final Report
Aseptic vs. Canning
Whole Mushrooms (Nate Anderson)
6.1% Higher yield
3.1% Greater whiteness (L-value ratio)
6.0% Less color change (ΔE ratio)
3.9% Better texture (Shear work ratio)
Apple Slices (Manolya Oner)
14.6% Higher yield
1.82% Greater whiteness (L-value ratio)
2.01% Less color change (ΔE ratio)
45.1% Better texture (Shear work ratio)
Aseptic Processing…….
…hope it’s been “enlightning”!