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heads that are bonded to the sleeve with rf induction (15).

To ensure a good bond, a foil laminate disk, called a

rondelle (16), is placed over the shoulder of the tube.

The sleeve is butted against the rondelle, and the rf

bond is made. This approach still requires a urea or PBT

insert to act as a ﬂavor barrier.

NEW TUBE CONCEPTS

The relatively recent appearance of ethylene–vinyl alcohol

(EVOH) (see Ethylene–vinyl alcohol) as a clear barrier

plastic has made possible the development of an all-plastic

barrier tube (see Barrier Polymers). Coextrusion methods

are available for producing laminates, and the Japanese

have produced coextruded sleeves and blow-moled barrier

tubes (7). The latter tubes have a continuous barrier; that

is, there are no higher permeation areas such as side

seams or head bonds. At present, the all-plastic barrier

tube is not economically competitive with a laminated

structure. EVOH costs about the same as aluminum foil,

so there are no material cost savings involved. The

advantage of being able to print ﬂat web is an important

factor in the cost of the laminated tube which would

appear to limit the appeal of this new concept. However,

a signiﬁcant drop in the price of EVOH relative to

aluminum foil or the development of a new market where

higher-barrier properties are required could quickly

change its importance. As well as the newest tube, poly-

foil, made by Plastube of Canada.

BIBLIOGRAPHY

1. A. Strahm, U.S. Patent 2,673,374, March 30, 1954 (to Amer-

ican Can Co.). (Describes basic heading concept.)

2. R. Brandt and J. Piltzecker, U.S. Patent 3,849,286, November

19, 1974 (to American Can Co.). (Details the sleeve extrusion

process.)

3. M. Downs, U.S. Patent 3,047,910, August 7, 1962 (to Plasto-

mer Development Corp.). (Offers good description of basic

Downs heading machine.)

4. R. Tartaglia, U.S. Patent 3,591,896, July 13, 1911 (to Peerless

Tube Co.). (Contains good drawings of the basic commercial

machine using the Downs process.)

5. K. Magerle, U.S. Patent 4,352,775, October 5, 1982 (Shows

Magerle heading process.)

6. V. Flax, U.S. Patent 3,824,145, July 16, 1984 (to Continental-

plastic AG). (Contains good drawings of spin-welding method

of heading.)

7. M. Yamada, T. Sugimoto, and J. Yazaki, U.S. Patent 4,261,482,

April 14, 1981 (to Toyo Seikan Kaisha, Ltd. and Lion

Hanigaki Kabushiki Kaisha). (Describes blow-molded tube

with EVOH barrier.)

8. R. Brandt and R. Kaercher, U.S. Patent 3,260,410, July 12,

1966 (to American Can Co.). (Shows basic laminate structure.)

9. R. Brandt and N. Mestanas, U.S. Patent 3,347,411, October

17, 1967 (to American Can Co.). (Basic article patent of

laminated tube.)

10. D. Haas, U.S. Patent 3,505,143, April 7, 1970 (to American

Can Co.). (Shows laminating process.)

11. A Grimsley and C. Scheindel, U.S. Patent 3,388,017, June 11,

1968 (to American Can Co.). (Describes side seaming of

laminated sleeves.)

12. W. Gillespie and H. Inglis, U.S. Patent 4,210,477, July 1, 1980

(to American Can Co.). (Illustrates rf induction seaming coil

design.)

13. A. Grimsley, U.S. Patent 3,565,293, February 23, 1971 (to

American Can Co.). (Describes head inserts.)

14. U.S. Patent 4,200,482, April 29, 1980 (to KMK AG). (Shows

Magerle side seamer.)

15. G. Schmid and R. Jeker, U.S. Patent 4,123,312, October 31,

1978 (to Automation Industrielle SA). (Shows AISA seaming

and heading process.)

16. A. Kohler, U.S. Patent 4,448,829, May 15, 1984 (to Automa-

tion Industrielle SA). (Shows AISA rondelle.)

General References

N. L. Ward, ‘‘Cold (Impact) Extrusion of Aluminum Alloy Part,’’ in

T. Lyman, ed., Metals Handbook, Vol. 4, 8th edition, American

Society for Metals, Metals Park, OH, 1969, pp. 490–494.

(Discusses impact extrusion of aluminum in general, with

little speciﬁc information on tubes.)

ASTM Committee on Aluminum and Aluminum Alloys, ‘‘Intro-

duction to Aluminum’’ in Metals Handbook, Vol. 2, 9th edition,

American Society for Metals, Metals Park, OH, 1979, pp. 3–23.

(Brieﬂy refers to aluminum alloys.)

Packaging in Plastic and Glaminate Tubes, Washington Technical

Center, American Can Co., Washington, NJ. (A nontechn-

ical presentation of the manufacture of tubes and a good

write-up on the problems of packaging in tubes and what to

look for.)

Patents Describing the Strahm Process Of Heading, All

Ultimately Assigned to American Can Co.

A. Strahm, U.S. Patent 2,713,369, July 19, 1955 (Illustrates

sections of tube head and sleeve.)

A. Quinche and E. Lecluyse, U.S. Patent 2,812,548, November 12,

1957 (Shows the concept of split-thread plates.)

A. Quinche, U.S. Patent 2,994,107, August 1, 1961 (Describes ﬁrst

stationary-die heading machine.)

1258 TUBES, COLLAPSIBLE

VACUUM PACKAGING

RICHARD PERDUE

Taylor, South Carolina

From World War II came plastics, the wide commercial

application of mechanical refrigeration, self-service super-

markets, the superhighway system, and a growth econ-

omy. During the late 1940s, Dewey and Almy Chemical

Company purchased the patent and brought a new and

unique French packaging development to the United

States. The ﬁrst signiﬁcant commercial application of

this concept was for vacuum packaging of whole turkeys

using rubber stretch bags. These were soon replaced with

PVDC shrink bags. The concept led to the wide commer-

cial use of vacuum packaging for perishable (refrigerated

and frozen) food: the Cryovac (registered trademark)

vacuum-packaging process. In the Z45 years since,

many individuals and companies have contributed to the

technical advancement and wide successful commercial

use of vacuum packaging for the preservation, distribu-

tion, and marketing of perishable foods. In future annals

of history, vacuum packaging of perishable foods in ﬂex-

ible and semirigid plastic ﬁlms should be ranked right up

there with canning, pasteurizing, and quick-frozen foods

as a technological breakthrough that contributed greatly

to improving the quality of life for humankind!

Vacuum packaging involves the placing, either manu-

ally or automatically, of a perishable food inside a plastic

ﬁlm package and then, by physical or mechanical means,

removing air from inside the package so that the packa-

ging material remains in close contact with the product

surfaces after sealing.

Packaging in this manner, depending on the product

being packaged the barrier properties of the packaging

material, the level of air removal, and storage tempera-

ture, can substantially retard chemical and/or microbial

deterioration of the food product. In many instances, this

dramatically extends eating quality life.

AIR-REMOVAL SYSTEMS AND PACKAGING EQUIPMENT

Nozzle Vacuuming. Using this method of air removal,

a nozzle connected to a vacuum pump is inserted inside

the open end of a preformed bag or pouch (see Figure 1).

The vacuum or air removal level using the nozzle system

is seldom high, as the packaging material (depending on

its modulus) quickly collapses onto the product surface

and blocks signiﬁcant air removal. Today, nozzle vacuu-

mizing is widely used for packaging whole fresh and

frozen poultry, fresh-cut vegetables and bulk packaging

of fresh meats, poultry, ﬁsh, processed meats, nuts, and

so on.

For whole poultry, manual and high-speed rotary noz-

zle machines that provide an aluminum clip closure are

used. The twisting of the bag neck and clipping provides

for good whole-bird shaping and sealing under high-

moisture conditions. Nozzle vacuumizing provides for

good bag to product (bird) cling, without collapsing the

body cavity as can happen with high-vacuum-chamber

systems.

For cut vegetables and bulk packaging, manual and

semiautomatic nozzle vacuumizing combined with heat

sealing predominates.

Chamber Vacuumizing. Using this method, the product

is placed inside the ﬂexible plastic ﬁlm package, which is

loaded into the bottom section of a vacuum chamber

(Figure 2). Such systems usually consist of a top chamber

and a bottom chamber. The chamber is closed, and a high

vacuum is [in both cubic feet per minute (cfm, i.e., mL/

min) and inches of mercury (in. Hg)] drawn on the

chamber both inside and outside the package. Some

chambers are usually vacuumized to Z29 in. Hg.

Figure 1. Nozzle vacuuming.

1259

Chamber vacuumizing machines generally employ

heat-seal closures and are available from manual through

fully automatic rotary high-speed units. Such equipment

uses shrink bags and laminate pouches. They are widely

used to package fresh primal and subprimal meat cuts,

smoked and processed meats, and natural cheeses. Some

chamber units are also available that provide an alumi-

num clip closure inside the chamber.

Two other widely used chamber vacuumizing systems

use rollstock ﬁlms rather than preformed bags and

pouches: thermoforming and vacuum skin packaging

(VSP).

Thermoforming. Thermoforming vacuum-packaging

machines dominate the packaging of consumer units of

wieners, sliced luncheon meats, sliced bacon, smoked

sausages, and some natural cheeses (Figure 3). Such

machines operate using two rolls of multilayer (usually

high-O

-barrier) plastic ﬁlm (top and bottom webs). The

operation of a thermoforming machine involves feeding

the bottom web into the machine by clamping the web by

its edges and indexing it either (a) over a continuously

moving train of thermoforming dies (pockets) or (b) in a

parallel set of clamping chains that ﬁrst indexes

the bottom web over a thermoforming station. In both

web-handling modes, the bottom web is heated, then

vacuum and/or pressure formed.

The product is manually or automatically loaded into

the formed pockets. The top web is then fed down over the

bottom web between the two halves of the vacuum-sealing

chamber. The two halves of the chamber close and a high

vacuum ( Z29 in. Hg) is drawn on both sides of both webs

and around the product. When the desired vacuum level is

reached, the webs are heat-sealed together. The cham-

ber(s) is (are) vented to atmosphere, opened, and the

packages indexed out the machine and slit into individual

units (see the Thermoforming article).

Vacuum Skin Packaging. There are great similarities

between VSP (Figure 4) and thermoforming machines,

with the primary differences involving how the forming

web (bottom web in thermoforming and top web in VSP)

is thermoformed and the plastic ﬁlm structures used.

Like thermoforming in an automatic VSP machine, the

bottom web is fed through the machine by a parallel set

of clamping chains. The bottom web may or may not be

thermoformed slightly. It can be an oxygen barrier,

nonbarrier ﬂexible, or semirigid web. Again, as with

thermoforming, the product is loaded onto the bottom

web, a top web is fed down over the bottom web, and

both are indexed between the two halves of a vacuum

(skin) packaging chamber (see the Skin packaging

article).

As the top web is fed down and into the VSP chamber, it

is heated and may be partially thermoformed to ﬁt over

the product. When the chamber closes, the bottom web is

pulled against the bottom of the VSP chamber with a high

vacuum. The top web is either (a) suspended over the

product by drawing an equal vacuum over both sides of

the web and around the product or (b) is drawn against the

heated surfaces of the upper half of the VSP chamber by a

high vacuum, and the area around the product between

the top and bottom webs is vacuumized. When the desired

vacuum level is reached, the vacuum to the top of the

chamber is vented to the atmosphere, and the heated top

web instantaneously thermoforms to the shape of the

product. At the same time, the two webs heatseal to

each other wherever they come in contact. The bottom

Figure 2. Chamber vacuumizing.

Figure 3. Thermoforming. Figure 4. Vacuum skin packaging.

1260 VACUUM PACKAGING

chamber half is then vented, and the packages index out;

they are slit into individual units as they do so.

Pressure. Probably the most simple means of producing

a vacuum or negative-pressure package is through apply-

ing pressure to the outside of a bag or pouch that contains

a product. Two methods have been used commercially. In

the early days of fresh-red-meat vacuum packaging, a

system of air removal involved holding a bag (with pro-

duct) by its open end and lowering it into a tank of water

so that the product was completely submerged with the

open end of the bag still above the water, which forced air

out. The open end of the bag was then gathered and closed

with an aluminum clip.

Another pressure method used with bags and laminate

pouches and today in packaging fresh cut vegetables is to

squeeze the air out with sponges and heat seal the

package prior to releasing the squeezing action of the

sponges.

Hot Fill. This process is used to package pumpable

prepared foods in ﬂexible, oxygen-barrier plastic ﬁlm

packages. By hot ﬁlling, usually above 1801F, steam is

present, which helps to exhaust air from the product and

headspace of the package just prior to sealing. Such

packages are then rapidly chilled, which creates a package

with a negative pressure inside (Figure 5).

Following is a discussion of each perishable-food cate-

gory with emphasis on why speciﬁc vacuum-packaging

systems are used to preserve, distribute, and market each.

Poultry. Vacuum packaging of fresh poultry is done

primarily to retard the growth of aerobic spoilage bacteria,

and to provide an attractive leakproof (moisture) package

(Figure 6). When packaging fresh poultry, care must be

taken to avoid establishing conditions that support

the growth of H

S-producing bacteria. These bacteria

are commonly present on fresh poultry and grow best

above 341F and under low-O

conditions. Therefore, fresh

whole Rock Cornish, roasters, and turkeys are vacuum

packaged using O

-permeable shrink bags. Some cut-up

fresh poultry is now being vacuum-packaged using

thermoforming and O

-permeable structures. Some bone-

less/skinless parts are being vacuum-skin packaged.

As for frozen whole and portioned fresh poultry, va-

cuum packaging in O

permeable shrink bags dominates.

The bags are coextruded, multilayer polyoleﬁn structures

with a modiﬁed polypropylene (PP) outer layer to provide

high gloss and freezer-case scuff resistance, and an

electron-beam crosslinked polyethelene (PE) inner layer.

This PE layer provides cold-abuse toughness, high hot-

water shrinkability, and both heat and clip sealability.

Good wrinkle-free ﬁlm-to-product cling provided by the

vacuumized shrink bag is essential for attractive, frost-

free packages. A high oxygen barrier is not required as

frozen fresh poultry does not develop signiﬁcant oxidative

rancidity during typical storage and distribution.

Fresh Red Meats (Beef, Pork, Veal, Lamb, and Venison).

Today about 90% of the fresh beef primal and subprimal

cuts shipped to food service and retail are vacuum-pack-

aged in high-oxygen-barrier shrink bags (Figure 7). Such

bags are made of coextruded materials consisting of an

outer EVA or linear low-density polyethylene (LLDPE)

layer, a PVDC barrier layer, and an electron-beam

crosslinked EVA or LLDPE heat-sealable/clipable inner

layer.

Figure 5. Hot ﬁll.

Figure 6. Vacuum packaging for poultry.

Figure 7. Vacuum packaging for red meat.

VACUUM PACKAGING 1261

Most fresh-red-meat (FRM) vacuum packages are pro-

duced on high-speed, high-vacuum, heat-sealing rotary

chamber packaging machines. For bone-in FRM cuts, bags

are available with bone-puncture-resistant patches lami-

nated to the outside. Veal and lamb cuts are also vacuum

packaged in this manner. The application of this technol-

ogy was slow to develop for fresh pork. Several years ago

the industry did start using this technology for boneless

loins and tenders. With the advent of the ‘‘boneguard’’

shrink bag, bone-in loins were successfully packaged. The

industry is now rapidly converting to shrink-bag vacuum

packaging of bone-in pork loins for retail distribution.

The ‘‘aging’’ of beef is a tenderizing process that takes

place as a result of naturally present enzymes. Vacuum

packaging was ﬁrst applied to beef by purveyors to age

steaks and roasts for the food-service industry. Beef could

be ‘‘aged’’ for up to 30 days without any signiﬁcant shrink

or trim loss. It was then applied to beef (later to veal, lamb,

and pork) for retail, which dramatically improved the

distribution and marketing. In fact, this development

ultimately resulted in a total restructuring of the beef

industry. The preservation aspects of FRM barrier shrink

packaging are threefold: (a) retard the growth of aerobic

spoilage microorganisms, (b) prevent the chemical degra-

dation of myoglobin, and (c) minimize the loss of moisture.

As FRM is chemically alive and using some oxygen,

oxygen permeability below 200 mL/m

will shift the micro-

bial population from aerobes to facultative anaerobes

(lactic acid producing). To minimize myoglobin degrada-

tion and provide adequate red-color (oxymyoglobin) re-

generation and stability for retail display, oxygen

permeabilities below 50 mL/m

are required. Most of the

barrier shrink bags used today have O

permeabilities

below 30 mL/m

. As shrink bags are excellent moisture

barriers, the moisture loss of major concern is ‘‘purge’’

(free liquid that separates from the meat). The cut of FRM

packaged, temperature, and other product factors inﬂu-

ence moisture separation.

From the package standpoint, the absence of minute

negative pressure voids or cavities is critical. The applica-

tion of high package vacuum to maximize ﬁlm to product

surface cling, and excellent hot-water shrink to minimize

ﬁlm wrinkles, provides for the least purge development.

Fresh ground beef and pork sausage are major FRM

product categories. Although not truly vacuum packaged,

they are pressure packaged in tubular oxygen-barrier

packages. Today, most packages for these products are

produced on vertical form/ﬁll/seal machines that provide

metal clip closures. The ﬁlms used are coextruded struc-

tures. For ground beef: PE or EVA/nylon/EVOH, nylon/PE,

or EVA with appropriate tie layers. For pork sausage: EVA/

PVDC/EVA.

For individually cut fresh and frozen steaks distributed

primarily to food service, thermoforming vacuum packa-

ging and vacuum skin packaging are widely used.

For fresh steaks, oxygen-barrier structures are required:

Thermoforming: nonforming web-biaxially oriented

nylon or PET/PVDC/LLDPE or Surlyn (DuPont)

Forming web: cast nylon/EVOH/LLDPE or Surlyn

Vacuum skin packaging: forming web—PVDC/Surlyn

or coextruded, electron-beam crosslinked LLDPE/

EVOH/LLDPE

Nonforming web, similar to the nonforming web used

in thermoforming

For frozen steaks, structures are similar to those used

for fresh except the PVDC or EVOH layers are left out.

Cured, Smoked, and Processed Meats. This category

includes such products a wieners, bacon, hams, loaves,

smoked sausages, sliced luncheon meats, and corned beef.

Today such products are manufactured using both red

meats and poultry. These products are vacuum packaged

in high-oxygen-barrier materials to retard aerobic micro-

bial growth, prevent cured color degradation, and loss or

degradation of the cooked and smoked ﬂavors and devel-

opment of fat rancidity (Figure 8). As chemical changes

are of greatest preservation concern, products in this

category are chamber vacuumized to minimize residual

within the packages. Wieners, sliced bacon, and sliced

luncheon meats are packaged using materials with O

permeabilities below 15 mL/(m

24 h). To prevent curing-

induced color degradation, they are generally packaged

using high-speed laminate rollstock thermoforing ma-

chines. The forming web is a coextruded or extrusion

structure consisting of nylon/PVOC or EVOH/Surlyn or

LLDPE with appropriate tie layers if coextruded. The top

layer will be polyester or oriented-nylon PVDC coated and

reverse-printed if desired; also it could be adhesive or

extrusion laminated to Surlyn or LLDPE sealant.

The larger units such as loaves, hams, and corned beef

are usually packaged using high-barrier shrink bags—

coextruded EVA, LLDE/PVDC/EVA, LLDPE (electron-

beam crosslinked). The packages are vacuumized and

heat sealed using high-speed rotary chamber machines.

Natural Cheeses. Vacuum packaging of cheeses for cur-

ing and for loaves and consumer units of cured cheeses

(Figure 9).

Figure 8. Vacuum packaging for cured, smoked, and processed

meat.

1262 VACUUM PACKAGING

Curing. Cheddar cheese is formed into 40-lb rectangu-

lar blocks and vacuum packaged (chamber/heat sealed)

using oxygen-barrier shrink bags and laminate pouches

(nylon/LLDPE), then placed in strong, tight-ﬁtting corru-

gated cartons for curing 90 days and longer. The vacuum

packaging inhibits mold growth and moisture loss while

allowing the non-gas-forming microbial curing to take

place. After curing, the 40-lb blocks are cut into consumer

units or used as manufacturing cheeses. Other non-gas-

forming cheese varieties such as Gouda are also cured in

this manner. More traditional shapes such as wheels,

horns, and sticks of non-gas-producing varieties including

Italian cheeses are cured using high-O

-barrier shrink

bags (see Figure 10).

For gas-producing cheeses (during curing) such as

Swiss, high-CO

-permeability shrink bags and nylon-

based pouches are used. The O

permeability has to be

kept below 250 mL/(m

24 h) to retard mold growth dur-

ing curing.

A unique application of shrink-bag vacuum packaging

is for curing of wheels of Blue and Roquefort cheeses. After

vacuum packaging and shrinking the barrier bag tightly

around the uncured cheese wheel, which has been inocu-

lated with the desired mold, long needles are forced

through the wheel and removed to provide air channels

to allow the mold to grow and develop the blue color.

Retail Units. Chunks, sticks, blocks, loaves, and half

moons of natural cheeses are vacuum packaged using O

barrier shrink bags and laminates using material struc-

tures and equipment systems very similar to previously

described for smoked, cured, and processed meats. For

cheese, such packaging is used to prevent mold growth,

retard light-catalyzed oxidation of the butter fat on the

surface, prevent surface color fading under display lights,

and minimize moisture loss.

Fresh and Frozen Fish. With the growth of spoilage,

bacteria can be retarded by vacuum packaging fresh ﬁsh

in oxygen-barrier ﬁlms. In the United States, doing so is

looked on with disfavor by the U.S. Food and Drug

Administration (FDA). Clostridium botulin type C, which

is commonly found on ﬁsh, can grow under anaerobic

conditions at temperatures as low as 391F. This is well

within the refrigerated distribution temperature ranges

especially if abused. A vacuum-packaging system using

-permeable plastic ﬁlms has been approved for im-

proved shelf-life packaging of fresh ﬁsh.

Vacuum packaging using O

-barrier shrink bags is

being used successfully for frozen Alaskan salmon to

replace ice glazing, to eliminate moisture loss (freezer

burn) and rancidity, and for frozen tuna loin storage and

transport to tuna-canning plants (Figure 11).

Fresh Produce. A new and rapidly growing end use for

vacuum packaging is fresh-cut vegetables. Much of the

food-service industry is on a fast track to remove the

preparation of fresh vegetables from the back of the

restaurant to central plants. The processing and ex-

tended-shelf-life packaging technology is now being ap-

plied to consumer packaging of such vegetables for retail

supermarket sales. When the natural skin is removed

from a vegetable or is cut in smaller segments (sliced,

diced, etc.), extended shelf life can be provided through

properly designed protective packaging. As fresh-cut ve-

getables are still alive and respiring, concern must be

given to providing adequate O

and for release of the CO

produced. Fresh vegetables have been classiﬁed according

to their respiration needs into three general groups as

shown in the following table.

Figure 9. Vacuum packaging for natural cheeses.

Figure 10. Curing.

Figure 11. Vacuum packaging for fresh and frozen ﬁsh.

VACUUM PACKAGING 1263

Such cut vegetables are packed in permeability modiﬁed

polyoleﬁn bags or ﬁlm or vertical form/ﬁll/seal machines

(see the Form/ﬁll/seal, vertical article). Bags are typically

nozzle vacuumized and pressure squeezed to remove

residual air from the package prior to heat sealing. For

the various vegetables group, the polyoleﬁn ﬁlms are

modiﬁed through resin variations and additives to achieve

the desired O

/CO

permeability.

The polyoleﬁn ﬁlms are adequate barriers to prevent

signiﬁcant moisture loss. The removal of the air from the

package provides for the package quickly becoming a

modiﬁed atmosphere. Under adequate refrigerated condi-

tions, the O

will be maintained below 5% and the CO

the 8–12% range. This slows down respiration and will

signiﬁcantly extend the eating-quality life of the cut

vegetable. Large volumes of chopped lettuce, broccoli,

and cauliﬂower ﬂorets are now being distributed to food

service and retail in this manner. The vacuum or negative-

pressure package also provides a good visual-quality

measure of the package and product for both the producer

and end user (Figures 12–14).

BIBLIOGRAPHY

General References

‘‘Advances in Fish Science and Technology,’’ in Proceedings, Torry

Research Station Conference, Aberdeen, Scotland, 1979.

Chilled/Refrigerated Foods Conference, Proceedings, The Packa-

ging Group, Inc., 1988.

A. L. Brody, Controlled/Modiﬁed Atmosphere Packaging of Foods,

Food and Nutrition Press, Turnbull, CT, 1989.

E. Karmas, Meat, Poultry and Seafood Technology—Recent Devel-

opments, Food Technology Review No. 56, Noyes Data Corpora-

tion, Parkridge, NJ, 1982.

F. Kosikowski, Cheese and Fermented Milk Foods, published by

the author, Ithaca, NY, 1966.

R. Lawrie, Developments in Meat Science—1, Applied Science

Publishers, London, 1980.

R. Lawrie, Developments in Meat Science—4, Elsevier Applied

Science, London, 1988.

F. A. Paine and Heather Y. Paine, A Handbook of Food Packaging,

Blackie Academic and Professional, London, 1992.

M. E. Rhodes, Food Protection Technology II, Lewis Publishers,

Chelsea, MI, 1990.

S. Sacharow and R. C. Grifﬁn, Jr., Principles of Food Packaging,

AVI Publishing Company, Westport, CT, 1980.

F. M. Terlizzi, R. R. Perdue, and L. L. Young, ‘‘Processing and

Distributing Cooked Meats in Flexible Films,’’ Foods Technol.

p. 38 (March 1984).

Figure 12. Vacuum packaging for fresh produce.

Figure 13. Vacuum packaging for fresh produce.

Figure 14. Vacuum packaging for fresh produce.

Film permeabilities [mL/(m

24 h)]

Respiration group Vegetables O

Light breathers Carrots, potatoes, turnips 1000–3000 10,000–20,000

Medium breathers Lettuce, celery, pepper 6000–7000 30,000–35,000

Heavy breathers Broccoli, cauliﬂower, asparagus 15,000–20,000 75,000–100,000

1264 VACUUM PACKAGING

VACUUM-BAG COFFEE PACKAGING

The concept of vacuum-bag packaging for ground coffee

was introduced in the U.S. market years ago. It had been

developed in Europe years before, but except for nonher-

metic paper bags still used in the southeastern states,

ground coffee in the United States has remained in the

three-piece sanitary can with plastic covercap that re-

placed the key-opening can about 40 years ago. The new

vacuum-bag package has been described as a ‘‘ﬂexible can,’’

because it delivers the same vacuum-packed fresh coffee

that the consumer buys in the can, but that is where the

similarity stops. The ‘‘vac-bag’’ is rectangular rather than

round, and it can be shelved standing up, or lying on its

side like a ‘‘brick,’’ which is one of its less-glamorous names.

Coffee Characteristics. Coffee has some unique charac-

teristics. After coffee beans are roasted, they slowly evolve

amounting to over 1000 cm

/lb (2200 cm

/kg) of pro-

duct depending on the blend and roasting color. During

grinding, the volume of CO

is reduced to about half, and

depending on the grind size, it requires varying holdup

times before packing. Grind size varies greatly depending

on the type of coffee-brewing equipment used and indivi-

dual taste preference. Typical ﬁne grind for most Eur-

opean countries is 500–600 mm; North American coarser

grinds are 800–1000 mm. Vacuum-bag packaging of coarser

grinds present more of a problem because of slower

degassing. At 6–8 in. Hg (20–27 kPa), a vac-bag becomes

soft and it can even balloon like a football (positive

pressure) if it has insufﬁcient degassing. Because rigid

metal cans are capable of withstanding full vacuum as

well as positive pressure, they require a relatively short

holdup time even for coarse grinds. Because ground coffee

also varies in density, the height of ﬁxed-cross-section

bags varies as well. This variation means that the equip-

ment and materials must be adaptable to a limited auto-

matic height change during a production run. In addition,

coffee must be protected from oxygen to maintain the

freshness. Vacuum packing eliminates most of the oxygen

from the package by the nature of the process.

The Vacuum Bag. The ﬁrst commercial ‘‘vac-bag’’

packages were made in the early 1960s, probably in

Sweden. At that time the package was a bag-in-box style

(see Bag-in-box, dry product) that later evolved to a lower

cost, bag-in-bag style, which is still the most widely used

type in Europe and Canada. A still lower cost style, the

single-wall bag, is being used to some extent in Europe and

by the major coffee producers in the United States. The

bag-in-bag style and the single-wall style function equally

well in protecting the product, but they differ in appear-

ance. High-quality graphics on the paper or foil/paper

outer wrap of a bag-in-bag package gives a smooth sur-

face appearance. Most single-wall bags have a rough or

‘‘orange peel’’ surface when under full vacuum. As with

any package concept with more than one style, there are

pros and cons for each, but the current U.S. market is

predominately single-wall vac bag and is likely to stay that

way.

Equipment. Because Europe spawned the vac-bag’s po-

pularity, it is no surprise that all the automatic high-speed

equipment is made there. There are three major equip-

ment suppliers who compete in the coffee-packaging area

and are as follows: SIG, Hesser, and Goglio (1–3). All have

automatic high-speed (40–120-boxes-per-minute (bpm)],

1-lb (0.45-kg)-size machines capable of forming bags from

roll stock material, ﬁlling, evacuating, sealing, and folding

the top of the bag to deliver a ﬁnished vac-bag. Bags can

be made in different ways from rollstock. Mandrel- and

tubeforming machines form the bag, which is carried

horizontally into the ﬁller. After ﬁlling it is transferred

into a vacuum chamber where it is evacuated and sealed.

It is then transferred out of the vacuum chamber to a

trimmer and ﬁnal folding of the top. Tape or hot-melt

glue are two methods used to hold the top folds in place.

The sealing of the bag is what keeps it hard and under

vacuum.

Materials. Each of the major equipment suppliers pro-

vides basic information on what packaging material prop-

erties are essential for efﬁcient vac-bag production. Some

differences exist, but many similarities also are present

for achieving a low level of defects from the machine. Each

vac-bag must be durable enough to survive the rigors

of transportation, warehousing, and retail distribution to

remain vacuum-packed at point of purchase. Although

many European packers use a three-ply structure made of

48-gauge polyester ﬁlm (OPET)/35-gauge aluminum foil

(AF)/300-gauge sealant (see Film, polyester; Foil, alumi-

num; Sealing, heat), most U.S. coffee roasters employ a

more durable four-ply structure. This structure can be

accomplished by the addition of one of several ﬁlms, such

as biaxially oriented polypropylene (BOPP) (see Film,

oriented polypropylene) or biaxially oriented nylon

(BON) (see Nylon). These structures can be constructed

in various ways but most typically as follows:

48-ga OPET/75 ga BOPP/35 ga AF/300 ga sealant

48-ga OPET/35 ga AF/60 ga BON/300 ga sealant

When these structures are designed for a single-wall

bag, the OPET is reverse-printed. Gravure printing (see

Printing) on OPET provides excellent graphics, high gloss,

and a scuff-resistant package. Vacuum-metallized ﬁlms

(see Metallizing vacuum) have been used successfully in

Europe and Canada as lower-cost foil replacements. Be-

cause their oxygen barrier may be lower than foil, each

coffee packer must determine if nonfoil structures provide

adequate barrier.

Currently, the best method to joint these materials

into a ﬁnished structure is by adhesive lamination

(see Laminating; Multilayer ﬂexible packaging). To pro-

duce a ﬁnished structure with uniform-gauge control,

high internal bond strength, minimum curl, and a

controlled coefﬁcient of friction, adhesive lamination

has proven to be an excellent converting system. Both

VACUUM-BAG COFFEE PACKAGING 1265

solvent- and solventless-type adhesive laminators (see

Adhesives; Coating equipment) are now converting mate-

rials in the United States and Canada for coffee packers.

These new high-speed automatic packaging machines

require consistently high-quality materials to operate

efﬁciently. All of the material converters acknowledge

the sometimes difﬁcult learning experience on vac-bag

ﬁlms and the need to set up a very thorough quality-

control system.

Valves and Sorbents. Gas-off of CO

from ground coffee

is a problem for vac-bag packagers that can be handled in

several ways. The simplest solution is to grind the coffee

beans very ﬁne, as in Europe. The ﬁne grind evolves gas

more quickly and requires only a short holdup time (1

–

2 h). The North American markets require coarse grinds,

however, that need up to 24 h of holdup time and con-

siderable storage capacity. Two methods exist to eliminate

all holdup time. One is the one-way coffee valve, which

allows CO

out of the bag without allowing O

into the bag

(see Valves). The bag, however, is soft. This concept was

tested in the United States by two major roasters, but it

was abandoned in favor of the hard vac bag that consu-

mers seem to prefer. The other method involves a new

technology from Canada, whereby a CO

-sorbent pouch is

placed in the coffee bag much like a desiccant pouch is

used for moisture-absorbing applications. This new coffee

vac-bag technology allows the roaster to package freshly

ground coffee without any holdup time and still obtain a

hard vacuum bag. This beneﬁt is not possible with any

other system.

A growing coffee market has been found in specialty

and gourmet stores where whole beans are purchased.

The beans are generally not hermetically packaged, so

gas-off is not an issue. In this case, the use of a one-

way valve is an excellent way to achieve an air-

tight package and keep the beans fresh. The valve can

be heat-sealed into the bag ﬁlm as done by Goglio and

SIG. It also can be attached to the outside surface

using a pressure-sensitive valve concept developed by

Hesser.

Advantages. Vac-bag is seen as a low-cost package

compared with metal cans. For some coffee packers, this

low-cost advantage may be true if bag packing line speeds

are equal to or greater than those for cans. For others,

where the reverse is true, the material-cost advantage is

not as large. Current 1-lb-size (0.45-kg-size) metal cans

that include plastic overcap cost about $0.17–$0.19. A

high-quality four-ply vac bag costs about $0.08–$0.10,

which provides a material-cost advantage of about 9 cents

per 1-lb (0.45-kg) package. Additionally, advantages are

present in storage, handling, and shelving a vac-bag

because of its compact shape. The reduction in cube is

dramatic (35%). This cube reduction is beneﬁcial to both

manufacturer and retailer, because warehousing and

shelving space is always a premium. As vac-bags become

more widely distributed, consumers will determine the

future for this new package.

BIBLIOGRAPHY

‘‘Vacuum-Bag Coffee Packaging’’ in F. J. Nogent, ed., The Wiley

Encyclopedia of Packaging Technology, 1st ed., by General

Foods Corp., pp. 690–691.

1. Product literature, SIG Swiss Industrial Company, Repre-

sented by Raymond Automation Company, Inc., Norwalk, CT.

2. Product literature, Hesser Division of Bosch Package Machin-

ery, S. Plainﬁeld, NJ.

3. Product literature, Goglio, represented by Fres-co System

USA, Inc., Telford, PA.

VIBRATION

JORGE MARCONDES

San Jose State University,

San Jose, California

Vibration describes oscillation in mechanical systems.

Packages, products, pallet loads, vehicles, machinery,

and equipment are mechanical systems. They are sub-

jected to vibration whenever there is movement. In packa-

ging applications, vibration can be either desirable or

undesirable, although often it is undesirable, because it

can damage products. Examples of packaging applications

of desirable vibrations are a ﬁlling machine and an ultra-

sonic heat sealer. Filling machines may have a vibratory

tray feeder to dispense the product into a package; an

ultrasonic heat sealing uses high-frequency mechanical

vibrations to produce localized heat that melts the inter-

face between the sealing materials only, without affecting

the product or the rest of the package. However, vibrations

encountered in vehicles during distribution are always

undesirable. This article concentrates on vibrations in

distribution only, or those that are undesirable.

Vibration always occurs in distribution because the

operations of transport and handling always move goods.

It can inﬂuence products to the point of causing physical

damage or product spoilage. Studies have shown that

vibration in vehicles can cause, for example, phase separa-

tion to emulsiﬁed products, bruising in fruit and vegeta-

bles, physical damage in mechanical and electronic

products, and damage to labels because of friction (1, 2).

Both external and internal sources originate vehicle

vibrations. Examples of external sources include road

pavements, rail tracks, and ocean waves; internal sources

include rotating parts such as unbalanced wheels and the

engine itself (3). In a truck, for example, the wheels of the

vehicle pick up the pavement up-and-down oscillations as

mechanical vibrations; the suspension and structure of

the vehicle transmit these, along with other internal

vibrations, to the vehicle ﬂoor. Packaged products placed

on the vehicle ﬂoor will then receive the vibrations.

Vibrations that occur in a vehicle ﬂoor may be decom-

posed in three perpendicular directions: vertical, lateral,

1266 VIBRATION

and longitudinal. Several studies investigated the direc-

tions and locations in vehicles where highest vibration

levels occur. On the basis of these studies, it is commonly

accepted today that in trucks and semitrailers the highest

vibrations occur on the rear axle and in the vertical

direction (4, 5). Product damage caused by vibration is

more likely to occur if packages are placed over the rear

axle in trucks and trailers.

The role of the packaging engineer is to design packages

that reduce vibrations. Cushions and other ﬂexible-packa-

ging systems are engineered in such a way that the

package attenuates the vibrations that occur in vehicles.

No package can completely eliminate vibration. Although

still transmitted to products, a package designed for vibra-

tion attenuation may virtually eradicate the potential for

damage.

FORCED VERSUS FREE VIBRATION

Vibrations are generally classiﬁed into two categories:

forced (when there is a continuous input source) and free

(input source discontinued). The type of vibration that

occurs in packaging machinery is a forced vibration

because a source continuously drives the system to vi-

brate. The vibration that occurs without external excita-

tion is called free vibration (6). Both types, free and forced,

occur in all vehicles during transport. As an example, the

pavement roughness is a source of vibration that forces

the wheels of a vehicle to move up and down, generating

vibration. If the source of vibration stops, then the system

will continually decrease its vibration level (free vibration

now) until a full stop, when the energy is totally dissi-

pated. Similarly, when the vehicle hits an obstacle such as

a pothole, the vibration will be forced while the obstacle is

in contact with the vehicle and free thereafter until the

effect of that particular input ends. An example of free

vibration occurs when a mass, placed on top of a spring, is

pushed down and released, and then vibrates ‘‘freely’’

after its release. Whenever a system is vibrating freely,

the movement will decrease and the vibration will even-

tually cease, because of damping. Damping is always

present in mechanical systems (7), and it dissipates the

energy that keeps the system vibrating.

FREQUENCY AND ACCELERATION

A state of vibration can be characterized by a frequency

and an amplitude. The simplest harmonic motion of a

mechanical system, such as of a mass placed on a spring

that oscillates up and down, is deﬁned by a frequency and

a peak acceleration. The frequency is the number of times

a cycle repeats itself in a unit of time, and the peak

acceleration is the maximum value of the acceleration in

the entire cycle. If a system is vibrating freely, it vibrates

at its natural frequency (8). The natural frequency is

mainly a function of the mass and the stiffness of the

system. The relationship between peak acceleration, max-

imum displacement from the position of equilibrium, and

frequency of a vibrating system is

max

ð2pf Þ

ð1Þ

where a

= peak acceleration in g (where 1 g is equal to

the gravitational acceleration), d

max

= maximum displace-

ment of the oscillating mass from the equilibrium position,

f = frequency of oscillation, and g = gravitational accelera-

tion, or 9.81 m/s

. In applying equation (1) to ideal, or

linear systems, the equation shows that the peak accel-

eration is directly proportional to the maximum displace-

ment and to the square of the frequency of vibration. In

other words, if the maximum displacement is doubled,

then the peak acceleration will also double (frequency

kept constant); if the frequency is doubled (maximum

displacement kept constant), the peak acceleration will

quadruplicate. Figure 1 shows the relationship repre-

sented by equation (1), as applied to a spring-mass system

undergoing free vibration. Equation (1) does n ot take into

account the direction of vibration (up or dow n). In Figure

1, the mass is pushed d own with the force F and then

released. The situation depicted in Figure 1 does not

sho w the effect of damping. For further information on

damping effects on free vibration, the reader may consult

Refs. (7–9).

The duration of one cycle of oscillation is shown as the

period T. The frequency of oscillation f representing the

number of cycles that occur in a unit of time is related to

the period by

f ¼

ð2Þ

For example, if the period T = 0.2 s, and d

max

= 0.5 cm

(0.005 m), the frequency is 1/0.2 s = 5 Hz (using equation

2) and a

= 0.005 m (2p5 Hz)

/9.81 m/s

= 0.5 g [using

equation (1)]. This means that the system is vibrating

with a peak acceleration of 0.5 g and the mass is oscillat-

ing at ﬁve cycles per second (5 Hz). If the peak acceleration

is 0.5 g, the acceleration at any instant will be somewhere

between + 0.5 g and 0.5 g, inclusive.

When vibration levels in vehicles reach values above

1 g (acceleration due to gravity) packages will start to

bounce. Because packages are seldom attached to the

vehicle ﬂoor, if the vertical vibration of the vehicle ﬂoor

is higher than 1 g, the package would not follow the

Figure 1. Spring-mass system in free vibration without damp-

ing: (a) force F causes displacement d

max

and releases mass to

vibrate freely; (b) displacement of mass varying with time; and (c)

acceleration of mass varying with time.

VIBRATION 1267