Single-layer elastic tubular film of polyamide used for packaging paste substances and a process for the production of such film

The present invention relates to a tubular film used for packing foodstuffs in paste form, this tubular film being polyamide that can absorb at least 5% water, and which at an internal pressure between 0 and 0.6 bar permits substantially reversible deformation and which has a matt appearance. The present invention also relates to a process for the production of this tubular film by multiaxial stretching of the primary tube with stretch ratios of at least 1:2.3 in the longitudinal direction and at least 1:2.5 in the transverse direction, and total thermal fixing of the stretched tube during controlled shrinkage. In addition, the invention describes a boiled or cooked sausage as well as a soft cheese, these being packed in a tubular film according to the invention.

This invention relates to a single-layer elastic tubular film of polyamide, 
used for packaging paste materials, particularly foodstuffs, that are 
packed when hot, or else are subjected to heat treatment after packing, 
and to a process for producing this film. 
In particular, the present invention relates to a tubular film that can be 
used as a sausage casing for table sausages and boiled sausages, and can 
also be used for goods such as soft cheeses that are packaged in a 
semi-liquid state. 
Various demands are imposed on tubular films of this kind, particularly if 
they are used as sausage casings for boiled and table sausages, and in 
part these demands are mutually exclusive. If one relinquishes the 
requirement of smoke permeability, it is possible to use tubular films of 
thermoplastic materials that meet most requirements such as low price, 
problem-free processing, low permeability with regard to gases, water 
vapour, and undesirable bacteria. However, up to now nearly all of the 
thermoplastic materials used as sausage casings have the disadvantage that 
once the sausage has been boiled and subsequently cooled they do not fit 
round the sausage material closely, in the manner of a natural casing, but 
appear to be more or less wrinkled. The customer equates such wrinkled 
appearance with old goods that are no longer fresh, and this is an 
obstacle to sale. For this reason up to now such sausage casings of 
thermoplastic materials have only been used by sausage makers for 
second-rate goods. Various proposals for solving this problem have already 
been made. Thus, German Pat. No. 21 32 259 describes a device used to 
produce a stretched tube of thermoplastic material that can be shrunk. In 
this connection, a tube preferably of polyamide 12 is drawn--and thereby 
stretched--over a stretching bar whilst being heated and then subjected to 
controlled air cooling, the anticipated transverse contraction being 
hindered by the bar. Sausages packaged in these casings also appear 
wrinkled after overnight cooling and, in order to achieve a smooth 
appearance they must be immersed once again for a few seconds in boiling 
water. This causes the casing to shrink and lie almost wrinkle-free 
against the sausage material. However, this additional stage is not 
desirable in a processing sequence and this has meant that for all 
practical purposes these casings cannot be used. 
Further attempts to solve this problem relate to two-layer sausage casings 
and exploit the phenomenon of dry shrinkage that occurs if moist 
hydrophilic films are dried and thereby contract in all dimensions. Thus 
German Pat. No. 13 02 384 describes a process for the production of a 
multi-layer sausage casing that consists of a cellulose fibre layer that, 
on the inside facing the sausage material, has a coating of 
polyvinylchloride and on the outside is coated with viscose. The coated 
cellulose layer expands when it becomes moist and then shrinks once again 
on drying. When this happens the shrinkage stresses that occur can be so 
great that the sausages will burst if not handled carefully and properly. 
Compared to the production of a single-layer extruded thermoplastic 
sausage skin the production of a cellulose fibre casing is extremely 
complex and costly. 
German Pat. No. 23 58 560 describes the production of a two-layer sausage 
casing, for table and boiled sausages, having an inner layer, for example, 
of polyamide 12, and an outer layer of polyamide 6, in which regard the 
outer layer is subjected to acid treatment. This acid treatment increases 
the water-absorption or swelling capability of the outer layer and at the 
same time increases the shrinkage that occurs on drying. The combination 
of a markedly swellable and thus shrinkable outer layer with an inside 
layer that is impermeable to water results in dry shrinkage of the outer 
layer to a casing that lies tightly against its contents. In practice it 
has been shown, however, that the shrinkage stress of the acid-treated 
swellable polymer layer, which can be induced by drying, is insufficient. 
The acid treatment also reduces the mechanical strength of the outer 
layer. 
A variation of the sausage casing according to German Pat. No. 23 58 560 is 
described in German Pat. No. 27 24 252. In place of polyamide 6 that can 
be rendered swellable by acid treatment a mixture of polyamide 6 with 
preferably 5 to 20% polyvinyl alcohol is used as the outer layer. These 
casings are said to have a very low oxygen permeability and fit tightly 
once the sausage material has cooled; however, they have not yet been 
adopted for practical use and are not commercially available. 
German Pat. No. 28 50 182 was the first to describe a sausage casing that 
encloses the sausage material closely and without wrinkling without the 
need of any additional processing and without any need for recourse to a 
two-layer structure. This involves a shrinkable multiaxially stretched 
thermally fixed sausage casing of polyamide, the glass point of which 
shifts dependent on reversible water absorption down to minus 
temperatures. Because of this, the casing after boiling and when rinsed 
off can match the contraction of the sausage material caused by shrinkage 
and thus remain close fitting. 
This casing makes possible a considerable improvement with regard to 
tightness and freedom from wrinkles; however, the casings require 
improvement in that they do not display sufficient resistance to tearing 
in all areas of application. Thus it can sometimes happen that when the 
full sausage is being cut longitudinally the casing can burst. If one 
attempts to peel the sausage casing off spirally, in the usual manner, 
i.e., if one attempts to remove a strip of specific width from a prepared 
slice in a circumferential direction, it is frequently impossible. More 
often than not the strip-off direction will continue in the longitudinal 
direction of the sausage. Finally, the resistance to tearing of the casing 
plays a large role in the case of vacuum-packed sausages particularly with 
regard to large-diameter boiled and table sausages. It is preferred that 
today's boiled and table sausages be packed in half diagonal slices, in 
order to permit the customer the opportunity to make a visual inspection 
of the goods. During the vacuum packing of sausage that is sliced 
diagonally, the air that is always contained in porous coagulated sausage 
material expands considerably on account of the reduced external pressure 
thereby straining the casing, particularly in the peripheral direction. A 
casing that has become marred by a small longitudinal split during the 
slicing process will thus tear during the vacuum packing in the event of 
inadequate resistance to tearing, in some cases starting at the location 
of the damage, parallel to the longitudinal axis, right up to the tip of 
the sausage. 
In addition to the foregoing, it is also desirable that the customer be 
offered a dull sausage casing since the classical sausage casings of 
natural intestinal membranes as well as casings of cellulose fibre have 
exceptionally dull surfaces. For this reason the customer will from time 
to time assume that only low-quality sausages are packed in shiny 
artificial casings. 
According to German Pat. No. 28 50 181 an improvement in resistance to 
tearing is achieved in that instead of the polyamide that is used in 
German Pat. No. 28 50 182, the glass point of which can be shifted to low 
temperatures depending on water absorption, a polymer mixture of these 
polyamides and modified polyamide-compatible polyolefins, for example, an 
ionomer resin, is used for the production of the sausage casings. It is 
obvious that it would be desirable to be able to achieve such an 
improvement in resistance to tearing and also achieve a matt surface 
without using any additives, and thus without using a polymer blend. 
Thus it is the task of the present invention, proceeding from the tubular 
film according to German Pat. No. 28 50 182, to improve that tubular film 
to the point that it can be cut without tearing, peeled spirally, vacuum 
packed when sliced and at the same time has a matt appearance. 
This task is solved by a tubular film that consists of a polyamide that can 
absorb at least 5% of its weight in water up to saturation and displays 
the following elastic behaviour: 
At room temperature, when saturated with water, at an internal pressure 
between 0 and 0.6 bar according to the equation .DELTA.D=m.times.p+c, it 
will expand cylindrically and evenly according to internal pressurization 
line (1) and when the internal pressure is released to between 0.6 and 0 
bar according to the equation .DELTA.D'=m'.times.p+c', it will contract 
cylindrically and according to internal pressure release line (2) wherein 
.DELTA.D is the difference in diameter expansion in (mm) during internal 
pressurization 
.DELTA.D' is the difference in diameter contraction in (mm) during internal 
pressure release 
m is the upward slope of the internal pressurization line (1) of a plot of 
.DELTA.D vs internal pressure 
m' is the upward slope of the internal pressure release line (2) of a plot 
of .DELTA.D' vs internal pressure 
p is the internal pressure in (bar) 
c is the ordinate sector of the internal pressurization line (1) (c is 
always=0) 
c' is the ordinate sector of the internal pressure release line (2) and the 
following limiting conditions apply: 
1. The absolute values for m and m' lie between 23 and 6, preferably 
between 20 and 8, and especially between 17 and 11; for a given diameter 
the values for m and m' vary by no more than 20%, preferably by not more 
than 11%. 
2. c' is always less than 4.5 mm, preferably less than 2.5 mm and 
especially less than 1.5 mm. 
3. Equations (1) and (2) apply in the internal pressure range between 0 and 
0.6 bar, respectively. 
The equations that define the elasticity of the tubular film according to 
the present invention, together with their limiting conditions, are 
derived from the following mesurements: 
Sections of a tubular film according to the invention, 50 cm long, were 
sealed hermetically at one end and softened for one hour in water at a 
temperature of approximately 20.degree. C. Subsequently, the open end of 
the section was connected to a source of compressed air that was fitted 
with a sensitive pressure gauge and then pressurized from 0 to 0.6 bar in 
steps of 0.1 bar. For each pressure increment p the difference in diameter 
.DELTA.D was measured by means of calipers. Once 0.6 bar had been reached 
the values for p and .DELTA.D were measured in the reverse sequence. These 
measurements were repeated with several sections in order to obtain 
statistically reliable data.

In FIG. 1, it is not difficult to see that the internal pressurization line 
(1) and the internal pressure release line (2) differ very little from 
each other either in relation to their slopes m and m' or in relation to 
their ordinate sectors c and c'. 
Accordingly, the tubular film according to the invention withstands high 
internal pressurization of this sort without any significant irreversible 
stretching in the circumferential direction of the casing. Measurements 
have revealed that when the casing is being filled internal pressures of 
between 0.35 and 0.6 bar can occur routinely. 
Accordingly, the casing according to the invention can be expanded like a 
spring and has sufficient recovery so that it will fit closely and without 
wrinkles after the heat-treated sausage has cooled down. 
Thus the recovery corresponds to the diameter expansion difference .DELTA.D 
and the spring constant of the slope m of the internal pressurization line 
(1). 
It has been demonstrated that only those tubular films in which the 
above-cited limiting conditions for m, m', p, c and c' are within the 
quoted ranges can satisfy the demands for freedom from wrinkles and proper 
slicing or vacuum packing, respectively. 
If m is less than 6, the filling pressure, for example, will be 
insufficient to ensure sufficient recovery to guarantee freedom from 
wrinkles. In this case, the "spring" is too stiff. On the other hand, if m 
is greater than 23 it will no longer be possible to expand the casing 
cylindrically and regularly during the filling process. Partial bulges 
will occur. The "spring" is then too soft. 
In the event of clear differences between m and m' for the same casing, or 
for c' values that are greater than 4.5 mm, respectively, the casing is no 
longer dimensionally stable. It will then become permanently stretched 
during the filling process, and will no longer be wrinkle-free. 
In a preferred version the tubular film is of a polyamide that can 
crystallize in the .alpha.-form. 
Examples of polyamides having a minimum water absorption capability of 5% 
at room temperature in the water-saturated state are polycaprolactam (PA 
6), polyhexamethylenedipamide (PA 66), and copolymers and mixtures 
thereof. Of these, polycaprolactam and polyhexamethyleneadipamide are 
especially preferred. The foregoing polyamides all crystallize in the 
.alpha.-form. 
The preferred wall thickness of the tubular film amounts to 60 to 100 
.mu.m, particularly 65-80 .mu.m. This has a bursting strength of at least 
0.8 bar (at room temperature and at a relative humidity in the range of 
35-75%). 
The tubular films according to the invention are produced by extrusion of a 
primary tube of polyamide and subsequent simultaneous multiaxial 
stretching, characterized in that the primary tube of polyamide, that can 
absorb up to 5% water, is completely fixed thermally after multiaxial 
stretching during controlled multiaxial contraction. 
The second process stage, multiaxial stretching, is completed by 
conventional methods, in which, of course, specific minimal stretch 
conditions in the longitudinal and transverse directions are met or 
exceeded. The longitudinal stretch ratio is at least 1:2.3 to 1.4, 
preferably 1:2.7 to 1:2.9, the transverse stretch ratio at least 1:2.5 to 
1:4.5, preferably 1:3 to 1:3.5. 
The wall thickness of the tubular film that is obtained according to the 
multiaxial stretch process, should be not less than 30, preferably 35 
.mu.m. 
In relation to the dimensions of the tubular film after stretching in the 
longitudinal and the transverse directions, the controlled multiaxial 
shrinkage in the course of thermal fixing should amount to at least 15%, 
in which connection shrinkage in the order of 20% can serve as a 
benchmark. As a rule, shrinkage does not exceed 40%. 
Controlled shrinkage and complete thermal fixing can be undertaken in one 
stage, according to one exemplary version of the process of the invention. 
In this case, controlled shrinkage and complete thermal fixing are 
effected in one heat treatment lasting at least 20 seconds. The duration 
of the heat treatment depends on the reaction temperature, the higher the 
temperature, the shorter the duration. As a general rule, treatment 
durations of 240 seconds will suffice. According to one version of the 
process of the invention the heat treatment can be undertaken using hot 
water, steam or heated hydrated polyhydric alcohols, preferably glycerin 
or propylene glycol. If alcohols are used these preferably contain at 
least 10% water. The temperature of such a heat transfer medium is at 
least 90 or, at a maximum, 150.degree. C. Alternatively, the heat 
treatment can be undertaken by means of hot air, a heated inert gas, 
preferably CO.sub.2 or nitrogen, or by means of infrared irradiation, 
preferably that which is emitted by IR radiators of medium wavelengths, at 
temperatures of not less than 180.degree. C. Here, too, the duration of 
the heat treatment will be at least 20 seconds. The upper limit for the 
duration of the heat treatment and the treatment temperature are critical 
only so that no damage to the plastic that makes up the film may occur. 
Accordingly, at higher treatment temperatures the duration of the 
treatment can be shorter. Treatment temperatures of 320.degree. C. 
radiator temperature for the IR radiator or an inert gas, respectively, 
are not to be exceeded. It is preferred that the thermal fixing medium, 
hot air or protective gas, be blown turbulently against the tubular film. 
If shrinkage and thermal fixing are undertaken by using IR irradiation, it 
is preferred that this be done in an oven fitted with IR radiators. 
According to yet another variation of the process of the invention, 
controlled shrinkage is permitted after the multiaxial stretching, 
initially by the application of heat and then thermal fixing is completed 
in a separate stage while maintaining the dimensions of the tubular film 
that were obtained after shrinkage. In this regard, it is preferred that 
higher temperatures are used for the thermal fixing than are used for the 
shrinkage process. 
The same shrinkage conditions apply for this two-stage method of operation 
as in the one-stage method, i.e., at least 15% shrinkage in the 
longitudinal and the transverse directions. Controlled shrinkage is 
effected in the presence of hot water or steam at a temperature of at 
least 90.degree. C. (the upper limit is preferably 100.degree. C.), 
whereas thermal fixing is then effected in a separate stage, using hot 
air, a protective gas, or IR irradiation. The first stage in the two-stage 
method of operation, i.e., the controlled shrinkage, preferably carried 
out in the presence of hot water or steam, requires a treatment duration 
of at least 20 seconds, preferably 30 seconds, at a minimum temperature of 
90.degree. C. For the second stage, completion of the thermal fixing, the 
treatment time will depend, as in the other cases, on the temperature of 
the medium. The latter should not be below 180.degree. C. As a rule, a 
treatment time of 3, preferably at least 5 seconds, will be required. 
Thus, when IR irradiation is used at a temperature of between 180.degree. 
and 320.degree. C., a treatment time of 3 to 10 seconds will be required. 
The tubular film can be either straight or curved in the manner of a 
circular sausage skin. 
As a result of the multiaxial stretching the tubular film according to the 
invention has a dull surface. This desired effect was obtained quite 
unexpectedly. 
A further surprising effect of the tubular film according to the invention 
lies in the fact that despite a total lack of shrinkage at under 
90.degree. C., it can contain cooked and boiled sausage, cooked between 
70.degree. and 87.degree. C. and whose diameter when being filled expands 
expediently between 5 and 15%, so that it is completely unwrinkled, even 
after it has cooled down. Up to now, it had been accepted that only 
shrinkable plastic casings could contain heat-treated sausage without 
wrinkling after cooling. 
The invention will be explained on the basis of the following examples 
without restriction of the scope thereof. 
EXAMPLE 1 
Pure commercial polycaprolactam (having a relative viscosity of 4, measured 
in 1 g granulate, dissolved in 100 ml 96% sulfuric acid at 25.degree. C.) 
was plasticized in a single cam extruder at 260.degree. C. and extruded 
through an annular nozzle to form a primary tube 34 mm in diameter and 
with walls 0.45 mm thick, and then consolidated by cooling. 
Subsequently, the primary tube was warmed to 85.degree. C. and 
simultaneously stretched multiaxially with the help of a secondary blower. 
This resulted in the following stretch ratios: 
Lateral stretch ratio 1:3 
Longitudinal stretch ratio 1:3 
Wall thickness taper 9:1 
Thus was obtained a multiaxially stretched tubular film of 102 mm diameter 
having a wall thickness of 0.050 mm, the surface being very shiny and 
which had high shrinkage. 
In the subsequent third stage of the process the film was thermally fixed 
to be multiaxially stretchable with the help of a tertiary blower whilst 
permitting lateral shrinkage of 21% and longitudinal shrinkage of 19%, 
relative to the dimensions of the multiaxial stretched tubular film, by 
treatment with hot water at 90.degree. C. for 35 seconds. Thus was 
obtained a tubular film according to the invention, having a diameter of 
80-81 mm and having a wall thickness of 0.070 mm. 
Finally, the tubular film was dried and whilst retaining its last 
dimensions it was passed for 5 seconds through an oven fitted with medium 
wavelength IR radiators and heated to 212.degree. C. and thereby totally 
thermally fixed. It was then cooled, flattened, and rolled. 
The film so obtained could not be shrunk at under 90.degree. C. The outside 
was now dull and resisted tearing to the extent that it could be made into 
sausage casing, filled with raw sausage material, boiled and cooled, cut 
neatly, and effectively vacuum packed in halved form (see Table later 
herein). 
In addition to the foregoing the tubular film contained the cooled cooked 
sausage without wrinkling when, during the filling process, it was 
expanded by some 10% to a diameter of 88-89 mm. Its elastic behaviour 
according to the invention is shown in FIG. 1. 
EXAMPLE 2 
Whilst maintaining all the conditions set out in Example 1 and using 
polycaprolactam as the molding material, a multiaxially stretched tubular 
film was produced that was treated with saturated steam at 100.degree. C. 
instead of with water in the third stage of the process. The following 
stages were exactly the same as those in Example 1. The tubular film 
according to the invention, which was produced by this variation of the 
process, displayed the same characteristics as the tubular film produced 
as in Example 1. 
EXAMPLE 3 
Using the same polycaprolactam as in process stage 3, the same procedure 
was followed as in Example 1. The controlled shrink thermal fixing was 
however carried out by using gylcerine instead of the treatment involving 
hot water; the glycerine that was used contains 14-15% water and was 
heated to 120.degree. C. The time involved was 40 seconds. The same shrink 
values were permitted as in Example 1. Subsequently, the tubular film was 
cleansed of glycerin by being sprayed with water, dried, laid flat, and 
rolled. 
The film was already totally thermally fixed, so that it was possible to 
dispense with treatment in the IR radiator oven. The film produced in this 
example displayed the same characteristics as the films obtained in 
Examples 1 and 2. 
EXAMPLE 4 
Pure commercial polyhexamethyleneadipamide (PA 66) having a relative 
viscosity of 3.6 (measured in 1 g granulate, dissolved in 100 ml 96% 
sulfuric acid at 25.degree. C.) was plasticized in a single cam extruder 
at 280.degree. C. and extruded through an annular nozzle to form a primary 
tube of 34 mm diameter and with a wall thickness of 0.45 mm, and then 
consolidated by cooling. 
The primary tube was simultaneously multiaxially stretched after being 
warmed to 95.degree. C. The following stretch ratios were used when this 
was done: 
Transverse stretch ratio 1:3.2 
Longitudinal stretch ratio 1:2.8 
Wall thickness taper approximately 9:1 
This resulted in a highly stretched tubular film of approximately 109 mm 
diameter and having a wall thickness of 0.050 mm. This film was then 
treated with a tertiary blower with hot water at 95.degree. C. for 35 
seconds, in which regard a longitudinal shrinkage of 19% and a transverse 
shrinkage of 21% were permitted. 
A tubular film was obtained that had a diameter of 86 mm and a wall 
thickness of 0.070 mm. 
Subsequently this was passed on for thermal fixing in the inflated state 
with retention of its last dimensions and passed for 5 seconds through an 
IR oven at 235.degree. C., totally thermally fixed thereby and finally 
cooled, laid flat and rolled. 
The polyhexamethyleneadipamide film according to the invention that was 
produced by this method did not shrink at below 90.degree. C., had an 
extremely dull outside surface, and was so tear resistant that it could be 
cut neatly and properly vacuum packed in halved form (see Table later 
herein). 
Furthermore, it contained cooled cooked sausage without wrinkling when it 
was expanded by approximately 7% to a diameter of 92 mm during the filling 
process. Its elastic behaviour according to the invention is shown in FIG. 
2. 
Comparative Example 1 
The same polycaprolactam as in Example 1 was extruded and multiaxially 
stretched under the conditions given for Example 1. 
Departing from the process according to the invention, the tubular film was 
thermally fixed for 8 seconds by inflation with hot air at 160.degree. C. 
and with retention of its stretch dimensions (thus without any 
longitudinal and transverse shrinkage and because of this without any 
increase in wall thickness), cooled down, laid flat, and rolled. 
A tubular film was obtained having a diameter of 102 mm and a wall 
thickness of 0.050 mm. It was immersed in warm water at 78.degree. C. and 
shrank 16% transversely and 18% longitudinally within 2 seconds. It had a 
very shiny outer surface, could not be cut so neatly or vacuum packed in 
halved form in the same way as the casings in Examples 1 to 4 (see Table 
later herein). 
Comparative Example 2 
Polyamide 6.9, that preferably forms crystals in the .gamma.-form and 
absorbs only 3% water when in the water-saturated state at room 
temperature, and having a relative viscosity of 3.3 (measured on 1 g 
granulate in 100 ml 96-% sulfuric acid at 25.degree. C.) was plasticized 
in a single cam extruder at 225.degree. C. and extruded through an annular 
nozzle to form a primary tube 34 mm in diameter and having a wall 
thickness of 0.45 mm; this was then consolidated by cooling. 
Subsequently, this primary tube was treated in exactly the same manner as 
in Example 1 according to the invention, in which connection all the 
process parameters remain the same as in Example 1. 
A polyhexamethylenenonanamide tubular film was obtained that did not shrink 
below 90.degree. C., had a relatively dull outside surface, and met all 
requirements with regard to neat slicing and proper vacuum packing but 
which, as can be seen from FIG. 3, was so stiff that it could not contain 
cooked sausage without wrinkling (m-value too low). 
Furthermore, this casing, while it preferably formed crystals in the 
.gamma.-form and not in the .alpha.-form remained more easily deformed 
during the boiling process than the casings according to the invention. 
The elasticity of this PA 6.9 casing that was too small as a consequence of 
inadequate water absorption capacity (less than 5%) at room temperature 
when in the water saturated state. ;p The following table shows the 
criteria that are important from the standpoint of the invention, on the 
basis of the examples. 
TABLE 
__________________________________________________________________________ 
(3) 
(1) First 
(4) 
Water (2) Cutting 
Vacuum 
(5) 
Molding 
Absorption 
Crystal 
Surface 
Certainty 
Packing 
Wrinkle 
Examples/Characteristics 
Mass (%) Shape 
Lustre 
(%) Safety 
Formation 
__________________________________________________________________________ 
Example 1 PA 6 11 .alpha. 
11 92 196 No wrinkles 
(according to invention) 
Example 4 PA 6,6 
9 .alpha. 
9 96 196 No wrinkles 
(according to invention) 
Comparative Example 1 
PA 6 11 .alpha. 
35 47 94 No wrinkles 
Comparative Example 2 
PA 6,9 
3 .gamma. 
18 87 180 Wrinkles 
__________________________________________________________________________ 
(1) Water absorption (%) at room temperature by storing in water until 
saturated. 
(2) Surface lustre measurement as per DIN 67530 angle of incidence 60 
degrees; standard light C (artificial daylight), 100 deg. scale. 
(3) First cutting certainty (%) established by cutting 100 cooled cooked 
sausages with a knife sharpened to conventional trade standards. Data are 
the number of cooked sausages that can be cut without damage to the 
sausage casing in the longitudinal direction. 
(4) Vacuum packing safety: the sausage halves obtained after the cutting 
test (200 in each instance) were vacuum packed in a commercial `Autovac* 
Type AVQ` from Framer and Grebe W. Germany with the manometer at the stop 
(100% vacuum). The table quotes the number of sausage halves that 
underwent the test without longitudinal splitting of the casing as far as 
the tip. 
(5) Assessed visually after the cooked sausage has cooled down (100 in 
each case). Plain longitudinal wrinkles were formed only in Comparative 
Example 2. 
*Trade Mark