System for measuring the crispiness of materials

A device and a method for the determination of a Fractal number representative of the crispiness and crunchiness of various materials, especially edible materials. The material to be tested is crushed by the application of a given force by a piston moving in a cylinder, which crushes such substance, whereby noise is created, recorded and subsequently evaluated. A preferred device comprises a microphone positioned beneath a baseplate in the cylinder of the device, on which plate the sample is positioned, which microphone picks up the noise which is subsequently evaluated. According to a preferred embodiment an opening is provided in the cylinder for inserting and removing the sample to be tested.

FIELD OF INVENTION 
The invention relates to a device and to a method for the determination of 
the crunchy properties of various substances, and especially of edibles. 
The device and the method are based on the gradual crushing of the tested 
substance, while the noise created thereby is sensed by voice sensor such 
as a microphone and evaluated. 
The device of the invention can be attached as attachment to conventional 
machines, which are on the market, such as Instron, JJ, Lloyd, etc., which 
are used to determine mechanical properties of solid foodstuffs and other 
materials. 
Amongst others there can be evaluated the freshness of products like 
cereals, waffles, snacks, noodles and similar products, sugar cubes, etc. 
The device comprises a generally cylindrical body in which there is located 
a base plate on which the material to be tested is supported, and adjacent 
or below which there is positioned a microphone, which is protected by 
said base plate. There is provided a piston which moves inside said 
cylindrical member, and which is moved downwards at a predetermined 
velocity and deformation rate. The piston exerts a certain pressure on the 
tested substance and while this is disintegrated, the noise created is 
picked up by the microphone. A voice card inserted into a computer serves 
to pick up the noise thus created and this is evaluated by means of a 
certain algorithm which generally provides a numerical result which is 
indicative of the crunchiness of the substance. This number is indicative 
of the "roughness" of the produce test. The measurement gives also an 
indication of the humidity of certain substances, and the higher such 
humidity, the greater the change in the noises picked up by the 
microphone. It is generally possible to obtain a linear curve between the 
degree of roughness and crispiness and the percentage of water content of 
the product. 
The device is illustrated with reference to the enclosed schematical 
Figure, which is not according to scale and in which 11 is a cylinder, in 
which piston 12 can move up and down, pressure being exerted on it by 
drive 13. There is provided at the bottom of the cylinder 11, a protective 
plate 14, on which the substance to be tested is placed. This plate 
protects microphone 15 which is suitably connected by wire 18 to convey 
noises originating from the crushing of the product being tested as it is 
disintegrated by such pressure, and evaluation is being done by computer 
means provided with a voice card. 
There is provided a base 16 which also serves as sound isolator and the 
cylinder 11 is surrounded by isolating sleeve 17. There is provided an 
opening in the cylinder 11 and isolating sleeve 17, which is closed by 
member 19 and 19' equipped with handle 20 for inserting and removing a 
sample which is placed on support plate 14.

The simple device has a wide application for many products and the above 
are but a few samples of these. 
The procedure we followed to derive the fractal dimension (fractal number) 
of the acoustical graphs is as follows. The experimental curve Y(x), where 
Y is the noise amplitude and x is the time is fitted ("smoothed") by, for 
example a polynomial model and then transformed into a normalized 
relationship R(x) where the dimensionless parameter R(x) has been defined 
by A. M. Barrett et al, 1992. 
EQU R(x)=Y(x)-Y*(x)!/Y*(x) 
Y*(x) being the corresponding fitted value at x. 
The apparent fractal dimension of the rugged line R(x) can then be 
determined using the "Blanket alogarithm", which has also been used in the 
characterization of rugged surface textures. The creation of successive 
layers of the "blanket" filling the "valleys" at each iteration is 
achieved using the equation: 
EQU B.sub.n+1 (l)=max {B.sub.n (i).div.1, max B.sub.n (i-1), B.sub.n (i+1)!} 
where B (i) is the blanket's half thickness at location x=i and n the 
iteration number, i.e. n=1, 2, 3. . . 
This equation is based on S. Peleg et al., 1984. 
A corresponding Richardsom plot can be produced by calculating the line's 
length at each iteration from the cumulative "blanket area", A(n), divided 
by its corresponding thickness. The line's length at each iteration is 
therefore defined as: 
EQU L(n)=A(n)/2n 
The fractal dimension D of R(x) is calculated by 
EQU D=1+.vertline.tag .delta..vertline. 
where tag .delta. is the slope of the linear portion of the log-log plot of 
the line's length L(n(! vs the blankets half thickness (n). 
REFERENCES 
A. M. Barrett, M. D. Normand, M. Peleg, E. J. Ross: Characterization of the 
jagged stress-strain relationships of puffed extrudates using the fast 
Fourier transform and fractal analysis. Food Sci. 53, 227-232, 235 (1992). 
S. Peleg, J. Naor, R. Hartley, D. Avnir: Multiple resolution texture 
analysis and classification. IEEE. Trans Pattern Anal. Mach. Intlligence. 
6, 518-523 (1984). 
The invention is illustrated by way of example with reference to the 
following Examples: 
EXAMPLE 1 
Dry sugar cubes were crushed, which had a solid content of about 97.95% on 
the average. Humidity of 1%, 2%, 3%, 4% and 8% was added. The cubes were 
crushed in an Instron tester to which there was attached a device 
according to the invention. Acoustic recordings were obtained and 
registered, which are attached herewith. The "roughness" of the records 
was evaluated and it was found to decrease with an increase of humidity. 
The results are: 
______________________________________ 
Per Cent Fractal Maximum Force for Crushing 
Humidity Number kg/cm.sup.2 
______________________________________ 
0 1.32 25.7 
1 1.23 13.0 
2 1.19 7.5 
3 1.16 7.5 
4 1.13 7.4 
8 1.10 1.2 
______________________________________ 
EXAMPLE 2 
A similar measurement was made with croutons, having a starting water 
content of about 0.25%. To this there were added varying percentages of 
water, and the results were: 
______________________________________ 
Added Humidity 
% Fractal Number 
______________________________________ 
0 1.62 
1 1.39 
2 1.37 
3 1.33 
4 1.30 
8 1.18 
______________________________________ 
The "roughness" of the recording decreases with an increase of humidity. As 
stated above, the novel device can be used for similar determinations with 
a very wide spectrum of products. 
There is advantageously provided an opening, at the lower part of the 
cylinder, with closure means, for the rapid introduction and removal of 
samples.