VISCOSITY-PLASTICITY MEASUREhlENTS OF T H E EFFECT OF GELATIK OK ICE-CREAM SIIXES BY FLOYD ERVIS KCRTZ*
Xumerous methods of testing gelatin are known. Dahlberg, Carpenter and Hening‘ have reviewed and criticized, in the light of their own researches, some of the more important. It is the purpose of this paper to consider the significance of basic viscosity-plasticity measurements in grading gelatin for the manufacture of ice cream
Experimental For the purpose of this report equal concentrations of six commercial gelatins were used in making ice-cream mixes of the following formula: Milk-solids-not-fat Fat Sucrose Gelatin Water
10%
12%
14% 0 25%
63 i s %
Another mix was made identical, except that no gelatin was added. After the mixes had stood for 24 hours a t the same temperature (approximately oT.) measurements were made to determine the basic viscosity of each. Leighton and Kurtz2 discuss the appropriateness of the term “ basic viscosity” as applied to the values obtained from these measurements. They also describe the method of making these measurements, which consists, briefly, in beating out the structure of the ice-cream mix at o°C. until a constant value is obtained when the sample is drawn through a calibrated pipette by a constant vacuum pressure. The dimensions of this 8.2 cc. pipette have been recorded. Table I expresses in centipoises the values obtained for the basic viscosity of the seven mixes. Fig. I shows graphically the relationship between the viscosities of these mixes. After standing 48 hours a t 0°C. other samples of the same mixes were measured for plasticity. The method used in making these measurements was the same, with one exception, as that used in measuring the basic viscosity - the exception being that, instead of beating out the structure, precautions were taken that it should be broken only by the passage of the material through the plastometer. Table I1 and Fig. 2 show the results of these measurements. The consistencies are tabulated in centipoises and the yield values in dynes. * Research Laboratories, Bureau of Dairy Industry, U. S. Department of Agriculture. 1
Dahlberg, Carpenter and Hening: Ind. Eng. Chem., 20,516 (1928). J. Phys. Chem., 33, 1485,(1929).
I490
FLOYD ERVIN KURTZ T.4BLE
1
Variation of basic viscosity of ice cream mixes with different grades of gelatin Gelatin sample
Shearing force
No.
dynes 1.
2.
No gelatin
3, 4. 5.
446.7 562.8 653.4 775.8 886.3
Volume delivered
cc. per sec. I .
2.
3. 4. 5. I .
2.
I
3. 4.
5. 1. 2. 2
3. 4.
5. I .
2.
3
3. 4. 5. 1. 2.
4
3. 4. 5. 1. 2.
5
3' 4. 5. I. 2.
6
3. 4. 5.
446.7 562.8 653.4 775.8 886.3 446.7 562.8 653.4 775.8 886.3 446.7 562 . a 653.4 775.8 886.3 446.7 562.8 653.4 775.8 886.3
446.7 562.8 653.4 775.8 886.3
I.
-
,2932 ,3470 ,4001 ,4556
,1895 .2253 ,2637 ,3035 .I929
3. 4.
,2299
5'
'3063
I .
3' 4. 5. I. 2.
3. 4.
centipoises
19.43
29.41
-
2.
2.
Basic viscosity
29,34
,2662
-
37.52
.2082
-
,3169
24.65
j.
I. 2.
3' 4. 5. I .
2.
,3530
21.93
,4070
,2016
3. 4. 5 . ,3185
28 . O I
EFFECT OF GELATIN ON ICE-CREAM MIXES
1491
TABLEI1 Variation of the consistency and yield value of ice cream mixes with different grades of gelatin Gelatin sample NO. I . 2 .
No gelatin
3. 4. 5. I. 2.
I
3' 4. 5. I.
2
3
2. 3. 4.
Yield value
dynes
cc. per sec.
centipoises
dynes
446.7 562.8 653.4 775.8 886.3
I.
19.71
20
39.63
35
39.67
125
55.03
170
25.23
75
25.03
20
30.37
115
446.7 562.8 653.4 775.8 886.3 446.7 562.8 653.4
775.8
I.
446.7 562.8 653.4 775.8 886.3
2. 3. 4. I. 3. 4. 5. 1. 2.
3. 4. 5. I. 2.
6
Consistency
886.3
2 .
5
Volume delivered
5.
5.
4
Shearing force
3. 4. 5.
446.7 562.8 653.4 775.8 886.3
2 .
3. 4. 5. I. 2.
3' 4. 5. I .
2. 3. 4. 5. I.
2.
3' 4. 5. I. 2 ,
3' 4. 5.
,2167 ,2724 ,3213 ,3807 ,4422
.1338 -
,1865 .z164
,1121
,1344 ,1615 .I933
.07168 ,1079 ,1311
'1954 ,2769 .3238
-
446.7 562.8 653.4 775.8 886.3
2 .
.2202
3' 4. 5.
,3029 ,3485
446.7 562.8 653.4 775.8 886.3
2. 3' 4. 5.
I.
I.
.2r87
'2558
FLOYD E R V I S KURTZ
S\iearing Force
in
Dynes
FIG. I
u v)
i h e a r i n q F o r c e in D y n e s
Fro
2
EFFECT OF GELATIN O N ICE-CREAM MIXES
I493
Discussion Previous tests, for the most part, have failed to discriminate between the effects produced by different gelatin samples on the various fundamental physical properties of the ice-cream mix. The method employed, as a rule, has measured either the effects on one to the exclusion of those on the other physical properties of the mix, or the resultant value of the combined effects on several of the basic characteristics of the mix. I n so far as the various fundamental physical properties of a mix may differently affect the manufactured product, it would be desirable in the test to be applied to the mix to differentiate these properties. In this investigation measurements have been made to determine the effects produced by equal concentrations of different gelatins, in otherwise identical ice-cream mixes, on the basic viscosity, consistency, and yield value. hlore research will be necessary to correlate these basic values of the mix with the quality of the frozen ice cream. As this correlation is achieved, such measurements as have been made in this study will be of value in obtaining the desired qualities in the manufacture of ice cream for, as references to Figs. I and 2 will show, a considerable variation can be obtained not only in the quantitative,measure of any one, but also in the relation to each other of the three properties here measured. Basic viscosity quite likely affects the growth of ice crystals in the freezer. Since the beaters furnish many nuclei for crystallization, an increased basic viscosity of the mix would serve to hinder the growth of these crystals. Dahlberg, Carpenter and Hening's* data on gelatins indicate that there is no relation between basic viscosity of mix and overrun. From a slightly different standpoint, however, Leighton and Williams' found that overrun per unit time is considerably affected by the basic viscosity and seems to bear an inverse relation to it. In the gelatin mixes, which are known to have a gel structure, the yield value should be interpretable as the force necessary to break this structure. On this hypothesis, then, the yield-value is a measure in an absolute unit, t,he dyne, of the structural strength produced in the mix by the gelatin. In reality, a correction is necessary. This is due to the slight structure of the ice-cream mix not dependent upon the presence of the gelatin. Reference to Fig. 2 will show that the non-gelatin mix has a yield-value of 20 dynes; so, if this were subtracted from each of the values obtained for the gelatin mixes, there would be obtained an absolute measure of the structural strength due to the presence of the gelatin. After sufficient force is applied to a mix to break down its structure and establish flow through the capillary, the volume delivered per unit, time as a function of the total force applied minus the yield-value gives a linear graph of the consistency, which can be considered analogous to the viscosity of a truly viscous substance.
* LOC.cit. 1
J. Phys. Chem., 33, 1481 (1929).
I494
FLOYD E R V I S KURTZ
The effect of the consistency of the mix on the frozen ice cream is not known and indeed is difficult even to conjecture. It is possible that gumminess may depend upon the consistency of the mix, although this is, by no means, certainly known. Further researches quite possibly will reveal relations unseen a t present. Concerning the relation between yield-value and the properties of the frozen ice cream: I t is rather generally accepted that the structure of an ice-cream mix during the hardening period obstracts the growth of ice crystals and, in this way, influences the smoothness of the product Likewise, structure should have an inhibitory influence on the crystallization of lactose or sucrose. By preventing collapse of the frozen product, structure prevents loss from dipping and also preserves the dispersion of the air phase, thus preventing the development of sogginess.
Conclusion It is theoretically plausible that basic viscosity, consistency, and yieldvalue of the mix have individually peculiar relationships to the properties of the frozen ice cream. A correlation of the values of these physical measurements with the nature of the manufactured ice cream will depend, for the most part, on future research. As this correlation is developed, the value of the combined basic viscosity-plasticity measurements for grading gelatin used in ice cream manufacture will be twofold: I . Values are obtained in fundamental physical units; 2 . In as far as these basic physical properties of the mix affect differently the properties of the frozen ice cream, their individual measurement would better enable the operator to control the properties of the manufactured product.
Summary To determine basic viscosity, yield-value, and consistency, measurements have been made on seven ice-cream mixes, six of which, otherwise identical, contained equal concentrations of different commercial gelatins, and one of which contained no gelatin. The results are tabulated. 2. The value of these measurements in grading gelatins for ice cream manufacture is discussed. I.
