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The Determination of Total Solids in Dairy Products by Drying with Forced Heated Air. I. Results with Milk, Skim Milk, Cream, Condensed Milk, Condensed Skim Milk and Evaporated Milk*
T H E D E T E R M I N A T I O N OF T O T A L S O L I D S IN D A I R Y P R O D U C T S BY D R Y I N G W I T H F O R C E D H E A T E D AIR. I. R E S U L T S W I T H MILK, SKIM MILK, CREAM, C O N D E N S E D MILK, C O N D E N S E D SKIM M I L K AND EVAPORATED MILK ~ C. W.
LIVAK
A~D
F. ft. DOAN
The Pennsylvania Agricultural J~xpe~'iment S~atio~, State College, Pa.
It is generally conceded that moisture determinations in biological materials must follow empirical procedures and this viewpoint is confirmed by Halvorson (1), who in 1937 published a thorough survey of methods recognized by the Association of Official Agricultural Chemists. He concluded that it is not possible to arrive at the absolute water content of agricultural products and that the only practical method of determining total solids or moisture is to define them in terms of the residue or loss resulting from drying the materials u n d e r definitely specified conditions of temperature, time, pressure and any other factors which influence the rate or degree of moisture loss. The Mojonnier methods (3) based on A.O.A.C. definitions (2) of total solids are generally accepted as satisfactory by the dairy industry. Not all laboratories can justify the cost of Mojonnier testers, however, and are forced to use the slower "Official Methods" or the less accurate indirect methods employing hydrometers. Moreover, in cases where only one or two samples are to be analyzed the Mojonnier tests can h a r d l y be called convenient inasnmch as considerable time is required for bringing the hot plates to the required temperatures. Thus, there is a need for a quick, accurate and inexpensive method for determining the total solids in dairy products, especially where only one or two samples are analyzed at one time. An instrument known as the " D i e t e r t Moisture T e l l e r , " originally designed for determining the moisture content of sand, coke, gravel, cinders, etc., has been f o u n d satisfactory for agricultural roughages (4, 5) and appeared to offer possibilities for the estimation of total solids in fluid dairy products. Consequently, its use for this purpose was subjected to detailed study and the results constitute the basis for this report. T H E ~' DIETERT :MOISTUI~E T E L h E R ' ' AND ITS USE
Briefly, the " D i e t e r t Moisture Teller," illustrated in figure 1, consists of an electric blower and heating element encased in the u p p e r portion of a tube which Germinates at the bottom in a flared enlargement. A removable pan (dishholder), the bottom of which is constructed of fine woven brass l~eceived f o r p u b l i c a t i o n A p r i l 16, 1945. A u t h o r i z e d f o r p u b l i c a t i o n on A p r i l 10, 1945, as p a p e r no. 1279 in the J o u r n a l Series of t h e P e n n s y l v a n i a A g r i c u l t u r a l E x p e r i m e n t S t a t i o n . 7]]
712
C.W.
LIVAK AND F. J. DOAN
screening, is held snugly against the flared end of the tube by means of a spring clamp. The tube contains an air diffuser and a thermometer located immediately over the pan. At the top of the upright panel, to which the mechanism is attached, an automatic timing dial and switch are placed. The dial is graduated in half-minute intervals from zero to 15. Thirty- and 60-minute timers are also available. A thermo-regulator is attached to the flared base of the tube at the right side and just above the pan. Temperature adjustments are made by merely turning a knurled knob.
Fro. 1. The Dietert Moisture Teller: A, dishholder; B, interval timer and switch; C, thermo-regulator; D, total solids dish. The instrument is manufactured by the H. W. Dietert Company, 9330 Roselawn Avenue, Detroit, Michigan.
In using the Dietert apparatus for drying samples of fluid dairy products for the purpose of determining the total solids, suitable sample dishes (Mojonnier solids dishes are satisfactory), a laboratory desiccator of proper size, and an analyticM balance are required. All precautions in the weighing of samples'and residues and in the handling and cooling of dishes, etc., customarily required in quantitative analysis must be observed. Preliminary adjustments of the thermo-regulator should be made. The
DETERMINATION
OIP T O T A L SOLIDS
713
apparatus is then turned on by moving the timing pointer past three on the dial. This starts the blower and sends current through the heating elements. When the thermometer shows that the air temperature has reached the desired point, the pan containing the centered dish (tared) and well-spread sample is inserted in the clamp ring. Then the timer is set for the interval of drying desired. The draft of heated air is directed evenly onto the sample, rapidly evaporating the moisture and carrying it out through the screen base of the pan or dishholder. When the set time has elapsed the blower and heat are automatically cut off. At this point the dish containing the dried residue from the sample should be promptly removed to a desiccator and allowed to cool to balance temperature for accurate subsequent weighing. METHODS AND PROCEDURE
Preliminary observations revealed that the " D i e t e r t ~oisture Teller" was capable of rapidly removing moisture from dairy products and producing an apparently dry residue. Three different units when operated at the same temperatures and time intervals gave closely agreeing weights of residues from various fluid dairy products when all variables were controlled. Efforts to use comparatively large samples and less expensive balances of the torsion type failed to give consistent results and it was found necessary to use an analytical balance with careful adherence to recognized analytical practices in weighing the dishes, samples and residues. The possibility of using smaller sample dishes and drying duplicate or triplicate samples in the apparatus simultaneously was thoroughly investigated but erratic results were obtained. This, however, does not preclude the pro.bability that satisfactory multiple drying units can be constructed uulizing the principle of forced, heated air. After preliminary work had shown the capabilities of the Dietert apparatus and had narrowed down the number of the variables, some of which are mentioned above, it was deemed necessary to study each product separately in order to determine the most suitable time and temperature of drying, the best quantity of sample, whether dilution of the sample is advantageous, the proper diameter of dish, etc. To do {his, a large number of determinations were made, varying one factor at a time and comparing results with the average o~ triplicate determinations made according to "Official Methods." Scrupulous care was exercised in all of the work to avoid any fortuitous influences and to assure that the results represented only the effect of the variable under consideration. Seven samples of milk varying in fat content from 3.7 per cent to 4.4 per cent were analyzed for total solids in triplicate using the method given in the Fifth Edition of "Official and Tentative !V~ethods of Analysis" (2) including the use of sand (optional) and an aluminum dish 75 ram. in diameter. These samples were then analyzed in triplicate by means of the " D i e t e r t
714
C. W .
L I V A K AND F. J .
DOAN
Moisture Teller," using 16 different combinations of drying intervals (10 to 25 minutes) and temperatures (100 ° to 125 ° C.) and employing both oneand two-gram gamples. The results were compared with the average of those obtained by the "Official Method." After a suitable temperature and drying interval had been selected for use with the Dietert apparatus three additional samples of milk were analyzed using triplicate dishes having diameters of 50, 65, 75, 90, 95 and 100 ram., respectively. Substantially the same method was utilized for verifying a satisfactory Dietert procedure for determining the total solids of fluid skim milk, light and heavy cream and plain condensed whole and skim milk using between 6 and 12 samples for each product and omitting the 100 ° C. temperature. In the case of the concentrated products the Dietert samples consisted of (a) one gram of product plus one ml. of water, (b) two grams of product and (c) two grams of the product diluted as required in "Official Methods" for evaporated milk. Following the establishment of what was considered a suitable Dietert procedure a limited number of samples of each of the products were analyzed in triplicate using this procedure and the results compared with the average of triplicate determinations made b y " Official Methods." For comparative purposes they were also analyzed in triplicate by the Mojonnier Method. The preliminary study using dishes of different diameters indicated that the 75-mm. dish gave more satisfactory results with most of the products and at least as satisfactory with all products than dishes of any other size. RESULTS
Milk Observations made oll the drying of milk samples with the Dietert Moisture Teller indicated that fairly satisfactory total solids results could be obtained with either a one-gram or a two-gram sample and at high temperatures for shorter drying periods or at low temperatures for longer intervals. Analysis revealed, however, that while average results might be similar, the larger sample and longer drying intervals gave more uniform and closely agreeing results. On the basis of this study the following procedure was deemed the most satisfactory of those tried and is suggested for use with the " Dieter t Moisture Teller." Procedure for milk. A flat-bottom dish of 75 ram. diameter is heated in the Dietert apparatus for at least 10 minutes during which time the temperature of the apparatus is checked and adjusted. It is cooled in a desiccator to balance temperature and weighed, with a suitable cover, using an analytical balance. Approximately two grams of well-mixed milk are then put into the dish and accurately and quickly weighed (weighing pipettes may be used). The milk is spread evenly over the dish and it is placed in
DETERMINATION
OF
TOTAL
715
SOLIDS
t h e c e n t e r of t h e p a n of t h e o p e r a t i n g D i e t e r t a p p a r a t u s i n a l ev el position. T h e t e m p e r a t u r e s h o u l d a g a i n be c h e c k e d a n d d r y i n g s h o u l d be c a r r i e d o u t f o r 20 m i n u t e s at 120 ° C. W h e n d r y i n g is c o m p l e t e d , t h e dish s h o u l d be i m m e d i a t e l y t r a n s f e r r e d to a l a b o r a t o r y d e s i c c a t o r u n t i l cool. I t is t h e n weighed, w i t h cover, a n d t h e w e i g h t of d r y r e s i d u e e x p r e s s e d as p e r c e n t of t o t a l solids. Confirmation of accuracy. T o t a l solids w e r e d e t e r m i n e d in t r i p l i c a t e in five s a m p l e s of m i l k u s i n g the a b o v e p r o c e d u r e a n d also t h e M o j o n n i e r M et h o d . T h e r e s u l t s w e r e c o m p a r e d w i t h t h e a v e r a g e r e s u l t s of t r i p l i c a t e TABLE 1 Accuracy of the selected Dietert procedure for determining total solids of fluid whole milk as judged by the results obtained with the "Official M e t h o d " and as compared with those found by the Mojonnier method Per cent T.S. ' ' Official ' ' 12.32 12.69 12.75 12.80 12.75
Results with Dietert apparatus Per cent T.S. 12.38 12.44 12.34 12.82 12.84 12.77 12.77 12.74 12.71 12.80 12.75 12.78 12.84 12.83 12.77
Variation from ' ' Official ' '
-
................................................ - 0.05
Per cent T.S. 12.38 12.35 12.36 12.73 12.76 12.71 12.87 12.87 12.91 12.76 12.81 12.79 12.77 12.71 12.67
+0.06 +0.12 + 0.02 +0.13 +0.15 +0.08 + 0.02 0.01 - 0.04 0.00 - 0.05 - 0.02 + O.O9 + 0.08 +O.02
Algebraic average ...................................... + 0.043 Arithmetical average ............................ _+0.059 Range
Results with/¢Iojonnier tester Variation from ' ~Official ' ' + 0.06 + 0.03 +0.04 + 0.04 + 0~07 + 0.02 + 0.12 + 0.12 + 0.16 -
ft.04
+ 0.01 -0.01 +0.02 - 0.04 -0.08 + 0.036 +_0.057
to
+ 0.15
- 0.08
to + 0.16
d e t e r m i n a t i o n s b y the " O f f i c i a l M e t h o d . " T h e c o m p a r a t i v e d a t a ar e s h o w n i n t ab l e 1. I t a p p e a r s t h a t t h e D i e t e r t a p p a r a t u s is c a p a b l e of g i v i n g t o t a l solids results, w i t h milk, w h i c h closely p a r a l l e l t h e a c c u r a c y of t h e M o j o n n i e r Method. T h i s a c c u r a c y is c o n s i d e r e d h i g h l y s a t i s f a c t o r y . Skim Milk
T h e e x p e r i e n c e w i t h fluid skim m i l k in v a r y i n g t h e t i m e a n d t e m p e r a t u r e of D i e t e r t d r y i n g , the size of s a m p l e a n d size of dish was p r a c t i c a l l y i d e n t i c a l w i t h t h a t of f lu id w h o le milk. C o n s e q u e n t l y , t h e s a m e p r o c e d u r e was sel e c t e d as b e i n g best s u i t e d to this p r o d u c t . T a b l e 2 shows t h e c o m p a r a t i v e a c c u r a c y a t t a i n e d e m p l o y i n g the D i e t e r t a p p a r a t u s a n d t h e M o j o n n i e r t e s t e r w i t h five s a m p l e s of fluid skim milk.
716
c.w.
L I V A K AND F. J . TABLE
DOAN
2
Accuracy of the selected Dietert procedure for determining total solids of fluid skim qnil~ as j u d g e d by the results obtained w i t h the "Official M e t h o d " and as compared with those fo~nd by the Mojo~nier method Per cent
Results with Dietert apparatus
T.S. ' ' Official ~~
Per cent T.S.
9.10
9.13 9.15 9.09 Lost 9.03 9.01 9.19 9.21 9.18 9.27 9.25 9.25 9.19 9.21 9.20
8.96
9.10
9.18
9.14
Results with Mojonnier tester
Varlation from ~' Official ' '
Per cent T.S. 9.16 9.18 9.15 8.98 8.99 8.98 9.13 9.12 9.11 9.24 9.24 9.24 9.10 9.13 9.11
+0.03 + 0.05 0.01 -
+0.07 + 0.05 + 0.09 +0.11 + 0.08 + 0.09 +0.07 + 0.07 + 0.05 + 0.07 +O.06
A l g e b r a i c a v e r a g e ................................... A r i t h m e t i c a l a v e r a g e ....................... R a n g e ....................................
+ 0.063 + 0.064 - 0.01 to + 0.11
Variation from ' ' Official ' ' + 0.06 + 0.08 + 0.05 +0.02 +0.03 + 0.02 +0.03 +0.02 +0.01 + + + -
0.06 O.O6 0.06 0.04 0.01 -0.03 -
+ 0.028 _ 0.039 - 0.04 t o + 0.08
Cream C r e a m s a m p l e s w e r e f o u n d to be s o m e w h a t m o r e difficult to d r y t h a n m i l k a n d s k i m m i l k samples. This was t r u e even of t h e Official m e t h o d . The TABLE
3
Accuracy of the selected Dietert procedure f o r determbning total solids of light cream as j u d g e d by the results obtained with the "Official M e t h o d " and as compared with those f o u n d by the Mojonnier method Per c e n t T.S. ' ' Official ' ' 28.06
25.96
26.08
27.27
Results with Dietert apparatus Per cent T.S. 28.06 28.10 28.03 26.11 25.97 Lost 26.23 26.12 26.05 27.21 27.49 27.18
I
Variation from ' ' Official ' ' 0.00 + 0.04 -0.03 + 0.15 +0.01 +0.15 + 0.04 -0.03 -0.06 + 0.22 - 0.09
A l g e b r a i c a v e r a g e ........................ + 0 . 0 3 6 A r i t h m e t i c a l a v e r a g e ............................. + 0 . 0 7 5 R a n g e ....................................................... - 0.09 t o + 0.22
Results with Mojonnier tester P e r cent
T.S. 28.02 28.05 Lost 26.14 26.08 25.96 26.16 26.16 25.87 27.33 Lost 27.43
V a r i a t i o n from ' ' Official' ' 0.04 -0.01
-
+ o.18 +0.12 0.00
+0.08 +0.08 -0.21 + 0.06 +0.16 + 0.042 _+ 0 . 0 9 4 - 0.21 t o + 0.18
717
DETERMINATION OF TOTAL SOLIDS
s t u d y of v a r i a b l e s w i t h both l i g h t c r e a m (18.0 to 20.5 p e r c e n t f a t ) a n d h e a v y c r e a m (37.0 to 43.5 p e r c e n t f a t ) i n d i c a t e d t h a t t h e t o t a l solids r e s u l t s a g r e e d m o r e s a t i s f a c t o r i l y w i t h those o b t a i n e d w i t h t h e " O f f i c i a l M e t h o d " w h e n a t w o - g r a m s a m p l e was d r i e d i n t h e D i e t e r t a p p a r a t u s a t 120 ° C. f o r 25 m i n u t e s Using a 75-mm. dish. C o n s e q u e n t l y , this p r o c e d u r e is r e c o m m e n d e d f o r all c r e a m samples. T a b l e 3 i l l u s t r a t e s t h e e x p e r i e t l c e w i t h f o u r s a m p l e s of l i g h t c r e a m t e s t e d b y t h e D i e t e r t a n d M o j o n n i e r M e t h o d s a n d t a b l e 4 pres en t s s i m i l a r d a t a c o v e r i n g five s a m p l e s o f - h e a v y cream. T h e t o t a l solids r e s u l t s o b t a i n e d w i t h t h e D i e t e r t M e t h o d a r e j u s t as a c c u r a t e , o n - t h e whole, as w i t h t h e M o j o n n i e r f o r l i g h t a n d h e a v y cream. TABLE 4 Accuracy of the selected Dietert procedure for determining total solids of heavy cream as judged by the results obtained with the "Official Method" and as compared with those found by the Mojonnier method Per cent T.S. ' ' Official ' ' 41.63 46.94 43.06 42.3] 47.80
Results with Dietert apparatus
Results with iVfojonnier tester
Per cent T.S.
Per cent T.S.
42.13 41.96 41.60 47.10 47.02 47.02 43.08 43.04 43.02 42.39 42.37 42.32 47.92 47.82 47.79
Variation from ' ' Official ' ' + 0.50 + 0.33 - 0.03 + 0.16 + 0.08 + 0.08 +0.02 - 0.02 - 0.04 + 0.08 +O.06 + 0.01 + 0.12 + 0.02 O.01 -
Algebraic average .................................... + 0.091 Arithmetical average ......................... + 0.104 Range ................................................................... -0.04 to + 0.50
41.63 41.83 41.75 47.16 47.19 47.08 43.27 43.19 43.31 42.46 42.46 42.41 48.05 47.95 47.91
Variation from c, Official ' ' 0.00 + 0.20 + 0.12 + 0.22 + 0.25. + 0.14 +0.21 +0.13 + 0.25 +0.15 + 0.15 +0.10 + 0.25 +0.15 +0.Ii
+ 0.162 + 0.162 0.00 to + 0.25
Condensed M il k , C o n d e n s e d S k i m M i l k and E v a p o r a t e d M i l k I n a s m u c h as t h e r e s u l t s o b t a i n e d w i t h m i l k a n d c r e a m i n d i c a t e d t h a t temp e r a t u r e s u n d e r 120 ° C. w e r e u n s a t i s f a c t o r y f o r d r y i n g w i t h t h e D i e t e r t a p p a r a t u s a n d since c o n c e n t r a t e d m i l k s a r e k n o w n to d r y less r e a d i l y , t h e study" of v a r i a b l e s was l i m i t e d to t e m p e r a t u r e s of 120 ° C. a n d a b o v e w i t h t h es e p r o d u c t s . T h e " O f f i c i a l M e t h o d " used w as t h a t r e c o m m e n d e d f o r e v a p o r a t e d m i l k a n d D i e t e r t s a m p l e s c o n s i s t ed of (a) one g r a m of t h e p r o d u c t p l u s one ml. of w a t e r , (b) t w o g r a m s of the p r o d u c t a n d (c) t w o g r a m s of t h e p r o d u c t d i l u t e d as p r e s c r i b e d i n ' ' Official M e t h o d s . " T h e r e s u l t s i n d i c a t e d t h a t all these p r o d u c t s r e s p o n d e d best to t h e s a m e c o n d i t i o n s of d r y i n g . T h e r e c o m m e n d e d p r o c e d u r e is to d r y one g r a m of t h e p r o d u c t d i l u t e d w i t h
718
C. w .
L I V A K AND F. J . TABLE
DOAN
5
Accuracy of the selected Dietert procedure for determining total solids of condensed milk, condensed s~im mil~ and evaporated milk as judged by the results obtained with the "Official M e t h o d " (evaporated milk) and as compared with those f o u n d by the Mojonnier method Per cent T.S. c, Official ' '
Results with Dietert apparatus Per cent T.S.
Variation from ~Official ' '
Per cent T.S. ' ~Official ' '
Results with Mojonnier tester Per cent T.S.
Variation from ~' Official ' '
Condensed milk 45.12
45.24 45.30
+ 0.12 + 0.18
36.06
43.22
43.31 43.14
+0.09 - 0.08
44.76
45.12
45.16 45.26
+ 0.04 + 0.14
43.22
A l g e b r a i c a v e r a g e ............. A r i t h m e t i c a l a v e r a g e ...... R a n g e .....................................
+ 0.095 + 0.108 - 0.08 t o + 0.18 Condensed
28.91
28.30
28.30
27.93
36.18 36.39 36.07 44.90 44.95 44.59 43.39 43.52
40.12 + 0.33 + 0.01 + 0.14 + 0.19 -0.17 40.17 + 0.30 + 0.157 + 0.179 - 0.17 t o + 0.30
kim milk 28.66 28.71 28.84 27.14 27.08 27.14
+ 0.08 40.13 + 0.26 + 0.05
29.04 28.93 29.03 28.55 28.41 28.07 28.51 28.53 28.50
+ 0.13 - 0.02 + 0.12 + 0.25 + 0.11 - 0.23 + 0.21 +0.23 +0.20
28.58
27.07
27.26 27.19
+ 0.05 40.19 + 0.12
27.67 27.78 27.85
-0.26 - 0.15 - 0.08
27.74
27.98 27.85 27.81
+ 0.24 +0.11 +0.07
27.09
A l g e b r a i c a v e r a g e .............. + 0 . 1 0 4 A r i t h m e t i c a l a v e r a g e .... +_ 0 . 1 6 6 R a n g e ............................................. - 0.26 t o + 0.25
-
0.01
+ 0.118 _+0 . 1 1 9 - 0.01 t o + 0.26
Evaporated milk 26.18
26.05
26.00
26.14
26.09
26.22 26.16 26.10 26.03 26.05 26.12
+ -
0.04 0.02 0.08 0.02 0.00 + 0.07
26.18
26.01 26.03 26.00 26.13 26.08 26.08 26.08 26.15 26.12
+ 0.01 + 0.03 0.00 -0.01 -0.06 - 0.06 - 0.01 + 0.06 +0.03
26.00
A l g e b r a i c a v e r a g e ............... - 0.017 A r i t h m e t i c a l a v e r a g e ...... _+ 0.033 R a n g e ............................................ - 0.08 t o + 0.07
26.05
26.14
26.09
26.11 26.14 26.18 26.14 26.13 26.17 26.09 26.18 26.08 26.09 26.07 26.05 26.07 26.04 26.07
-0.07 -0.04 0.00 + 0.09 + 0.08 40.12 + 0.09 40.18 + 0.08 - 0.05 - 0.07 - 0.09 -0.02 -0.05 - 0.02 + 0.037 + 0.064 - 0.09 to + 0.12
719
DETERMINATION OP TOTAL SOLIDS
one ml. of water, for 25 minutes at 120 ° C. Results obtained with several samples of each of the three products are shown in table 5. I t is obvious from these data that the Dietert procedure for determining total solids in concentrated fluid dairy products gives results which are just as accurate as those obtainable with the Mojonnier tester and in reasonably good agreement with "Official Methods."
Effect of Clogging of Screen of Dishholder The dishholder of the Dietert apparatus has a fine woven screen bottom through which the moisture-laden, hot air leaves the assembly. At one stage in the analytical work it was noted that total solids results were abnormally high and tended to become higher in additional trials. Examination revealed TABLE
6,
Effect of clogging of the screen of the dishholder of the Dietert apparatus on analytical results
Product analyzed Condensed skim milk Fluid milk Condensed whole m i l k S w e e t e n e d condensed whole milk
Condition of dishholder Dirty Clean Dirty Clean Dirty Clean Dirty Clean
A v e r a g e a l g e b r a i c pe r c e n t v a r i a t i o n i n t o t a l s ol i ds f r o m ~' Official ' ' w he n d r i e d a t II0 °
C.
+ 3.25 + 0.30 +4.22 + 0.39
120 ° C.
130 ° C.
+ + + + +
+ + + +
-
1.40 0.05 1.39 0.07 0.74 0.14
1.04 0.32 0.43 0.02 0.41
140 ° C.
150 ° C.
+ 0.54 0.82 +0.14 -
-
0 . 1 6
+ 1.48 0.03 -
that the dishholder screens had become clogged with what appeared to be fine carbon from the motor brushes. When this was discovered a comparison of results obtained on several products using the d i r t y dishholders and new unused dishholders was made. A portion of these are included in table 6. These data indicate that the clogged screens caused a diminution of the amount of air passing through the apparatus, restricting evaporation and resulting in incomplete drying of the samples. It was f o u n d necessary to clean the dishholders frequently and thoroughly. Their condition can readily be ascertained by viewing them before a strong light. CONCLUSIONS
Evidence has been presented showing that t h e " Dietert Moisture T e l l e r , " a drying apparatus employing forced, heated air, can be used conveniently in the determination of total solids in fluid whole milk, fluid skim milk, light and heavy cream, condensed whole milk, condensed skim milk and evaporated milk.
720
c.w.
LIVAK AND F. J. DOAN
R e s u l t s h a v i n g as h i g h a d e g r e e of a c c u r a c y as t h e M o j o n n i e r t e s t e r a r e o b t a i n a b l e w i t h t h e D i e t e r t a p p a r a t u s w h e n fluid m i l k s a m p l e s a r e d r i e d a t 120 ° C. f o r 20 m i n u t e s a n d w h e n c r e a m a n d t h e a f o r e - m e n t i o n e d concent r a t e d m i l k p r o d u c t s a r e d r i e d a t t h e same t e m p e r a t u r e f o r 25 m i n u t e s . A s i n g l e s o l i d s d e t e r m i n a t i o n c a n be c o m p l e t e d w i t h i n one h o u r w i t h t h e " D i e t e r t 1V[oisture T e l l e r . " W i t h t h e M o j o n n i e r t e s t e r this w i l l r e q u i r e a b o u t 35 m i n u t e s p r o v i d e d t h e oven a n d p l a t e a r e a t t h e r e q u i r e d t e m p e r a t u r e , otherwise, s o m e w h a t m o r e t h a n one h o u r w i l l be needed. A d e t e r m i n a t i o n b y " O f f i c i a l M e t h o d s " will t a k e f r o m t h r e e to f o u r hours, d e p e n d i n g on t h e p r o d u c t a n d on t h e a l t e r n a t i v e m e t h o d selected. REFERENCES (1) I-IALVORSON,It. A. Report on the Determination of Moisture in Food Stuffs and Agricultural Products. Jour. Assn. Off. Agr. Chem., 20: 435-438. 1937. (2) Official and Tentative Methods of Analysis of the Association of Official Agricultural Chemists, 5th Ed. 1940. (3) MOZONNIER,T., AND TROY, H.C. The Technical Control of Dairy Products. Published by Mojonnier Bros. Co., Chicago, Ill., 2nd Ed. 1925. (4) MONROE, C. F., AND PERKINS, A . E .
A Rapid Method for Determining Moisture in
Roughages. Joua. DAIRY ScI., 22: 37-39. 1939. (5) MURI)OCK, F. R. Grass and Legume Silages, Their Methods of Preservation and Nutritive Values with Special Reference to Carotene. Dissertation, The Pennsylvania State College, 1943.
LIVAK
A~D
F. ft. DOAN
The Pennsylvania Agricultural J~xpe~'iment S~atio~, State College, Pa.
It is generally conceded that moisture determinations in biological materials must follow empirical procedures and this viewpoint is confirmed by Halvorson (1), who in 1937 published a thorough survey of methods recognized by the Association of Official Agricultural Chemists. He concluded that it is not possible to arrive at the absolute water content of agricultural products and that the only practical method of determining total solids or moisture is to define them in terms of the residue or loss resulting from drying the materials u n d e r definitely specified conditions of temperature, time, pressure and any other factors which influence the rate or degree of moisture loss. The Mojonnier methods (3) based on A.O.A.C. definitions (2) of total solids are generally accepted as satisfactory by the dairy industry. Not all laboratories can justify the cost of Mojonnier testers, however, and are forced to use the slower "Official Methods" or the less accurate indirect methods employing hydrometers. Moreover, in cases where only one or two samples are to be analyzed the Mojonnier tests can h a r d l y be called convenient inasnmch as considerable time is required for bringing the hot plates to the required temperatures. Thus, there is a need for a quick, accurate and inexpensive method for determining the total solids in dairy products, especially where only one or two samples are analyzed at one time. An instrument known as the " D i e t e r t Moisture T e l l e r , " originally designed for determining the moisture content of sand, coke, gravel, cinders, etc., has been f o u n d satisfactory for agricultural roughages (4, 5) and appeared to offer possibilities for the estimation of total solids in fluid dairy products. Consequently, its use for this purpose was subjected to detailed study and the results constitute the basis for this report. T H E ~' DIETERT :MOISTUI~E T E L h E R ' ' AND ITS USE
Briefly, the " D i e t e r t Moisture Teller," illustrated in figure 1, consists of an electric blower and heating element encased in the u p p e r portion of a tube which Germinates at the bottom in a flared enlargement. A removable pan (dishholder), the bottom of which is constructed of fine woven brass l~eceived f o r p u b l i c a t i o n A p r i l 16, 1945. A u t h o r i z e d f o r p u b l i c a t i o n on A p r i l 10, 1945, as p a p e r no. 1279 in the J o u r n a l Series of t h e P e n n s y l v a n i a A g r i c u l t u r a l E x p e r i m e n t S t a t i o n . 7]]
712
C.W.
LIVAK AND F. J. DOAN
screening, is held snugly against the flared end of the tube by means of a spring clamp. The tube contains an air diffuser and a thermometer located immediately over the pan. At the top of the upright panel, to which the mechanism is attached, an automatic timing dial and switch are placed. The dial is graduated in half-minute intervals from zero to 15. Thirty- and 60-minute timers are also available. A thermo-regulator is attached to the flared base of the tube at the right side and just above the pan. Temperature adjustments are made by merely turning a knurled knob.
Fro. 1. The Dietert Moisture Teller: A, dishholder; B, interval timer and switch; C, thermo-regulator; D, total solids dish. The instrument is manufactured by the H. W. Dietert Company, 9330 Roselawn Avenue, Detroit, Michigan.
In using the Dietert apparatus for drying samples of fluid dairy products for the purpose of determining the total solids, suitable sample dishes (Mojonnier solids dishes are satisfactory), a laboratory desiccator of proper size, and an analyticM balance are required. All precautions in the weighing of samples'and residues and in the handling and cooling of dishes, etc., customarily required in quantitative analysis must be observed. Preliminary adjustments of the thermo-regulator should be made. The
DETERMINATION
OIP T O T A L SOLIDS
713
apparatus is then turned on by moving the timing pointer past three on the dial. This starts the blower and sends current through the heating elements. When the thermometer shows that the air temperature has reached the desired point, the pan containing the centered dish (tared) and well-spread sample is inserted in the clamp ring. Then the timer is set for the interval of drying desired. The draft of heated air is directed evenly onto the sample, rapidly evaporating the moisture and carrying it out through the screen base of the pan or dishholder. When the set time has elapsed the blower and heat are automatically cut off. At this point the dish containing the dried residue from the sample should be promptly removed to a desiccator and allowed to cool to balance temperature for accurate subsequent weighing. METHODS AND PROCEDURE
Preliminary observations revealed that the " D i e t e r t ~oisture Teller" was capable of rapidly removing moisture from dairy products and producing an apparently dry residue. Three different units when operated at the same temperatures and time intervals gave closely agreeing weights of residues from various fluid dairy products when all variables were controlled. Efforts to use comparatively large samples and less expensive balances of the torsion type failed to give consistent results and it was found necessary to use an analytical balance with careful adherence to recognized analytical practices in weighing the dishes, samples and residues. The possibility of using smaller sample dishes and drying duplicate or triplicate samples in the apparatus simultaneously was thoroughly investigated but erratic results were obtained. This, however, does not preclude the pro.bability that satisfactory multiple drying units can be constructed uulizing the principle of forced, heated air. After preliminary work had shown the capabilities of the Dietert apparatus and had narrowed down the number of the variables, some of which are mentioned above, it was deemed necessary to study each product separately in order to determine the most suitable time and temperature of drying, the best quantity of sample, whether dilution of the sample is advantageous, the proper diameter of dish, etc. To do {his, a large number of determinations were made, varying one factor at a time and comparing results with the average o~ triplicate determinations made according to "Official Methods." Scrupulous care was exercised in all of the work to avoid any fortuitous influences and to assure that the results represented only the effect of the variable under consideration. Seven samples of milk varying in fat content from 3.7 per cent to 4.4 per cent were analyzed for total solids in triplicate using the method given in the Fifth Edition of "Official and Tentative !V~ethods of Analysis" (2) including the use of sand (optional) and an aluminum dish 75 ram. in diameter. These samples were then analyzed in triplicate by means of the " D i e t e r t
714
C. W .
L I V A K AND F. J .
DOAN
Moisture Teller," using 16 different combinations of drying intervals (10 to 25 minutes) and temperatures (100 ° to 125 ° C.) and employing both oneand two-gram gamples. The results were compared with the average of those obtained by the "Official Method." After a suitable temperature and drying interval had been selected for use with the Dietert apparatus three additional samples of milk were analyzed using triplicate dishes having diameters of 50, 65, 75, 90, 95 and 100 ram., respectively. Substantially the same method was utilized for verifying a satisfactory Dietert procedure for determining the total solids of fluid skim milk, light and heavy cream and plain condensed whole and skim milk using between 6 and 12 samples for each product and omitting the 100 ° C. temperature. In the case of the concentrated products the Dietert samples consisted of (a) one gram of product plus one ml. of water, (b) two grams of product and (c) two grams of the product diluted as required in "Official Methods" for evaporated milk. Following the establishment of what was considered a suitable Dietert procedure a limited number of samples of each of the products were analyzed in triplicate using this procedure and the results compared with the average of triplicate determinations made b y " Official Methods." For comparative purposes they were also analyzed in triplicate by the Mojonnier Method. The preliminary study using dishes of different diameters indicated that the 75-mm. dish gave more satisfactory results with most of the products and at least as satisfactory with all products than dishes of any other size. RESULTS
Milk Observations made oll the drying of milk samples with the Dietert Moisture Teller indicated that fairly satisfactory total solids results could be obtained with either a one-gram or a two-gram sample and at high temperatures for shorter drying periods or at low temperatures for longer intervals. Analysis revealed, however, that while average results might be similar, the larger sample and longer drying intervals gave more uniform and closely agreeing results. On the basis of this study the following procedure was deemed the most satisfactory of those tried and is suggested for use with the " Dieter t Moisture Teller." Procedure for milk. A flat-bottom dish of 75 ram. diameter is heated in the Dietert apparatus for at least 10 minutes during which time the temperature of the apparatus is checked and adjusted. It is cooled in a desiccator to balance temperature and weighed, with a suitable cover, using an analytical balance. Approximately two grams of well-mixed milk are then put into the dish and accurately and quickly weighed (weighing pipettes may be used). The milk is spread evenly over the dish and it is placed in
DETERMINATION
OF
TOTAL
715
SOLIDS
t h e c e n t e r of t h e p a n of t h e o p e r a t i n g D i e t e r t a p p a r a t u s i n a l ev el position. T h e t e m p e r a t u r e s h o u l d a g a i n be c h e c k e d a n d d r y i n g s h o u l d be c a r r i e d o u t f o r 20 m i n u t e s at 120 ° C. W h e n d r y i n g is c o m p l e t e d , t h e dish s h o u l d be i m m e d i a t e l y t r a n s f e r r e d to a l a b o r a t o r y d e s i c c a t o r u n t i l cool. I t is t h e n weighed, w i t h cover, a n d t h e w e i g h t of d r y r e s i d u e e x p r e s s e d as p e r c e n t of t o t a l solids. Confirmation of accuracy. T o t a l solids w e r e d e t e r m i n e d in t r i p l i c a t e in five s a m p l e s of m i l k u s i n g the a b o v e p r o c e d u r e a n d also t h e M o j o n n i e r M et h o d . T h e r e s u l t s w e r e c o m p a r e d w i t h t h e a v e r a g e r e s u l t s of t r i p l i c a t e TABLE 1 Accuracy of the selected Dietert procedure for determining total solids of fluid whole milk as judged by the results obtained with the "Official M e t h o d " and as compared with those found by the Mojonnier method Per cent T.S. ' ' Official ' ' 12.32 12.69 12.75 12.80 12.75
Results with Dietert apparatus Per cent T.S. 12.38 12.44 12.34 12.82 12.84 12.77 12.77 12.74 12.71 12.80 12.75 12.78 12.84 12.83 12.77
Variation from ' ' Official ' '
-
................................................ - 0.05
Per cent T.S. 12.38 12.35 12.36 12.73 12.76 12.71 12.87 12.87 12.91 12.76 12.81 12.79 12.77 12.71 12.67
+0.06 +0.12 + 0.02 +0.13 +0.15 +0.08 + 0.02 0.01 - 0.04 0.00 - 0.05 - 0.02 + O.O9 + 0.08 +O.02
Algebraic average ...................................... + 0.043 Arithmetical average ............................ _+0.059 Range
Results with/¢Iojonnier tester Variation from ' ~Official ' ' + 0.06 + 0.03 +0.04 + 0.04 + 0~07 + 0.02 + 0.12 + 0.12 + 0.16 -
ft.04
+ 0.01 -0.01 +0.02 - 0.04 -0.08 + 0.036 +_0.057
to
+ 0.15
- 0.08
to + 0.16
d e t e r m i n a t i o n s b y the " O f f i c i a l M e t h o d . " T h e c o m p a r a t i v e d a t a ar e s h o w n i n t ab l e 1. I t a p p e a r s t h a t t h e D i e t e r t a p p a r a t u s is c a p a b l e of g i v i n g t o t a l solids results, w i t h milk, w h i c h closely p a r a l l e l t h e a c c u r a c y of t h e M o j o n n i e r Method. T h i s a c c u r a c y is c o n s i d e r e d h i g h l y s a t i s f a c t o r y . Skim Milk
T h e e x p e r i e n c e w i t h fluid skim m i l k in v a r y i n g t h e t i m e a n d t e m p e r a t u r e of D i e t e r t d r y i n g , the size of s a m p l e a n d size of dish was p r a c t i c a l l y i d e n t i c a l w i t h t h a t of f lu id w h o le milk. C o n s e q u e n t l y , t h e s a m e p r o c e d u r e was sel e c t e d as b e i n g best s u i t e d to this p r o d u c t . T a b l e 2 shows t h e c o m p a r a t i v e a c c u r a c y a t t a i n e d e m p l o y i n g the D i e t e r t a p p a r a t u s a n d t h e M o j o n n i e r t e s t e r w i t h five s a m p l e s of fluid skim milk.
716
c.w.
L I V A K AND F. J . TABLE
DOAN
2
Accuracy of the selected Dietert procedure for determining total solids of fluid skim qnil~ as j u d g e d by the results obtained w i t h the "Official M e t h o d " and as compared with those fo~nd by the Mojo~nier method Per cent
Results with Dietert apparatus
T.S. ' ' Official ~~
Per cent T.S.
9.10
9.13 9.15 9.09 Lost 9.03 9.01 9.19 9.21 9.18 9.27 9.25 9.25 9.19 9.21 9.20
8.96
9.10
9.18
9.14
Results with Mojonnier tester
Varlation from ~' Official ' '
Per cent T.S. 9.16 9.18 9.15 8.98 8.99 8.98 9.13 9.12 9.11 9.24 9.24 9.24 9.10 9.13 9.11
+0.03 + 0.05 0.01 -
+0.07 + 0.05 + 0.09 +0.11 + 0.08 + 0.09 +0.07 + 0.07 + 0.05 + 0.07 +O.06
A l g e b r a i c a v e r a g e ................................... A r i t h m e t i c a l a v e r a g e ....................... R a n g e ....................................
+ 0.063 + 0.064 - 0.01 to + 0.11
Variation from ' ' Official ' ' + 0.06 + 0.08 + 0.05 +0.02 +0.03 + 0.02 +0.03 +0.02 +0.01 + + + -
0.06 O.O6 0.06 0.04 0.01 -0.03 -
+ 0.028 _ 0.039 - 0.04 t o + 0.08
Cream C r e a m s a m p l e s w e r e f o u n d to be s o m e w h a t m o r e difficult to d r y t h a n m i l k a n d s k i m m i l k samples. This was t r u e even of t h e Official m e t h o d . The TABLE
3
Accuracy of the selected Dietert procedure f o r determbning total solids of light cream as j u d g e d by the results obtained with the "Official M e t h o d " and as compared with those f o u n d by the Mojonnier method Per c e n t T.S. ' ' Official ' ' 28.06
25.96
26.08
27.27
Results with Dietert apparatus Per cent T.S. 28.06 28.10 28.03 26.11 25.97 Lost 26.23 26.12 26.05 27.21 27.49 27.18
I
Variation from ' ' Official ' ' 0.00 + 0.04 -0.03 + 0.15 +0.01 +0.15 + 0.04 -0.03 -0.06 + 0.22 - 0.09
A l g e b r a i c a v e r a g e ........................ + 0 . 0 3 6 A r i t h m e t i c a l a v e r a g e ............................. + 0 . 0 7 5 R a n g e ....................................................... - 0.09 t o + 0.22
Results with Mojonnier tester P e r cent
T.S. 28.02 28.05 Lost 26.14 26.08 25.96 26.16 26.16 25.87 27.33 Lost 27.43
V a r i a t i o n from ' ' Official' ' 0.04 -0.01
-
+ o.18 +0.12 0.00
+0.08 +0.08 -0.21 + 0.06 +0.16 + 0.042 _+ 0 . 0 9 4 - 0.21 t o + 0.18
717
DETERMINATION OF TOTAL SOLIDS
s t u d y of v a r i a b l e s w i t h both l i g h t c r e a m (18.0 to 20.5 p e r c e n t f a t ) a n d h e a v y c r e a m (37.0 to 43.5 p e r c e n t f a t ) i n d i c a t e d t h a t t h e t o t a l solids r e s u l t s a g r e e d m o r e s a t i s f a c t o r i l y w i t h those o b t a i n e d w i t h t h e " O f f i c i a l M e t h o d " w h e n a t w o - g r a m s a m p l e was d r i e d i n t h e D i e t e r t a p p a r a t u s a t 120 ° C. f o r 25 m i n u t e s Using a 75-mm. dish. C o n s e q u e n t l y , this p r o c e d u r e is r e c o m m e n d e d f o r all c r e a m samples. T a b l e 3 i l l u s t r a t e s t h e e x p e r i e t l c e w i t h f o u r s a m p l e s of l i g h t c r e a m t e s t e d b y t h e D i e t e r t a n d M o j o n n i e r M e t h o d s a n d t a b l e 4 pres en t s s i m i l a r d a t a c o v e r i n g five s a m p l e s o f - h e a v y cream. T h e t o t a l solids r e s u l t s o b t a i n e d w i t h t h e D i e t e r t M e t h o d a r e j u s t as a c c u r a t e , o n - t h e whole, as w i t h t h e M o j o n n i e r f o r l i g h t a n d h e a v y cream. TABLE 4 Accuracy of the selected Dietert procedure for determining total solids of heavy cream as judged by the results obtained with the "Official Method" and as compared with those found by the Mojonnier method Per cent T.S. ' ' Official ' ' 41.63 46.94 43.06 42.3] 47.80
Results with Dietert apparatus
Results with iVfojonnier tester
Per cent T.S.
Per cent T.S.
42.13 41.96 41.60 47.10 47.02 47.02 43.08 43.04 43.02 42.39 42.37 42.32 47.92 47.82 47.79
Variation from ' ' Official ' ' + 0.50 + 0.33 - 0.03 + 0.16 + 0.08 + 0.08 +0.02 - 0.02 - 0.04 + 0.08 +O.06 + 0.01 + 0.12 + 0.02 O.01 -
Algebraic average .................................... + 0.091 Arithmetical average ......................... + 0.104 Range ................................................................... -0.04 to + 0.50
41.63 41.83 41.75 47.16 47.19 47.08 43.27 43.19 43.31 42.46 42.46 42.41 48.05 47.95 47.91
Variation from c, Official ' ' 0.00 + 0.20 + 0.12 + 0.22 + 0.25. + 0.14 +0.21 +0.13 + 0.25 +0.15 + 0.15 +0.10 + 0.25 +0.15 +0.Ii
+ 0.162 + 0.162 0.00 to + 0.25
Condensed M il k , C o n d e n s e d S k i m M i l k and E v a p o r a t e d M i l k I n a s m u c h as t h e r e s u l t s o b t a i n e d w i t h m i l k a n d c r e a m i n d i c a t e d t h a t temp e r a t u r e s u n d e r 120 ° C. w e r e u n s a t i s f a c t o r y f o r d r y i n g w i t h t h e D i e t e r t a p p a r a t u s a n d since c o n c e n t r a t e d m i l k s a r e k n o w n to d r y less r e a d i l y , t h e study" of v a r i a b l e s was l i m i t e d to t e m p e r a t u r e s of 120 ° C. a n d a b o v e w i t h t h es e p r o d u c t s . T h e " O f f i c i a l M e t h o d " used w as t h a t r e c o m m e n d e d f o r e v a p o r a t e d m i l k a n d D i e t e r t s a m p l e s c o n s i s t ed of (a) one g r a m of t h e p r o d u c t p l u s one ml. of w a t e r , (b) t w o g r a m s of the p r o d u c t a n d (c) t w o g r a m s of t h e p r o d u c t d i l u t e d as p r e s c r i b e d i n ' ' Official M e t h o d s . " T h e r e s u l t s i n d i c a t e d t h a t all these p r o d u c t s r e s p o n d e d best to t h e s a m e c o n d i t i o n s of d r y i n g . T h e r e c o m m e n d e d p r o c e d u r e is to d r y one g r a m of t h e p r o d u c t d i l u t e d w i t h
718
C. w .
L I V A K AND F. J . TABLE
DOAN
5
Accuracy of the selected Dietert procedure for determining total solids of condensed milk, condensed s~im mil~ and evaporated milk as judged by the results obtained with the "Official M e t h o d " (evaporated milk) and as compared with those f o u n d by the Mojonnier method Per cent T.S. c, Official ' '
Results with Dietert apparatus Per cent T.S.
Variation from ~Official ' '
Per cent T.S. ' ~Official ' '
Results with Mojonnier tester Per cent T.S.
Variation from ~' Official ' '
Condensed milk 45.12
45.24 45.30
+ 0.12 + 0.18
36.06
43.22
43.31 43.14
+0.09 - 0.08
44.76
45.12
45.16 45.26
+ 0.04 + 0.14
43.22
A l g e b r a i c a v e r a g e ............. A r i t h m e t i c a l a v e r a g e ...... R a n g e .....................................
+ 0.095 + 0.108 - 0.08 t o + 0.18 Condensed
28.91
28.30
28.30
27.93
36.18 36.39 36.07 44.90 44.95 44.59 43.39 43.52
40.12 + 0.33 + 0.01 + 0.14 + 0.19 -0.17 40.17 + 0.30 + 0.157 + 0.179 - 0.17 t o + 0.30
kim milk 28.66 28.71 28.84 27.14 27.08 27.14
+ 0.08 40.13 + 0.26 + 0.05
29.04 28.93 29.03 28.55 28.41 28.07 28.51 28.53 28.50
+ 0.13 - 0.02 + 0.12 + 0.25 + 0.11 - 0.23 + 0.21 +0.23 +0.20
28.58
27.07
27.26 27.19
+ 0.05 40.19 + 0.12
27.67 27.78 27.85
-0.26 - 0.15 - 0.08
27.74
27.98 27.85 27.81
+ 0.24 +0.11 +0.07
27.09
A l g e b r a i c a v e r a g e .............. + 0 . 1 0 4 A r i t h m e t i c a l a v e r a g e .... +_ 0 . 1 6 6 R a n g e ............................................. - 0.26 t o + 0.25
-
0.01
+ 0.118 _+0 . 1 1 9 - 0.01 t o + 0.26
Evaporated milk 26.18
26.05
26.00
26.14
26.09
26.22 26.16 26.10 26.03 26.05 26.12
+ -
0.04 0.02 0.08 0.02 0.00 + 0.07
26.18
26.01 26.03 26.00 26.13 26.08 26.08 26.08 26.15 26.12
+ 0.01 + 0.03 0.00 -0.01 -0.06 - 0.06 - 0.01 + 0.06 +0.03
26.00
A l g e b r a i c a v e r a g e ............... - 0.017 A r i t h m e t i c a l a v e r a g e ...... _+ 0.033 R a n g e ............................................ - 0.08 t o + 0.07
26.05
26.14
26.09
26.11 26.14 26.18 26.14 26.13 26.17 26.09 26.18 26.08 26.09 26.07 26.05 26.07 26.04 26.07
-0.07 -0.04 0.00 + 0.09 + 0.08 40.12 + 0.09 40.18 + 0.08 - 0.05 - 0.07 - 0.09 -0.02 -0.05 - 0.02 + 0.037 + 0.064 - 0.09 to + 0.12
719
DETERMINATION OP TOTAL SOLIDS
one ml. of water, for 25 minutes at 120 ° C. Results obtained with several samples of each of the three products are shown in table 5. I t is obvious from these data that the Dietert procedure for determining total solids in concentrated fluid dairy products gives results which are just as accurate as those obtainable with the Mojonnier tester and in reasonably good agreement with "Official Methods."
Effect of Clogging of Screen of Dishholder The dishholder of the Dietert apparatus has a fine woven screen bottom through which the moisture-laden, hot air leaves the assembly. At one stage in the analytical work it was noted that total solids results were abnormally high and tended to become higher in additional trials. Examination revealed TABLE
6,
Effect of clogging of the screen of the dishholder of the Dietert apparatus on analytical results
Product analyzed Condensed skim milk Fluid milk Condensed whole m i l k S w e e t e n e d condensed whole milk
Condition of dishholder Dirty Clean Dirty Clean Dirty Clean Dirty Clean
A v e r a g e a l g e b r a i c pe r c e n t v a r i a t i o n i n t o t a l s ol i ds f r o m ~' Official ' ' w he n d r i e d a t II0 °
C.
+ 3.25 + 0.30 +4.22 + 0.39
120 ° C.
130 ° C.
+ + + + +
+ + + +
-
1.40 0.05 1.39 0.07 0.74 0.14
1.04 0.32 0.43 0.02 0.41
140 ° C.
150 ° C.
+ 0.54 0.82 +0.14 -
-
0 . 1 6
+ 1.48 0.03 -
that the dishholder screens had become clogged with what appeared to be fine carbon from the motor brushes. When this was discovered a comparison of results obtained on several products using the d i r t y dishholders and new unused dishholders was made. A portion of these are included in table 6. These data indicate that the clogged screens caused a diminution of the amount of air passing through the apparatus, restricting evaporation and resulting in incomplete drying of the samples. It was f o u n d necessary to clean the dishholders frequently and thoroughly. Their condition can readily be ascertained by viewing them before a strong light. CONCLUSIONS
Evidence has been presented showing that t h e " Dietert Moisture T e l l e r , " a drying apparatus employing forced, heated air, can be used conveniently in the determination of total solids in fluid whole milk, fluid skim milk, light and heavy cream, condensed whole milk, condensed skim milk and evaporated milk.
720
c.w.
LIVAK AND F. J. DOAN
R e s u l t s h a v i n g as h i g h a d e g r e e of a c c u r a c y as t h e M o j o n n i e r t e s t e r a r e o b t a i n a b l e w i t h t h e D i e t e r t a p p a r a t u s w h e n fluid m i l k s a m p l e s a r e d r i e d a t 120 ° C. f o r 20 m i n u t e s a n d w h e n c r e a m a n d t h e a f o r e - m e n t i o n e d concent r a t e d m i l k p r o d u c t s a r e d r i e d a t t h e same t e m p e r a t u r e f o r 25 m i n u t e s . A s i n g l e s o l i d s d e t e r m i n a t i o n c a n be c o m p l e t e d w i t h i n one h o u r w i t h t h e " D i e t e r t 1V[oisture T e l l e r . " W i t h t h e M o j o n n i e r t e s t e r this w i l l r e q u i r e a b o u t 35 m i n u t e s p r o v i d e d t h e oven a n d p l a t e a r e a t t h e r e q u i r e d t e m p e r a t u r e , otherwise, s o m e w h a t m o r e t h a n one h o u r w i l l be needed. A d e t e r m i n a t i o n b y " O f f i c i a l M e t h o d s " will t a k e f r o m t h r e e to f o u r hours, d e p e n d i n g on t h e p r o d u c t a n d on t h e a l t e r n a t i v e m e t h o d selected. REFERENCES (1) I-IALVORSON,It. A. Report on the Determination of Moisture in Food Stuffs and Agricultural Products. Jour. Assn. Off. Agr. Chem., 20: 435-438. 1937. (2) Official and Tentative Methods of Analysis of the Association of Official Agricultural Chemists, 5th Ed. 1940. (3) MOZONNIER,T., AND TROY, H.C. The Technical Control of Dairy Products. Published by Mojonnier Bros. Co., Chicago, Ill., 2nd Ed. 1925. (4) MONROE, C. F., AND PERKINS, A . E .
A Rapid Method for Determining Moisture in
Roughages. Joua. DAIRY ScI., 22: 37-39. 1939. (5) MURI)OCK, F. R. Grass and Legume Silages, Their Methods of Preservation and Nutritive Values with Special Reference to Carotene. Dissertation, The Pennsylvania State College, 1943.