Manufacturers of tomato pulp have considerable difficulty in securing
a product of uniform concentration and in determining at what point
to stop evaporation. Some manufacturers turn off the steam when it is
believed that the concentration has gone far enough and make a hasty
determination of specific gravity. If it is found the concentration
is not as great as is desired, heating is resumed for a time and the
specific gravity again determined. Others make but one determination
of specific gravity when it is believed that the desired concentration
has been reached, and if it is found to be underconcentrated, continue
the evaporation for a length of time which experience has indicated to
be necessary. Neither of these methods of operating is satisfactory.
They involve a great deal of work and the concentration of the product
obtained is not sufficiently uniform. Moreover, the determination of
specific gravity of hot pulp is very inaccurate (see p. 44).
A method of employing a gauge stick is believed to be simpler and more
practicable.
Some manufacturers who desire to work with the simplest possible
methods, even at the sacrifice of a high degree of control over the
concentration of their products, measure the volume of cyclone juice
introduced into the evaporating tank; and when it is believed that
the concentration is sufficient, measure the depth of the evaporated
product in the tank, the steam being momentarily turned off for that
purpose and the measurement being taken after the foam subsides. This
method was outlined in detail in a trade paper article published from
this laboratory in 1918. The method is somewhat inaccurate, because
it is based on the measurement of cyclone juice as it flows from the
cyclone and which therefore contains a large amount of air. This air
materially increases the volume of the pulp and consequently the
amount of finished pulp calculated from the volume of cyclone juice
containing this air is greater than can actually be obtained. Some
manufacturers of pulp have found the method practicable, however, by
making a correction based on factory experience on the amount of pulp
which the method indicates should result from the evaporation of each
bath. This method also calls for the use of measuring tanks, which
many manufacturers do not have and do not care to provide. The method
is therefore not repeated here, but the laboratory has a number of
reprints of the trade paper article which are available to any who
desire more detailed information regarding the matter.
The following method has been found more accurate and more convenient
than the one mentioned above. It has the special advantage that it is
based on the examination of the cyclone juice after the juice has been
heated to a sufficient extent to “break” the foam.
In using this method, the manner in which the cyclone juice is prepared
is immaterial. The tomatoes may be broken by steam or mechanical
breaker and may be cycloned hot or cold. The steam may be turned into
the coils as soon as they are covered and the cyclone juice may run
into the evaporating tank until the tank is filled.
Finally, when the last of the cyclone juice is added and the contents
of the tank are boiling vigorously, the steam is momentarily turned
off. The volume is then determined by means of a gauge stick and a
sample is withdrawn, filtered and the specific gravity or degrees Brix
determined as described on page 50. The extent to which evaporation
must be continued to secure pulp of the desired specific gravity is
determined by Table 9.
This table gives in the first four columns the specific gravity of the
partially concentrated pulp taken from the evaporating tank, the per
cent of solids of the same, the specific gravity of the filtrate and
the Brix reading of the filtrate. In order to use the tables, it is
only necessary to make use of one of these columns.
This method of operation can be simplified and more accurate results
obtained by equipping each evaporating tank with a one-inch gage glass
extending the full height of the tank. The gage glass should be open at
the top and connected with the bottom of the tank by a pipe equipped
with a valve. Before the tank is filled with cyclone juice the valve is
turned off and the gage glass filled with water. Steam is turned on as
soon as the pipes are covered and the foam is “broken” quickly without
trouble that was experienced in heating the tank filled with cool pulp.
The heat is continued while the tank is filled to the desired height
with the pulp. The steam is then momentarily turned off and the valve
at the top of the gage glass opened to permit the water in the gage
glass to equalize in height with the partly concentrated pulp within
the tank. The height of water in the gage glass is read by a scale
attached, the sample of the pulp taken for examination and the steam
again turned on.
There is ample time to determine the specific gravity of the sample of
partly concentrated pulp and from its volume as obtained by the gage
glass to calculate the volume to which the pulp should be evaporated
to secure the desired specific gravity in the finished product. The
specific gravity of the sample may be taken by any of the methods
described in the chapter on “Determination of specific gravity.” More
accurate results can be obtained by pouring the sample of pulp as soon
as it is taken into a large loosely stoppered flask and holding the
flask with constant agitation in a tub of ice water until it is brought
to about the temperature of the room.
Having determined the volume (when heated to the boiling point) of a
batch of cyclone juice or of pulp at any stage of its manufacture and
its specific gravity (at 68° F.), each of the last five columns of the
table gives a factor by which the volume of the partially evaporated
pulp may be multiplied to determine the volume of pulp of the specific
gravity given at the top of the column. Since both measurements are
taken at the boiling point the question of temperature need not be
considered.
Table 8.—_Corrections for Specific Gravity and Brix_[19] _Readings at
Different Temperatures to 68 Degrees F._ (_20 Degrees C._)
Corrections to be subtracted from specific gravity or degrees Brix.
===============+=============
Temperature | Corrections
-------+-------+-------+-----
Deg. F.|Deg. C.|Sp. Gr.|Brix.
-------+-------+-------+-----
50 | 10.0 | .0017 | .38
51 | 10.6 | .0016 | .36
52 | 11.1 | .0016 | .35
53 | 11.7 | .0015 | .33
54 | 12.2 | .0014 | .31
| | |
55 | 12.8 | .0014 | .30
56 | 13.3 | .0013 | .28
57 | 13.9 | .0012 | .26
58 | 14.4 | .0011 | .24
| | |
59 | 15.0 | .0010 | .22
60 | 15.6 | .0009 | .20
61 | 16.1 | .0009 | .18
62 | 16.7 | .0008 | .16
63 | 17.2 | .0007 | .13
| | |
64 | 17.8 | .0006 | .11
65 | 18.3 | .0004 | .08
66 | 18.9 | .0003 | .05
67 | 19.4 | .0002 | .03
69 | 20.6 | .0002 | .03
70 | 21.1 | .0003 | .05
71 | 21.7 | .0004 | .08
72 | 22.2 | .0006 | .11
73 | 22.8 | .0007 | .15
| | |
74 | 23.3 | .0009 | .18
75 | 23.9 | .0011 | .21
76 | 24.4 | .0012 | .24
77 | 25.0 | .0013 | .28
78 | 25.6 | .0015 | .32
| | |
79 | 26.1 | .0017 | .35
80 | 26.7 | .0018 | .39
81 | 27.2 | .0019 | .42
82 | 27.8 | .0021 | .46
83 | 28.3 | .0023 | .49
| | |
84 | 28.9 | .0024 | .54
85 | 29.4 | .0026 | .58
86 | 30.0 | .0027 | .62
87 | 30.6 | .0029 | .66
88 | 31.1 | .0031 | .70
-------+-------+-------+-----
[19] These temperature corrections are for a Brix instrument
standardized for 20°C. There are Brix hydrometers on the market
standardized for 17.5°C. Temperature corrections for a Brix hydrometer
standardized at this temperature may be obtained by correcting to
20° by means of the above table (for instrument graduated at 20°C.)
and adding to this corrected reading 0.12. For instance suppose the
reading for a 17.5° instrument is 7.00 at 25°C. The correction from
the above table will be .28 or a total of 7.28. Adding .12 to this
gives a corrected reading of 7.40. If the reading is 7.00 at 15°C.
the correction from the above table amounts to .22 (to be subtracted)
giving 6.78. Adding 0.12 to this gives the corrected reading of 6.90.
TABLE 9.—_Equivalent Volumes of Pulp of Different Degrees of
Concentration_
========================================================================
| | Factor by which to multiply volume of
Tomato pulp | Filtrate | pulp of given specific gravity to
| from pulp | ascertain volume of pulp with
| | equivalent solid content and with
| | specific gravity of
--------+-------+--------+-------+-------+-------+-------+-------+-------
Specific| Per |Specific|Degrees| | | | |
gravity | cent |gravity | Brix | | | | |
at |solids | at | at | 1.030 | 1.035 | 1.040 | 1.045 | 1.050
68° F. | | 68° F.| 68° F.| | | | |
--------+-------+--------+-------+-------+-------+-------+-------+-------
1.0125 | 2.79 | 1.0108 | 2.78 | .384 | .326 | .283 | .249 | .223
1.0130 | 2.92 | 1.0113 | 2.89 | .402 | .342 | .296 | .261 | .234
1.0135 | 3.05 | 1.0118 | 3.02 | .420 | .357 | .310 | .273 | .244
1.0140 | 3.17 | 1.0123 | 3.14 | .437 | .372 | .323 | .285 | .255
1.0145 | 3.30 | 1.0128 | 3.27 | .455 | .388 | .336 | .297 | .265
| | | | | | | |
1.0150 | 3.42 | 1.0133 | 3.40 | .472 | .401 | .348 | .306 | .274
1.0155 | 3.54 | 1.0138 | 3.51 | .489 | .416 | .361 | .318 | .284
1.0160 | 3.67 | 1.0143 | 3.65 | .507 | .431 | .374 | .329 | .294
1.0165 | 3.79 | 1.0148 | 3.77 | .524 | .445 | .387 | .341 | .304
1.0170 | 3.92 | 1.0153 | 3.90 | .542 | .460 | .400 | .352 | .315
| | | | | | | |
1.0175 | 4.05 | 1.0158 | 4.03 | .560 | .476 | .413 | .364 | .325
1.0180 | 4.18 | 1.0163 | 4.15 | .579 | .491 | .426 | .375 | .335
1.0185 | 4.30 | 1.0168 | 4.28 | .596 | .506 | .440 | .387 | .346
1.0190 | 4.43 | 1.0173 | 4.40 | .614 | .521 | .452 | .399 | .356
1.0195 | 4.56 | 1.0178 | 4.53 | .632 | .537 | .466 | .410 | .367
| | | | | | | |
1.0200 | 4.68 | 1.0182 | 4.63 | .649 | .551 | .478 | .421 | .377
1.0205 | 4.81 | 1.0188 | 4.77 | .667 | .566 | .491 | .433 | .387
1.0210 | 4.93 | 1.0192 | 4.87 | .684 | .581 | .504 | .444 | .398
1.0215 | 5.05 | 1.0196 | 4.97 | .701 | .596 | .517 | .456 | .407
1.0220 | 5.17 | 1.0201 | 5.10 | .718 | .610 | .529 | .467 | .417
| | | | | | | |
1.0225 | 5.30 | 1.0206 | 5.22 | .737 | .625 | .543 | .479 | .428
1.0230 | 5.43 | 1.0211 | 5.35 | .755 | .641 | .556 | .490 | .438
1.0235 | 5.55 | 1.0216 | 5.47 | .772 | .656 | .569 | .502 | .448
1.0240 | 5.67 | 1.0220 | 5.57 | .789 | .671 | .582 | .513 | .459
1.0245 | 5.80 | 1.0226 | 5.72 | .808 | .686 | .595 | .525 | .469
| | | | | | | |
1.0250 | 5.92 | 1.0230 | 5.82 | .825 | .701 | .608 | .536 | .479
1.0255 | 6.04 | 1.0235 | 5.94 | .842 | .715 | .620 | .547 | .489
1.0260 | 6.16 | 1.0240 | 6.07 | .859 | .729 | .633 | .558 | .499
1.0265 | 6.28 | 1.0244 | 6.17 | .876 | .744 | .646 | .569 | .509
1.0270 | 6.40 | 1.0249 | 6.29 | .894 | .759 | .658 | .580 | .519
| | | | | | | |
1.0275 | 6.53 | 1.0254 | 6.43 | .912 | .775 | .672 | .592 | .529
1.0280 | 6.65 | 1.0258 | 6.53 | .930 | .789 | .685 | .604 | .539
1.0285 | 6.77 | 1.0263 | 6.65 | .947 | .804 | .697 | .615 | .549
1.0290 | 6.90 | 1.0268 | 6.78 | .965 | .819 | .711 | .626 | .560
1.0295 | 7.02 | 1.0273 | 6.90 | .983 | .834 | .724 | .638 | .570
| | | | | | | |
1.0300 | 7.14 | 1.0278 | 7.03 | 1.000 | .849 | .737 | .649 | .580
1.0305 | 7.26 | 1.0282 | 7.13 | 1.017 | .864 | .749 | .660 | .590
1.0310 | 7.38 | 1.0287 | 7.23 | 1.035 | .878 | .762 | .672 | .600
1.0315 | 7.50 | 1.0292 | 7.35 | 1.052 | .893 | .775 | .683 | .610
1.0320 | 7.63 | 1.0296 | 7.45 | 1.071 | .908 | .788 | .695 | .621
| | | | | | | |
1.0325 | 7.75 | 1.0301 | 7.58 | 1.088 | .924 | .802 | .706 | .631
1.0330 | 7.88 | 1.0306 | 7.70 | 1.107 | .939 | .815 | .718 | .642
1.0335 | 8.00 | 1.0310 | 7.80 | 1.124 | .954 | .828 | .730 | .652
1.0340 | 8.12 | 1.0315 | 7.93 | 1.142 | .970 | .842 | .742 | .663
1.0345 | 8.25 | 1.0320 | 8.05 | 1.160 | .985 | .855 | .753 | .673
| | | | | | | |
1.0350 | 8.37 | 1.0325 | 8.16 | 1.178 | 1.000 | .868 | .765 | .684
1.0355 | 8.50 | 1.0330 | 8.27 | 1.197 | 1.016 | .882 | .777 | .695
1.0360 | 8.62 | 1.0334 | 8.37 | 1.214 | 1.031 | .895 | .788 | .705
1.0365 | 8.74 | 1.0339 | 8.50 | 1.232 | 1.046 | .907 | .800 | .715
1.0370 | 8.86 | 1.0344 | 8.63 | 1.249 | 1.061 | .920 | .811 | .725
| | | | | | | |
1.0375 | 8.98 | 1.0349 | 8.75 | 1.267 | 1.076 | .933 | .823 | .735
1.0380 | 9.10 | 1.0353 | 8.85 | 1.284 | 1.091 | .947 | .834 | .746
1.0385 | 9.23 | 1.0358 | 8.97 | 1.303 | 1.106 | .960 | .846 | .756
1.0390 | 9.35 | 1.0363 | 9.07 | 1.321 | 1.122 | .974 | .858 | .767
1.0395 | 9.48 | 1.0368 | 9.20 | 1.340 | 1.138 | .987 | .870 | .778
| | | | | | | |
1.0400 | 9.60 | 1.0372 | 9.30 | 1.358 | 1.153 | 1.000 | .881 | .788
1.0405 | 9.73 | 1.0378 | 9.45 | 1.377 | 1.168 | 1.014 | .893 | .799
1.0410 | 9.85 | 1.0383 | 9.57 | 1.394 | 1.184 | 1.027 | .905 | .809
1.0415 | 9.97 | 1.0387 | 9.67 | 1.412 | 1.199 | 1.041 | .917 | .820
1.0420 | 10.10 | 1.0393 | 9.80 | 1.431 | 1.215 | 1.054 | .929 | .830
| | | | | | | |
1.0425 | 10.22 | 1.0397 | 9.90 | 1.449 | 1.230 | 1.067 | .941 | .841
1.0430 | 10.35 | 1.0402 | 10.03 | 1.468 | 1.246 | 1.081 | .953 | .851
1.0435 | 10.47 | 1.0406 | 10.13 | 1.486 | 1.261 | 1.094 | .964 | .862
1.0440 | 10.60 | 1.0411 | 10.25 | 1.505 | 1.277 | 1.108 | .976 | .873
1.0445 | 10.72 | 1.0416 | 10.36 | 1.523 | 1.293 | 1.122 | .988 | .884
| | | | | | | |
1.0450 | 10.84 | 1.0420 | 10.45 | 1.540 | 1.308 | 1.135 | 1.000 | .894
1.0455 | 10.96 | 1.0425 | 10.57 | 1.558 | 1.322 | 1.148 | 1.012 | .904
1.0460 | 11.08 | 1.0429 | 10.67 | 1.576 | 1.338 | 1.161 | 1.023 | .915
1.0465 | 11.20 | 1.0435 | 10.83 | 1.594 | 1.353 | 1.174 | 1.035 | .925
1.0470 | 11.33 | 1.0440 | 10.93 | 1.613 | 1.369 | 1.188 | 1.047 | .936
| | | | | | | |
1.0475 | 11.45 | 1.0445 | 11.05 | 1.631 | 1.384 | 1.201 | 1.059 | .946
1.0480 | 11.57 | 1.0449 | 11.15 | 1.649 | 1.400 | 1.215 | 1.071 | .957
1.0485 | 11.70 | 1.0454 | 11.27 | 1.668 | 1.416 | 1.229 | 1.083 | .968
1.0490 | 11.82 | 1.0459 | 11.40 | 1.686 | 1.432 | 1.243 | 1.095 | .979
1.0495 | 11.95 | 1.0465 | 11.53 | 1.705 | 1.449 | 1.256 | 1.107 | .990
| | | | | | | |
1.0500 | 12.07 | 1.0468 | 11.60 | 1.724 | 1.464 | 1.270 | 1.119 | 1.00
1.0505 | 12.20 | 1.0474 | 11.75 | 1.743 | 1.479 | 1.284 | 1.131 | 1.01
1.0510 | 12.32 | 1.0478 | 11.84 | 1.761 | 1.495 | 1.298 | 1.144 | 1.02
1.0515 | 12.45 | 1.0482 | 11.93 | 1.780 | 1.511 | 1.311 | 1.156 | 1.03
1.0520 | 12.57 | 1.0488 | 12.07 | 1.797 | 1.526 | 1.325 | 1.167 | 1.04
| | | | | | | |
1.0525 | 12.69 | 1.0492 | 12.17 | 1.816 | 1.542 | 1.338 | 1.179 | 1.05
1.0530 | 12.81 | 1.0497 | 12.30 | 1.834 | 1.557 | 1.351 | 1.191 | 1.06
1.0535 | 12.93 | 1.0502 | 12.40 | 1.852 | 1.572 | 1.364 | 1.203 | 1.07
1.0540 | 13.05 | 1.0506 | 12.50 | 1.870 | 1.588 | 1.378 | 1.215 | 1.08
1.0545 | 13.18 | 1.0512 | 12.65 | 1.890 | 1.604 | 1.392 | 1.227 | 1.09
| | | | | | | |
1.0550 | 13.30 | 1.0516 | 12.74 | 1.908 | 1.620 | 1.405 | 1.239 | 1.10
1.0555 | 13.42 | 1.0520 | 12.83 | 1.926 | 1.635 | 1.419 | 1.250 | 1.11
1.0560 | 13.55 | 1.0525 | 12.95 | 1.945 | 1.651 | 1.433 | 1.263 | 1.12
1.0565 | 13.67 | 1.0529 | 13.05 | 1.964 | 1.667 | 1.447 | 1.275 | 1.14
1.0570 | 13.80 | 1.0534 | 13.16 | 1.983 | 1.684 | 1.461 | 1.288 | 1.15
--------+-------+--------+-------+-------+-------+-------+-------+-----