Chapter III: Part 3

The apparent specific gravity of the hot pulp is ascertained from the special table prepared for the flask according to the directions given on page 38, and the correction figure for the temperature of the pulp obtained from Table 6 is added. _For example_, this method when applied to a certain sample of hot pulp (without centrifuging) indicated a specific gravity of 0.9874. The temperature of the pulp was found to be 201° F. In Table 6 we find that the correction .0457 is equivalent to 201° F. Adding this to the apparent specific gravity given above, we have 0.9874 × 0.457 or 1.033 which is as nearly as we can determine from the hot pulp the specific gravity that would have been determined by examining the same sample after cooling by method (a). More accurate results can be obtained by working with larger specific gravity flasks. For instance, the specific gravity cup shown in Figure 5 may be made of copper, and may readily be made larger than the glass flasks shown in Figures 1 and 2. All metal flasks will gradually change in weight, owing to the solution of metal by the hot tomato pulp, and their weight should therefore be checked from time to time.

TABLE 6.—_Corrections for Specific Gravity of Hot Pulp_

=========+==========
Temp. °F.|Correction
---------+----------
190 | .0401
191 | .0406
192 | .0411
193 | .0416
|
194 | .0421
195 | .0426
196 | .0431
197 | .0436
|
198 | .0441
199 | .0447
200 | .0452
201 | .0457
|
202 | .0462
203 | .0466
204 | .0472
205 | .0477
|
206 | .0482
207 | .0487
208 | .0492
209 | .0498
|
210 | .0504
211 | .0510
212 | .0515
---------+----------

With a materially larger cup or flask (which should be of metal) a heavier balance and heavier weights should be used than suggested on page 40. In using a specific gravity cup similar to that shown in Figure 5 but holding about 1,000 grams of pulp an assay pulp balance with a capacity of 1,500 can be employed, or owing to the increased accuracy of the larger sample a less accurate and cheaper scale such as the “Howard trip scale,” or better a box scale such as is listed as E. & A. 338, may be employed. In working with a cup of this size a set of weights ranging from 1000 grams to 1 centigram is necessary.

The determination of specific gravity in hot pulp is attended by considerable error. Even if the flask or cup be carried directly to the kettle, and filled as quickly as possible, the pulp is materially cooled in transferring, and by the time the surface is “struck off” sufficient contraction may occur to increase the weight of the contents of the flask and cause material error.

When a pail of hot pulp is carried to another room or building for the determination of specific gravity, the error caused by cooling may be increased. Again, notwithstanding the fact that the pulp is hot, enough air bubbles become incorporated into it in pouring into the cup to make a considerable difference in the weight. These two errors counter balance each other to some extent, but it is impossible to control the manipulation with sufficient uniformity to secure satisfactory results.

The figures obtained in the second column of Table 7 (under the heading “Pouring at boiling temperature”) show the error of this method with carefully calibrated apparatus and working under the best conditions. By comparison with the first column, it will be noted that the results are always low, and that the difference between individual determinations is so great that a correction factor cannot be established. It should be borne in mind that these results were obtained by chemists. When the method is employed even by careful operators in the plant, still greater discrepancies may be expected.

TABLE 7.—_Comparison of Different Methods of Determining Specific Gravity_[18]

=====================================================================
|Specific gravity by different methods of filling cup or flask.
Sample+---------------+---------------+---------------+--------------
Number| Centrifuging | Pouring cold | Pouring at | Dipping at
| at 68°F. | and whirling | boiling | boiling
| | by hand | temperature | temperature
------+---------------+---------------+---------------+--------------
1477 | 1.0610 | | 1.0464 |
Do | 1.0610 | | 1.0449 |
Do | | | 1.0600 |
1484 | 1.0423 | 1.0330 | 1.0380 |
1485 | 1.0347 | | 1.0336 |
1483 | 1.0464 | 1.0437 | 1.042 |
Do | | 1.0420 | 1.0446 |
Do | | 1.0430 | |
Do | | 1.0442 | |
1482 | 1.0441 | 1.0416 | 1.0360 |
Do | 1.0444 | 1.0419 | 1.0410 |
Do | 1.0447 | 1.0424 | 1.0413 |
1481 | 1.0449 | 1.0410 | 1.040 |
Do | 1.0449 | 1.0410 | 1.041 |
Do | | 1.0418 | 1.0397 |
1480 | | 1.0430 | 1.036 |
Do | | 1.0420 | 1.040 |
Do | | 1.0429 | 1.044 |
Do | | | 1.0407 |
1496 | 1.0340 | 1.0330 | |
Do | 1.0341 | 1.0326 | |
Do | | 1.0326 | |
Do | | 1.0346 | | 1.0299
Do | | 1.0341 | | 1.0303
Do | | 1.0341 | | 1.0343
Do | | | | 1.033
1515 | 1.0351 | | | 1.036
Do | 1.0352 | | | 1.035
1519 | 1.0380 | | | 1.0377
Do | | | | 1.0383
Do | | | | 1.0329
Do | | | | 1.0350
1521 | 1.0440 | | 1.0410 | 1.0439
Do | | | 1.0439 | 1.0448
1522 | 1.0500 | | 1.0428 | 1.0493
Do | | | 1.0455 | 1.0508
1524 | 1.0519 | | | 1.0504
1524 | | | | 1.0529
Do | | | | 1.0510
1526 | 1.0519 | | 1.0472 | 1.0529
Do | | | 1.0463 | 1.0525
1528 | 1.0519 | | 1.0509 | 1.0514
Do | | | 1.0485 | 1.0514
1530 | 1.0252 | | 1.0281 | 1.0260
Do | | | | 1.0264
Do | | | | 1.0269
1531 | 1.0291 | | 1.0312 | 1.0294
Do | | | | 1.0311
Do | | | | 1.0313
------+---------------+---------------+---------------+--------------

[18] Table 7 gives the results obtained in the determination of specific gravity of several samples of pulp by different methods. The specific gravity given in the first column under the head “Centrifuging at 68° F.” has been proved to be correct by other analytical methods. It will be noted that where duplicate determinations are given in this column they agree with each other very closely. The errors in the other methods in determining specific gravity are shown in the remaining columns. It will be noted that the duplicates given in these columns vary materially from each other.

It should be stated that the results given under the heading “Pouring cold and whirling by hand” were obtained by much more careful work than is practicable in the factory. The flasks in which the determination was made were equipped with a bail, as shown in Fig. 5. page 44, and the samples were whirled by hand until air bubbles were eliminated as far as practicable by that method. The results, in this column are therefore much more accurate than are obtained by the method as ordinarily practiced.

It was thought that better results might be secured by modifying the construction of a cup in such a manner as to permit it to be filled by dipping below the surface of the pulp in the kettle. A bail made of 3/16-inch wire was, therefore, soldered to the opposite side of the cup (see Fig. 5). By means of the bail the cup was lowered into the kettle. After it was filled with the pulp the attempt was made to remove air bubbles by repeatedly giving the bail a quick twist or circular motion with a sudden stop. The cup was then brought quickly to the surface of the kettle and “struck off” with a straight edge, the outside of the cup and bail washed quickly with water, dried, and the cup and contents weighed.

In using this method the steam is turned off, and as soon as the foam subsides the cup is sunk well below the surface of the pulp. At this time the heat in various portions of the kettle is of course uniform, by reason of the thorough mixture caused by the vigorous boiling. Owing to the large mass of rather viscous material, and the heat of the kettle itself, the contents of the kettle cool slowly, and even after 10 minutes the temperature does not decrease more than 1° F., except at the very surface of the pulp. As a result of several observations, it was found that a thermometer bulb held 3 inches below the surface of the pulp showed a lowering of temperature of not more than 1° F. in 10 minutes and a lowering of only 0.5° F. in from 5 to 7 minutes.

The bail employed was about 6½ inches wide and 8 inches long. There was some difficulty, owing to the pulp spattering on the hands of the operator because of the air escaping from the cup. This might be diminished by the use of a longer bail, or by wearing suitable gloves. When evaporating tanks are used it will probably be necessary to attach the bail to a stick or support of some kind. In addition to permitting this method of filling, the bail has the additional advantage that the cup full of pulp may be handled for washing and conveying to the balance much more conveniently and with less danger of spilling than with the handle on the side of the cup. Again, the bail does not heat when the cup is filled with hot pulp, and for that reason is easier to handle.

(d) HYDROMETER METHOD

Hydrometers are of little value in determining the specific gravity of tomato pulp. With cold pulp they cannot be used at all. With hot pulp a relatively slender hydrometer comes to rest and readings can be taken with more or less accuracy. The value of the reading is relative to the specific gravity of the pulp and varies with the shape of the hydrometer and with the character of the pulp. It is necessary therefore to obtain the relation between the reading of the hydrometer in the hot pulp and the specific gravity (obtained by an accurate method) of the same pulp cooled without evaporation. In the hands of a careful operator some manufacturers have found hydrometers (used with hot pulp) helpful in making pulp of uniform specific gravity.

The hydrometer gives much more accurate results with the filtrate of pulp. As shown on page 31, there is a direct relation between the specific gravity of tomato pulp and of the liquor obtained by filtering or straining the same, so that when the specific gravity of the latter is known that of the former may be ascertained readily by means of a table. This method is peculiarly applicable to the examination of cyclone juice and light pulp from which the insoluble solids may be removed quickly by straining through a cloth, and it therefore affords the most rapid method that is available to the average factory for determining the specific gravity of cyclone juice.

In Table 8 are given a series of corrections making it possible to use this method at any temperature between 50 and 80° Fahrenheit. The more closely the readings are taken to 68° F. the more accurate the results. Moreover, when it is attempted to strain the insoluble solids from hot pulp or cyclone juice, considerable evaporation occurs, causing concentration of the product and producing an error in the results. When hot pulp is handled, therefore, it must be strained as quickly as possible, and more accurate results may be obtained if the pulp is cooled quickly before straining. This may be done by placing in a large can and stirring vigorously while the can stands in ice water, or shaking under water in a large flask.

There are several forms of hydrometer which may be used for determining the specific gravity of the filtrate. The ordinary specific gravity hydrometer is the most logical form to use, since it gives the specific gravity directly. Unfortunately, specific gravity hydrometers with the particular marking required for this work are not a stock article, and would, therefore, have to be made to order. For this reason they would be difficult to obtain and not easily replaced if broken.

The Brix hydrometer appears to solve the difficulty. This hydrometer has no direct relation to specific gravity, but Brix readings can, of course, be converted to the specific gravity readings by a table arranged in parallel columns. Table 9 gives the specific gravity of tomato pulp and the corresponding Brix reading of the filtrate. The Brix hydrometer gives directly the per cent of sugar in a solution of cane sugar, one degree Brix being equivalent to one per cent sugar at the temperature for which the hydrometer was calibrated. This fact and the ordinary purpose for which the instrument is manufactured are of no interest to us in this connection, however. The Brix hydrometer of the range desired for the examination of cyclone juice and pulp is a stock article and can be secured readily.

The instrument can be used with the same accuracy as the specific gravity hydrometer, and the results obtained by it, after correcting for temperature by Table 8, are converted into terms of specific gravity by means of Table 9. The determination of the specific gravity of pulp by means of the hydrometer reading of the filtrate obtained from the pulp has several advantages over the ordinary method of weighing a measured quantity of the pulp. When applied to pulp manufactured from whole tomatoes, the method is reasonably accurate. It is also very rapid and the equipment required is inexpensive. This method is especially applicable to the examination of pulp manufactured from whole tomatoes. It is less applicable to trimming stock pulp, although even with that product the method will be of value, especially for the examination of cyclone juice for the purpose of controlling concentration. With pulp manufactured from trimming stock, the relation of the specific gravity of the pulp to the specific gravity of the filtrate obtained from it will vary according to the nature of the raw material used and also according to the method of manufacture. It seems probable, therefore, that after a manufacturer has determined this relation as applied to his own product, he may be able to use this method with reasonable accuracy even in connection with trimming stock pulp.

The method is adapted especially to the examination of cold pulp or cyclone juice.

The following apparatus is used in this method:

1 Brix hydrometer, graduated at 20.0° C., with a range of 1–10°, graduated in 1/10°.

1 Cylinder of heavy glass, lipped, height 12 inches, diameter 2 inches.

1 Chemical thermometer, graduated in Fahrenheit system up to 212° F.

Since this apparatus is likely to be broken, it is well for each plant that contemplates using the method to equip itself with at least two of each item mentioned above.

The Brix hydrometer mentioned above is suggested because it is a stock article handled by all dealers in chemical apparatus and can be secured quickly. It has the disadvantage that it is relatively large, and in order to use it the filtrate must be prepared in much larger quantity than would be required by a smaller hydrometer. By placing orders well in advance with dealers in chemical apparatus special hydrometers may be made with a bulb about one-half inch in diameter and with a total length of five or six inches. Such hydrometers could be used with a cylinder as small as one inch in diameter. They would require much less liquor than is necessary for the Brix hydrometer and therefore would enable the analyst to obtain results much more quickly. In securing such hydrometers it would be well to order several at a time, since it would require several weeks to replace any that may be broken.

The details of the method are as follows:

Place a piece of cotton cloth of about the texture of ordinary glass toweling over a clean, dry container 10 or 12 inches in diameter or over a No. 10 can. Pour on the cloth a suitable amount of the pulp or cyclone juice to be examined, pick the cloth up by the corners and squeeze gently to separate the greater part of the insoluble solids. The strained liquid left in the vessel will be more or less turbid, according to the pressure exerted in squeezing. The amount of insoluble material producing this turbidity, however, is not usually sufficient to interfere with the examination of the product by means of a hydrometer. If, however, it is necessary to exert considerable pressure to get the amount of filtrate desired and the turbidity is therefore considerable it will be necessary to pass the liquor through a second filter, which, of course, may be done quickly.

Transfer this strained liquid, which for the sake of convenience we will designate as “filtrate,” to the 2-inch cylinder described above, and lower the Brix hydrometer into it until the hydrometer floats. When the hydrometer, becomes stationary, the reading on the stem is taken. In reading the hydrometer it will be noted that, owing to the meniscus, the liquid immediately at the stem rises one or two divisions above the general surface. The reading at the lowest point of the surface is desired. In reading the stem, therefore, allowance for the meniscus should be made and a reading recorded one or two divisions on the scale below the extreme height of the meniscus on the stem. The reading so obtained is recorded as the Brix hydrometer reading of the filtrate.

After determining the Brix reading of the filtrate from the tomato pulp, the corresponding specific gravity of the pulp may be obtained from Table 9. The result obtained by the method should be corrected to the temperature of 68° F., according to Table 8. If it is desired to use the reading of the filtrate from cyclone juice for the purpose of controlling the evaporation of tomato pulp, suitable directions are given below under “Evaporation to Specific Gravity Desired.”

IMPORTANCE OF ACCURACY IN DETERMINING SPECIFIC GRAVITY

The description of the tables given in the following page is intended for those operators who desire to take the trouble to obtain the specific gravity of raw product. Where, as is often the case, the pulp is sold under definite specifications for specific gravity, the care necessary to make these observations with a considerable degree of accuracy will be found to be an economy.

If a product be shipped that is materially below the specific gravity stipulated, the manufacturer will of course be docked and the loss will be considerable. On the other hand, the specific gravity should not be materially above the specifications. The buyer, who is usually a manufacturer of ketchup, desires the pulp of the specific gravity stipulated, and a higher degree of concentration is therefore not a mark of superiority in pulp intended for that purpose. Moreover, material increase in concentration above the specifications of the purchaser causes considerable loss by reason of reduced volume. For instance, 100 gallons of pulp with a specific gravity of 1.036 are equivalent to 103 gallons of a pulp with a specific gravity of 1.035. Again, 100 gallons of pulp with a specific gravity of 1.040 are equivalent to 114.7 gallons of pulp with a specific gravity of 1.035.

When these figures are considered with reference to the entire output of the season, it is apparent that the determination of the specific gravity of the final product is of considerable importance, and will warrant care and, if necessary, the employment of a man who is competent to do the work accurately.

This is well illustrated by an experience of one of the large pulp makers, who was selling pulp under specification of 1.035 specific gravity. Owing partly to an error in his specific gravity apparatus, he was actually turning out pulp of a specific gravity varying from 1.040 to 1.050. In other words, each 100 cases of pulp he delivered were equivalent to from 115 to 126 cases of pulp of 1.035 specific gravity. While this manufacturer was using the greater part of the pulp himself, he had contracted to sell a considerable amount of it, and all that was supplied before the error was noticed was sold at a loss, whereas after the error was discovered he supplied pulp well above the specifications of the buyer at a substantial profit. Even then his profit was not what it should have been. His output would have been 10 per cent greater than it was if the specific gravity of his product had just complied with his specifications.

Another manufacturer who sold his pulp under the specification of 1.035 specific gravity, received a complaint from one of the largest buyers of pulp in the country that the specific gravity was low. The manufacturer then examined samples, which he had retained in his possession, of the various runs, using the method described on page 41, under the head of “Specific gravity of cold pulp without centrifuging.” Seventeen samples in all were examined, and he obtained an average specific gravity of 1.0276. The purchaser had reported a specific gravity of 1.0315–.0039 higher than that obtained by the maker. The manufacturer then brought duplicate samples to this laboratory and the specific gravity was determined in all of them by the method described on page 34, “After centrifuging to eliminate air bubbles.”

While this work was being done the manufacturer himself desired to check the mechanical centrifuge, and attempted to remove the air bubbles from the same samples by swinging the specific gravity cups by hand. He made a special effort to remove the air bubbles in this way, devoting nearly a day to the examination of the 17 samples. Notwithstanding his unusual care, his average specific gravity was 1.0318, while the centrifuge method gave 1.0328. It will be noted that the specific gravity as determined by the centrifuge method was .0013 higher than that obtained by the purchaser, though the latter used a more accurate method than has ordinarily been employed in this determination. This difference has ordinarily been regarded in the industry as insignificant. It is apparent that it is not negligible, however, when we consider that the difference in yield involved amounts to over 4.5 gallons in 100 gallons of pulp.

It is true that all these results are lower than the specifications for which this particular pulp was sold, but the incident illustrates the importance of an accurate determination of specific gravity.

EVAPORATION TO THE SPECIFIC GRAVITY DESIRED

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 --------+-------+--------+-------+-------+-------+-------+-------+-----

TABLE 10.—_Specific Gravity and Solids of Tomato Pulp_[20]

=========+==========
Specific | Per cent
gravity | solids
at 68° F.|_in vacuo_
|at 70° C.
---------+----------
1.0145 | 3.30
1.0150 | 3.42
1.0155 | 3.55
1.0160 | 3.67
1.0165 | 3.80
|
1.0170 | 3.92
1.0175 | 4.05
1.0180 | 4.18
1.0185 | 4.30
1.0190 | 4.43
|
1.0195 | 4.56
1.0200 | 4.68
1.0205 | 4.81
1.0210 | 4.93
1.0215 | 5.05
|
1.0220 | 5.17
1.0225 | 5.30
1.0230 | 5.43
1.0235 | 5.55
1.0240 | 5.67
|
1.0245 | 5.80
1.0250 | 5.92
1.0255 | 6.04
1.0260 | 6.16
1.0265 | 6.28
|
1.0270 | 6.40
1.0275 | 6.53
1.0280 | 6.65
1.0285 | 6.77
1.0290 | 6.90
|
1.0295 | 7.02
1.0300 | 7.14
1.0305 | 7.26
1.0310 | 7.38
1.0315 | 7.50
|
1.0320 | 7.63
1.0325 | 7.75
1.0330 | 7.88
1.0335 | 8.00
1.0340 | 8.12
|
1.0345 | 8.25
1.0350 | 8.37
1.0355 | 8.50
1.0360 | 8.62
1.0365 | 8.74
|
1.0370 | 8.86
1.0375 | 8.98
1.0380 | 9.10
1.0385 | 9.23
1.0390 | 9.35
|
1.0395 | 9.48
1.0400 | 9.60
1.0405 | 9.73
1.0410 | 9.85
1.0415 | 9.97
|
1.0420 | 10.10
1.0425 | 10.22
1.0430 | 10.35
1.0435 | 10.47
1.0440 | 10.60
|
1.0445 | 10.72
1.0450 | 10.84
1.0455 | 10.96
1.0460 | 11.08
1.0465 | 11.20
|
1.0470 | 11.33
1.0475 | 11.45
1.0480 | 11.57
1.0485 | 11.70
1.0490 | 11.82
|
1.0495 | 11.95
1.0500 | 12.07
1.0505 | 12.20
1.0510 | 12.32
1.0515 | 12.45
|
1.0520 | 12.57
1.0525 | 12.69
1.0530 | 12.81
1.0535 | 12.93
1.0540 | 13.05
|
1.0545 | 13.18
1.0550 | 13.30
1.0555 | 13.42
1.0560 | 13.55
1.0565 | 13.67
|
1.0570 | 13.80
1.0575 | 13.92
1.0580 | 14.05
1.0585 | 14.17
1.0590 | 14.29
|
1.0595 | 14.42
1.0600 | 14.54
1.0605 | 14.67
1.0610 | 14.79
1.0620 | 15.03
|
1.0630 | 15.27
1.0640 | 15.52
1.0650 | 15.77
1.0660 | 16.02
1.0670 | 16.27
|
1.0680 | 16.52
1.0690 | 16.77
1.0700 | 17.02
1.0710 | 17.27
1.0720 | 17.51
|
1.0730 | 17.76
1.0740 | 18.00
1.0750 | 18.25
1.0760 | 18.50
1.0770 | 18.75
|
1.0780 | 18.99
1.0790 | 19.24
1.0800 | 19.48
1.0810 | 19.72
1.0820 | 19.97
|
1.0830 | 20.22
1.0840 | 20.47
1.0850 | 20.72
1.0860 | 20.96
1.0870 | 21.21
|
1.0880 | 21.46
1.0890 | 21.70
1.0900 | 21.95
1.0910 | 22.20
1.0920 | 22.45
|
1.0930 | 22.70
1.0940 | 22.94
1.0950 | 23.18
1.0960 | 23.43
1.0970 | 23.68
|
1.0980 | 23.93
1.0990 | 24.18
1.1000 | 24.43
1.1010 | 24.67
1.1020 | 24.92
|
1.1030 | 25.18
1.1040 | 25.42
1.1050 | 25.67
1.1060 | 25.91
1.1070 | 26.16
---------+----------
[20] This table gives the per cent of total solids contained by pulp
of different specific gravities varying from unconcentrated pulp as it
comes from the cyclone to the highly concentrated product.

Illustration: Suppose that when the cyclone juice is all added to the tank the contents of which are vigorously boiling so that they are doubtless of uniform composition, the volume is found by the gauge stick to be 815 gallons. A sample of this partially evaporated pulp is withdrawn and filtered and the filtrate is found to have a Brix reading of 6.90. Let us suppose that the product is to be evaporated to a pulp having a specific gravity of 1.035 and the operator desires to know at what point to turn off the steam. By referring to Table 9 in the column headed by the figure 1.035, we find opposite the Brix reading 6.90 the factor .834. Multiplying the volume of the pulp (815 gallons) by this factor, we obtain 680 gallons. It follows, therefore, that the steam should be turned off when the evaporation has reached such a point that the gauge stick shows the volume of pulp to be 680 gallons.

Table 9 may be used in the same way for calculating the volume of any pulp, hot or cold, of any specified specific gravity equivalent to a certain volume of pulp of any other stated specific gravity when held at the same temperature. For instance, the illustration given above serves equally well to illustrate how the relative value of two finished pulps of different specific gravities may be calculated. It also shows directly the relative value (based on tomato solids alone) of the same volume of two pulps of different gravity.

Illustration: Suppose a shipment contains 1,000 cases of No. 10 cans of pulp thought to have a specific gravity of 1.040 but found on examination to have a specific gravity of 1.0365. What is the value of the pulp in comparison with pulp of specific gravity of 1.040? Turning in Table 9 to the figure 1.0365 in the left-hand column we follow the horizontal line containing that figure to the column headed by specific gravity 1.040. Here we find that .907 is the factor by which to multiply the volume of pulp of a specific gravity 1.0365 to obtain the equivalent volume of pulp of specific gravity 1.040. The answer to our question therefore is 1000 × .907 = 907. In other words pulp of a gravity of 1.0365 judged by the tomato solids it contains, has 90.7 per cent of the value of pulp of the gravity of 1.040.

Table 9 is based on the results obtained from a series of samples of whole tomato pulp and cyclone juice varying in specific gravity from 1.02 to 1.05. The table was extended by calculation to give corresponding values for more dilute cyclone juices and more concentrated products. The lower portion of the table has been repeatedly confirmed by results obtained in the examination of cyclone juice and pulp, but the figures in the higher portion of the table are based on calculation from lower concentrations.

This table is only applicable to pulp to which no other substance, such as salt, has been added. Salt if present to the extent of more than 0.25 per cent can be recognized by the taste. The amount of salt, when any has been added, may be determined by the method given on page 33 and the specific gravity corrected by subtracting from the apparent specific gravity 0.007 for each per cent of salt present. This gives the specific gravity of the salt-free pulp and the corresponding per cent of solids may be obtained from Table 9.

TOMATO KETCHUP

Ketchup is defined in the Federal food standards as the clean, sound product made from properly prepared pulp of clean, sound, fresh, ripe tomatoes, with spices, and with or without sugar and vinegar.

The solid matter, or total solids, in ketchup varies from less than 12 per cent to over 37 per cent. This means that the product varies from a substance having barely sufficient tomato added to give color and taste, to a rich, heavy tomato ketchup. The variation of total solids in any one brand is, of course, less, but large differences are not unusual. Three bottles of one brand showed a solids content varying from 12 per cent to 16 per cent, and seven of another brand varied from 32 per cent to 37.2 per cent.

The amount of solids in a non-preservative ketchup should be not materially less than 28 per cent. It is necessary to have a rather high solid content for ketchup of this kind, so that it may keep after being opened on the consumer’s table.

The variation in the insoluble solids is comparable to that in the total solids. The values for a number of samples examined in this laboratory ranged from .9 per cent to 2.3 per cent. As the insoluble solids come from the tomato pulp the amount of insoluble solids is to that extent an indication of the amount of tomato pulp used in the manufacture of the ketchup from whole tomato pulp. The consistency of the ketchup is dependent chiefly on the amount of insoluble tomato solids present.

The ash usually varies from 2 per cent to 4 per cent, owing to the different amounts of salt, which varies in general from 1½ to 3 per cent.

The acidity ranges from .4 to 2.3 per cent. The acidity is one of the most important factors in preventing the growth of bacteria and yeasts in the ketchup after being opened. In order to secure the best results the ketchup should have an acidity of over 1 per cent (expressed as acetic acid) and an acidity of 1.25 per cent or higher adds to the keeping quality of the ketchup after the bottle is opened. An increase in acidity will necessarily require an increase in the amount of sugar in order to secure the proper flavor; or, vice versa, an increase in the sugar will necessitate an increase in acidity. In some ketchups about one-half of the acidity is due to the citric acid of the tomatoes and the remainder to the vinegar added in manufacture. With ketchups of exceptionally high acidity, the proportion of citric acid to total acid may be much less than this. There may be considerable difference in the acidity in ketchup of the same brand due to variations in manufacture.

The sugar present in the ketchup is derived both from the pulp and from the added sugar. In ketchup ranging from 12 to 30 per cent total solids, from 9 to 22 per cent of the solids may consist of sugars.

METHODS OF MANUFACTURE

Ketchup may be prepared either from the fresh tomatoes, or from pulp. The most common practice is to prepare it from fresh tomatoes, although some manufacturers prefer to make ketchup during the winter, when they are not so busy with other products, and therefore use pulp. Presuming that the same quality of stock is used and the same care used in manufacture, there are some advantages in making ketchup from fresh tomatoes. The pulp loses some of its color by bleaching, and a ketchup made from pulp is naturally subjected to more heating than that made from fresh tomatoes.

In the manufacture of ketchup the fresh tomatoes may be broken by steam or by the use of a mechanical breaker. Both methods have their advantages, some preferring the one method, some the other.

In securing good quality in ketchup the same factors must be considered as in the making of pulp. These factors are care in manufacture and the use of a raw product of good color and quality. For discussion of these points in regard to pulp, see page 7.

The constituents used in the manufacture of ketchup in addition to the tomatoes are sugar, vinegar, salt, onions and spices. The sugar generally used is granulated cane or beet sugar. Some of the lower grades of cane sugar may be used satisfactorily. The terms used to designate grades of sugar below granulated do not always give a correct idea of the purity of the sugar and in buying such grades it is best to have samples submitted and have analyses made for sugar content.

The vinegar generally used is 100-grain distilled vinegar.