TOMATO PRODUCTS: PULP, KETCHUP, AND CHILI SAUCE TEXT

strongly advisable to cool the pulp under conditions that prevent evaporation before determining specific gravity. The importance of accuracy in the determination of specific gravity in tomato pulp is discussed on page 50. Methods are given below for the determination of specific gravity in both hot and cold pulp. When salt has been added, the amount should be determined and a correction applied by deducting .007 from the specific gravity for each per cent of salt present. (a) <sc>COLD PULP AFTER CENTRIFUGING TO ELIMINATE AIR BUBBLES</sc> This method may be employed for pulp of any degree of concentration or for unconcentrated cyclone juice. A specific gravity flask such as is shown in Figure 1 is used together with a “2-bottle” Babcock milk tester (the centrifuge referred to below). The flask may be obtained of Eimer & Amend, Third Avenue, 18th to 19th Streets, New York City, or of Emil Greiner & Co., 55 Fulton Street, New York City, and in ordering it should be designated as “specific gravity flask for tomato pulp of Pyrex glass with a capacity of about 125 cc.” The “2-bottle” Babcock milk tester may be obtained of any dairy supply house. It may also be obtained of any dealer in chemical apparatus by designating it as E. & A. No. 1833. The specific gravity flask may be calibrated as follows: Obtain the weight of the flask after thoroughly cleaning and drying, fill to overflowing with water (preferably boiled and cooled distilled water) and remove the excess water from the mouth of the flask by means of a straight edge. Wipe dry and weigh immediately. If the flask full of water is weighed at any other temperature than 20° C. (68° F.) a correction must be made to obtain the weight at that temperature. These corrections are as follows: ============================================= Temperature |Correction to be added |with flasks having a | volume of— ----------+----------+------------+---------- Fahrenheit|Centigrade| 125 cc. | 400 cc. ----------+----------+------------+---------- | | _Grams_ | _Grams_ 69 | 20.6 | .02 | .05 70 | 21.1 | .03 | .09 71 | 21.7 | .05 | .14 72 | 22.2 | .06 | .20 73 | 22.8 | .08 | .25 | | | 74 | 23.3 | .09 | .30 75 | 23.9 | .11 | .35 76 | 24.4 | .13 | .41 77 | 25.0 | .15 | .47 78 | 25.6 | .17 | .53 | | | 79 | 26.1 | .18 | .59 80 | 26.7 | .20 | .65 81 | 27.2 | .22 | .71 82 | 27.8 | .24 | .77 | | | 83 | 28.3 | .26 | .83 84 | 28.9 | .28 | .89 85 | 29.4 | .30 | .96 86 | 30.0 | .32 | 1.02 ----------+----------+------------+---------- If it is desired to use somewhat larger samples and thus secure correspondingly more accurate results, a similar flask, but made somewhat larger (capacity approximately 400 cc.), may be employed. Such a flask, with a diameter of a little over 3 inches, is illustrated in Figure 2. This larger flask will not fit into the Babcock tester, and when it is used a special head for the Babcock tester must be made. Such a head is illustrated in Figure 3, and can be made by any good tinner. The larger flask shown in Figure 2 holds a heavier weight than the Babcock machine is intended to carry, and the advisability of its use is perhaps questionable. In any case, whatever size flask is used, it is important to build a guard around the centrifuge in order to protect the operator when the apparatus gives way, as it eventually will. [Illustration: Fig. 1. Small Specific Gravity Flask. Fig. 2. Large Specific Gravity Flask. Dimensions given are outside measurements. Thickness of walls is about 3/64 in.] The details of the method of determining specific gravity by the use of this apparatus are as follows: Fill the flask shown in Figure 1 with the sample of pulp and place in the centrifuge (the Babcock milk tester mentioned above). Place a suitable counterpoise[16] in the other receptacle of the centrifuge. Whirl for from one-half to one minute at a speed of about 1,000 revolutions per minute, that is with the handle turning about 100 revolutions per minute. Because of the air bubbles removed by whirling, the surface of the pulp will now be considerably below the top of the flask. Fill the flask and whirl in the centrifuge again. Repeat this filling and whirling until the flask is practically full of pulp after whirling. Ordinarily two or three separate whirlings are sufficient. Then add a few more drops of pulp so that the pulp comes above the top of the flask, and strike off flush with the top of the flask with a straight edge. Wash the outside of the flask, wipe dry, and weigh. Then read the specific gravity of the pulp from a table prepared, giving the weight of the flask full of pulp and the specific gravity of the pulp in parallel columns, or calculate the specific gravity as described below. [16] This counterpoise may be prepared with a can or bottle weighted with some heavy material such as solder or shot, until it balances approximately the weight of the can full of pulp. The counterpoise, once prepared, may be left in the centrifuge. [Illustration: Fig. 3. Special Head and Flask Receptacles for Babcock Milk Tester.] While the weight is being taken a thermometer may be placed in the pulp remaining in the can or dipper from which the flask was filled. If the temperature varies from 68° F. the specific gravity may be corrected by Table 8. In order to use this method the temperature of the pulp should not be below 50° F., or above 86° F.; otherwise, it should be warmed or cooled, as described above. The method is accurate, simple, easily operated and fairly rapid. To calculate the specific gravity from the weights obtained, the weight of the clean, dry flask and of the water it contains at 68° F. are necessary. The weight of the clean, dry flask is then subtracted from the weight of the flask full of pulp to obtain the net weight of the pulp. This divided by the weight of the water the flask will contain at 68° F., gives the specific gravity. A table can be constructed readily for each flask, which will give in parallel columns the weight of the flask full of pulp and the corresponding specific gravity. This greatly simplifies the determination, as it eliminates all calculation. When such a table is employed a balance giving actual weights is practically as convenient as one reading specific gravity directly. It has the very important advantage that the balance, weights, and flask may be tested from time to time. In preparing such a table it is convenient first to draw a curve representing specific gravities of the pulp and corresponding weights of the flask full of pulp of various degrees of specific gravity. The table may then be constructed from the curve. For instance, let us suppose that the flask weighs 56.00 grams and that when full of water at 68° F. (20° C.) it weighs 176.63 grams. The water contained at the temperature mentioned then weighs (176.63 - 56.00) 120.63 grams. Now the specific gravity of the pulp is its weight compared with the weight of an equal volume of water. Having the figures given above we can easily calculate the weight of the flask filled with pulp of any desired specific gravity. We may therefore calculate the weight of the flask plus pulp of two different specific gravities; mark those points on a sheet of coordinate paper with specific gravity of the pulp entered at the bottom and the weight of flask plus pulp at the side, and a straight line drawn through the two points mentioned gives us the weight of the flask when filled with pulp of any specific gravity. For instance, if the flask mentioned above be filled with a pulp of the specific gravity of 1.03, the weight of the pulp is (120.63 × 1.03) 124.25 grams. This added to the weight of the flask (56.00 grams) gives us 180.25 grams. Similarly, if the flask be filled with pulp of 1.04 specific gravity the weight of the contents at 68° F. will be (120.63 × 1.04) 125.46 grams. This added to the weight of the flask (56.00 grams) gives 181.46 grams as the weight of flask plus pulp. Now if a sheet of coordinate paper be prepared with specific gravities entered at the bottom and weight of flask plus pulp at the side, these points may be entered. This is done in Figure 4 and the two points mentioned are each indicated by a circle and are connected by a straight line. A table may be constructed from this line, giving the weights of flask plus pulp in one column and the corresponding specific gravity in another. [Illustration: Fig. 4. Weight and Specific Gravity of Tomato Pulp.] As an illustration of this there are given below a series of figures illustrating the beginning of the table that could be constructed from Figure 4. If a large sheet of coordinate paper be taken the line shown in Figure 4 may be extended so that a table may be constructed for pulp of all concentrations. ---------+-------- Weight of|Specific flask and|gravity pulp | ---------+-------- 180.25 | 1.0300 180.31 | 1.0305 180.37 | 1.0310 180.43 | 1.0315 180.49 | 1.0320 180.55 | 1.0325 180.61 | 1.0330 180.67 | 1.0335 ---------+-------- The highest degree of accuracy can be secured by filling the flask and making the weighing at exactly 68° F. This is obviously not practicable under factory conditions, however, and satisfactory results can be secured by taking the temperature of the pulp at the time of weighing and correcting for temperature by the use of Table 8. This table gives the correction to be added to the specific gravity when the pulp is taken at temperatures between 68° and 86° F., and the correction to be deducted from the specific gravity for temperatures, between 55° and 68° F. As a matter of principle, correction factors should be avoided as far as practicable, and the smaller the correction factor the more accurate the results will be. This table will be found especially useful in determining the specific gravity of the partly concentrated pulp, as is directed on page 50. As stated above, in determining specific gravity by this method it is advisable that the reading be made to the second place of decimals. For this purpose an assay pulp balance is suggested. An assay pulp balance carrying a maximum load of 300 grams is listed by dealers in chemical apparatus at $52.50. This balance may be obtained from dealers in chemical apparatus by designating it as “Assay pulp balance E. & A. No. 292, capacity 300 grams.” The same balance, more heavily built, and preferable for that reason, carrying a maximum capacity of 600 grams, is listed at $63. A satisfactory set of weights, suitable for weighing a cup similar to that shown in Figure 1, may be obtained from any dealer in chemical apparatus by designating it as E. & A. No. 516, “Metric brass weights in wooden box, 200 grams to 1 centigram.” This is listed at $5.50. For convenience, all of the apparatus necessary for using this method of determining specific gravity is listed below. With the exception of the specific gravity flask this apparatus may be purchased of any dealer in chemical supplies. The specific gravity flasks have not heretofore been available except through this laboratory, which purchased a considerable quantity of them and supplied them to manufacturers of pulp as long as this supply lasted. At the urgent request of the writer, Eimer & Amend and Emil Greiner & Co., both of New York City, have finally stocked this item and stand ready to supply it to those wishing to secure it. Specific gravity flask for tomato pulp, of Pyrex glass, 1½ × 6¼ inches (outside measurements), capacity about 125 cc. Two-bottle Babcock milk tester, with 2 brass holders, E. & A. No. 1883. Assay pulp balance, maximum load 300 grams, E. & A. No. 292. Metric brass weights in wooden box, 200 grams to 1 centigram, E. & A. No. 516. Chemical thermometer, 50 to 212° F.[17] [17] If it is preferred a chemical thermometer with Centigrade scale may be used having a range of from 0 to 100 degrees. (b) COLD PULP WITHOUT CENTRIFUGING A method frequently employed for determining the specific gravity of cold pulp is to fill the cup by pouring, strike off with a straight edge, wash the outside, dry and weigh. As ordinarily practiced, this determination is attended by considerable error. If the balance is arranged for reading specific gravity directly, weights should be at hand for determining the accuracy of the balance and the weight of the flask, and both should be checked from time to time. The pulp on being poured into the flask or cup carries with it air bubbles to such an extent as to materially reduce the weight. Attempts to remove these air bubbles without the use of a centrifuge have not been successful. This is shown in Table 7, in the column headed “Pouring cold and whirling by hand.” The figures given in this column were obtained by weighing the sample after it had been whirled vigorously in the cup shown in Fig. 5 until air bubbles appeared to be eliminated. From 50 to 175 revolutions were given the cup in each of the determinations whose results are shown in this column. Even then it will be noted by comparison with Column 1 that the results are low. As the method is ordinarily practiced in the plant, without any attempt to remove the air bubbles by whirling, the results obtained are likely to be less accurate than those shown in the column just mentioned. (c) SPECIFIC GRAVITY OF HOT PULP Many manufacturers of tomato pulp control the concentration of their product by determining specific gravity when the evaporation is almost completed. They therefore desire the results at the earliest possible moment, and there is no attempt to cool the sample before determining specific gravity, although in that way much more accurate results could be obtained. When necessary to use this method the hot pulp is poured into the specific gravity flask (Fig. 1 or Fig. 2) by means of a dipper until the flask overflows. The top is then “struck off” with a straight edge and the flask placed in a shallow basin of water and the pulp carefully washed from the outside. The temperature of the pulp remaining in the dipper is then determined by means of a chemical thermometer. The flask is then dried with a towel, which operation is greatly facilitated by the heat of the pulp. The cooling of the contents of the flask causes contraction, so that after washing the flask is not entirely full. This should be disregarded, as it is desired to determine the weight of the amount of pulp that filled the flask originally. As soon as the outside of the flask is clean and dry the flask and contents are weighed. 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. [Illustration: Fig. 5. Specific Gravity Cup for Hot Pulp.] 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 ------+---------------+---------------+---------------+--------------