TOMATO PRODUCTS: PULP, KETCHUP, AND CHILI SAUCE TEXT

NATIONAL CANNERS ASSOCIATION RESEARCH LABORATORY—Bulletin No. 21L. W. D. BIGELOW, Director Tomato Products Pulp, Ketchup and Chili Sauce BY W. D. BIGELOW and A. E. STEVENSON [Illustration] WASHINGTON, D. C. AUGUST, 1923 CONTENTS Pulp PAGE Introduction 5 Sanitary control of tomato pulp factories 6 Quality of product 7 Discarding tomato juice 8 Composition of tomato pulp 10 Whole tomato pulp 10 Trimming stock pulp 12 Methods of analysis 12 Microscopic examination 13 Determination of total solids 19 Determination of insoluble solids 32 Determination of sugar 32 Determination of acidity 33 Determination of salt 33 Determination of specific gravity 33 Importance of accuracy in the determination of specific gravity 50 Evaporation to definite volume of concentrated pulp 52 Ketchup Methods of manufacture 62 Factory control of the composition of Ketchup 63 Chili Sauce Methods of manufacture 72 TABLES Table 1, Composition of pulp and of the liquor separated from it 9 Table 2, Composition of whole tomato pulps 21 Table 3, Composition of trimming stock pulps 22 Table 4, Comparison of methods for the determination and calculation of solids in whole tomato pulp 23 Table 5, Tomato pulp and filtered liquor 24 Table 6, Corrections for specific gravity of hot pulp 43 Table 7, Comparisons of methods for determining specific gravity 45 Table 8, Corrections for specific gravity and Brix readings at different temperatures 55 Table 9, Equivalent volumes of pulp of different degrees of concentration 56 Table 10, Specific gravity and solids of tomato pulp 59 Table 11, Manufacture of Ketchup. Quantity of constituents to be added to 800 gallons of boiling, partly concentrated pulp 65 Table 12, Solids in Ketchup obtained by drying in vacuum at 70° C. and by Abbé refractometer from Geerlig’s table 68 Table 13, Refractive index and per cent solids in Tomato Ketchup 69 Table 14, Corrections for temperature to be used with Table 13 70 ILLUSTRATIONS Fig. 1. Small specific gravity flask 36 Fig. 2. Large specific gravity flask 36 Fig. 3. Special head and flask receptacles for Babcock milk tester 37 Fig. 4. Weight and specific gravity of tomato pulp 39 Fig. 5. Specific gravity cup for hot pulp 44 TOMATO PULP INTRODUCTION Tomato pulp is the fleshy portion of the tomato separated from skins, cores and seeds by means of a fine mesh screen and suitably concentrated by evaporation. During recent years great improvements have been made in the manufacture of tomato pulp and in the quality and appearance of the product. The care exercised in the selection of the raw material and in all steps of the manufacture of tomato pulp has been greatly increased. This is equally true of pulp marketed in small cans to be used as soup stock in private homes and of the pulp sold in larger containers for the manufacture of soup and ketchup. The large buyers of pulp have determined the grade or quality which gives them the best results in the manufacture of other products and the degree of concentration which they can use most economically. It is now customary, therefore, for large sales of pulp to be made on specifications, and it is impracticable to comply with such specifications without carefully controlling the manufacture of the product. The raw material must be so selected and the manufacturing operations so controlled that the color and flavor of the finished product is conserved. This is discussed briefly on page 7. If he desires to sell under specification, the manufacturer must comply with his contract with respect to specific gravity, and he cannot greatly exceed the specific gravity specified without substantial sacrifice in cost of manufacture. It is therefore economical to determine the specific gravity of the product as accurately as practicable (see p. 51) and also to adopt methods of manufacture that will control as closely as possible the specific gravity of the finished product. Beginning on page 33, methods are given for the determination of specific gravity under various conditions of manufacture and sale, and on page 50 is given the method for the determination of specific gravity of the cyclone juice or partly concentrated pulp which this laboratory has suggested as an aid to determining the volume to which the product should be evaporated to secure the desired specific gravity. This method has been used by a number of pulp manufacturers and found to be relatively convenient and practicable. It might be used to better advantage and to considerably greater profit if more help were employed—and some times more competent help—in determining specific gravity and controlling the point at which evaporation should stop. The importance and economy of accuracy in the determination of specific gravity is not fully appreciated by all, though some of the larger manufacturers are now giving much attention to that subject. This matter is discussed on page 50. There is included in the bulletin beginning on page =13= a detailed description of the Howard method for the microscopic examination of tomato products, and following that a detailed statement of the chemical and physical methods employed in this laboratory for their examination. Such methods are only of value to those trained in laboratory work. They are included here because the laboratory receives many requests for these methods from chemists employed by manufacturers of pulp. Men who are employed only for the tomato season find special need for such information. Our correspondence brings many inquiries regarding the percentage of solids in pulp of different specific gravities, and also regarding the relative values of pulp of different specific gravities. In Table 10 (p. 59) there is given in parallel columns the specific gravities of pulp of different degrees of concentration and corresponding percentage of solids, and it is a simple matter to calculate the volume which the same pulp would make if concentrated to any other specific gravity. This calculation is explained on page =54=—in discussing the point at which to stop evaporation to secure pulp of any desired specific gravity. This bulletin supersedes Bulletins 3 and 7, and also contains material which has appeared in several trade-paper articles prepared in this laboratory. These articles are extensively quoted and some of them are printed almost in full. Dr. F. F. Fitzgerald was the co-author of most of these publications and did much of the work on which they were based. He is therefore entitled to a substantial share of the credit for the material in this bulletin. SANITARY CONTROL OF TOMATO PULP FACTORIES The manufacture of tomato pulp requires careful supervision from beginning to end. The raw product must be carefully selected, and all possible steps should be taken to induce growers to discard rotting tomatoes in the field and to expedite the movement of the raw product from field to factory. Tomatoes must be carefully washed and sorted. It is only practicable to accomplish the latter by means of some type of sorting belt. Sorters should not attempt to trim. Their full attention should be given to the tomatoes passing by them. The sorter may place the tomatoes requiring trimming in a separate receptacle in order that they may be carried to a table not provided with a moving belt and handled by special trimmers. Conveyors, receptacles and machines must be constructed and installed with a view to convenience in cleaning. Care must be taken to expedite the manufacture of the product in every way possible in order to give no opportunity for bacterial growth during the process of manufacture. The brief comments given above are offered by way of reminder. This important subject is not further discussed because it has been adequately treated by Mr. B. J. Howard of the U. S. Bureau of Chemistry in bulletins which are readily available. These bulletins are designated as Bulletins 569 and 581, respectively, of the United States Department of Agriculture. They may be secured by requesting them of the Superintendent of Documents, Government Printing Office, this city, and enclosing five cents in coin for each copy desired. All manufacturers of tomato pulp will do well to study these bulletins and have them studied by their responsible employees. QUALITY OF PRODUCT There is a growing tendency to give increased attention to the quality of tomato pulp. The tomatoes should be ripe and well colored. Green tomatoes or tomatoes with green portions not only do not have the requisite amount of red coloring matter but they contain material which masks and dulls the color of fully ripe tomatoes. There is a difference of opinion among successful manufacturers of pulp regarding the relative color of pulp manufactured after hot or cold cycloning. Some maintain that a better color is obtained by cycloning hot. Others, apparently equally skilled and able to manufacture an equally good product, maintain the reverse. Much depends on the control of the cyclone—the setting of the paddles and the speed at which they are operated. The evaporation should be as rapid as possible. The operation of the kettles in such a way that the pulp burns on the kettles or on the coils damages the flavor of the product and impairs its color. The pulp should be cooled promptly after processing, or if that is not practicable should be stacked loosely so that the cans will have ample ventilation until they are entirely cooled. Pulp packed in five-gallon cans is rarely processed. It should, however, be filled into the cans at a temperature of at least 180° F. It is best to give pulp in No. 10 and smaller size cans a short process in boiling water. With pulp filled at 180° F., ten or fifteen minutes is a sufficient cook. Pulp filled at lower temperatures or which is allowed to partially cool before processing requires a longer process. In order to protect the color it is best to water cool No. 10 cans of pulp after processing. Pulp in cans of any size should not be stacked solid while it is still hot. The metal of the can has a bleaching action on the pulp and this is greatly increased if the pulp is stacked hot or stored in a hot warehouse. If stacked while excessively hot, stack-burning may occur with consequent darkening of the pulp. As indicated above, there is a considerable difference of opinion among successful manufacturers of pulp regarding the details of manufacture necessary to secure the best results. It is probable that different conditions call for different methods of operation. At any rate, all successful manufacturers are agreed that the color of the pulp is an important index to its quality and greatly influences its commercial value. The flavor of pulp is also an important criterion and is considered by many buyers in forming an estimate of the value of pulp. A scorched taste or a flat flavor show that the manufacture of the pulp was not adequately controlled and impairs the commercial value of the product. Color and flavor commonly go together. The same manufacturing methods which yield a product of high color are likely to give a product of superior flavor. DISCARDING TOMATO JUICE It was formerly customary, and is still the practice of some manufacturers of tomato pulp, to discard a portion of the juice of the tomatoes. Some manufacturers, especially in the preparation of pulp from tomato trimmings, allow the trimmings to pass over a colander and thus separate the free juice, which is discarded. Others allow the product of the cyclone to stand for a time in tanks and then discard the clear juice which settles in the bottom of the tanks. Both practices are wasteful and have generally been discontinued. Some still adhere to one or both, however, and it was thought best to make the matter the subject of study. Some discard the juice because of the belief that it consists of nothing but water and is valueless. Some are of the impression that the juice separated from the trimming stock before straining takes on a brown color during evaporation which would interfere with the red color desired in the finished product, if allowed to go into the pulp. Some recognize the value of the juice, but believe that the expense of its evaporation would not be warranted by the increased quantity of pulp. Some have not measured the juice discarded and greatly underestimate its volume. With the view of determining the approximate value of the material discarded in this manner, a batch of material, fresh from the cyclone, was divided into two portions, one of which was immediately concentrated to form a pulp, and the other was allowed to stand about 20 minutes when a clear liquor had separated at the bottom. This clear liquor was then removed and the remainder evaporated until the desired consistency was obtained. Samples of the finished pulps, of the raw product from which each was prepared and of the clear liquor, separated from the second one, were preserved by sealing in cans and processing. These samples were numbered as follows: 702—Product from the trough under the second cyclone, or finisher. 703—Clear liquor, which separated at the bottom of the tank, after a portion of 702 was allowed to stand. This formed about one-fourth of the entire product of the tank. 704—Drained residue from 703. 705—Finished pulp obtained by concentrating 704. 706—Finished pulp obtained by concentrating 702. These samples were examined with the results given below. TABLE 1.—_Composition of Pulp and of the Liquor Separated from It_ =================================================================== Sample | Total |Insoluble| Ash | Sugar | Acid | Undetermined Number | Solids | Solids | | (as | (as | Organic | | | | Invert)| Citric)| Matter -------+--------+---------+--------+--------+--------+------------- | _Per | _Per | _Per | _Per | _Per | _Per Cent_ | Cent_ | Cent_ | Cent_ | Cent_ | Cent_ | 702 | 4.38 | 0.40 | 0.34 | 2.27 | 0.29 | 0.87 703 | 3.84 | 0.10 | 0.38 | 2.32 | 0.29 | 0.75 704 | 4.47 | 0.50 | 0.38 | 2.31 | 0.31 | 0.77 705 | 9.17 | 1.83 | 0.78 | 4.07 | 0.51 | 1.87 706 | 7.85 | 0.98 | 0.69 | 3.51 | 0.46 | 2.04 -------+--------+---------+--------+--------+--------+------------- The two products (705 and 706) were evaporated under exactly the same conditions and to what appeared to the operator to be the same consistency. After cooling, however, it was apparent that while the body of the two finished products was apparently equal, the consistency of No. 706 was superior to No. 705 in that the former was smooth and creamy, whereas the latter had a somewhat irregular, lumpy appearance. This difference was doubtless due to the greater content of soluble solids in No. 706. The color of the two samples was identical. A mixture of one part of No. 703 and three parts of No. 704 when evaporated in the laboratory to the same consistency was identical in every way with No. 706. From the composition as stated in Table 1 it is apparent that the flavor and food value of the clear juice, which is sometimes discarded (represented in No. 703), are practically identical with the unconcentrated pulp as it passes through the cyclone. In fact, the only difference between the two appears to be about one-half per cent of insoluble matter. When the product is allowed to separate, it seems probable that this insoluble material as it rises in the mass has a tendency to act like a filter and carry up with it a large proportion of the bacteria and moulds present. The scale on which the work was done did not permit of sufficiently accurate measurement of the finished pulp to warrant the calculation of the loss in quantity caused by discarding the juice. From the composition of the pulps and of the raw material, however, it is apparent that this loss is practically proportional to the percentage of juice discarded. It is apparent, therefore, that the evaporation of the material just as it passes through the finisher will yield a product of the same color, of better consistency, in considerably greater quantity, and at practically the same proportionate expense of concentration as the evaporation of the residue after discarding the juice in accordance with the custom mentioned above. COMPOSITION OF TOMATO PULP[1] Whole Tomato Pulp The results obtained by the examination of 33 samples of whole tomato pulp are given in Table 2. The concentration of the samples varies from unconcentrated pulp as it runs from the cyclone to pulps of very heavy consistency. This table contains the data from which Tables 4 and 5 were calculated, although during the season a partial analysis was made of a large number of other samples, and the data secured therefrom were in all respects confirmatory of the relations calculated from Table 2. [1] This chapter is taken largely from an article by Bigelow and Fitzgerald, published in the Journal of Industrial and Engineering Chemistry, 1915, vol. 7, page 602. In addition to the data obtained by the various determinations, Table 2 gives the relation between the results of the determinations for each individual sample. For instance, the ratio of pulp solids to filtrate solids (pulp solids divided by filtrate solids) varies in the different samples from 1.091 to 1.154, and, with the exception of two samples, it varies from 1.100 to 1.145. The average of the 33 samples was 1.12. The relation of insoluble solids to total solids (expressed as per cent of insoluble solids in total solids) is shown in Table 2. Considering the variations in the methods employed by different manufacturers in the preparation of tomato pulp, the per cent of insoluble solids in the total solids as shown by this column is closer than we might expect, varying in most of the samples from 11 to 14 per cent. The per cent of sugar in the soluble solids, as shown by Table 2, varies in most of the samples from 50 to 55 per cent. This figure cannot be expected to be constant in different localities and in different years. The acid, estimated as citric, constitutes in most of the samples from 9 to 10 per cent of the soluble solids.