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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 Abb? 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

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 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.

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:

These samples were examined with the results given below.

The two products 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 , 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

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.

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 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 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.

Of especial interest is the refractive constant of the filtered liquor, shown in the last column of Table 2. The refractive constant of the various samples is much more uniform than might be expected from a product of this nature.

Table 2 is chiefly interesting as affording the data from which Tables 4 and 5 were calculated. The uniformity of the relations shown in Table 5 is such that it is usually possible from one determination on the filtrate and the determination of solids in the pulp by drying to distinguish pulp made from whole tomatoes from that made from trimming stock. For instance, if the specific gravity or index of refraction of a filtrate prepared from a pulp of unknown origin, and the per cent of solids in the pulp by drying, do not agree approximately with the relation between these determinations as shown in Table 5, it may be assumed that the sample was not prepared from whole tomatoes, or that some other substance, such as salt, has been added. Moreover, trimming stock pulp rarely conforms to the relations found in whole tomato pulp. For instance, the insoluble solids are usually higher and the acid lower in trimming stock pulp.

Trimming Stock Pulp

In Table 3 are given the results of the examination of 21 typical samples of trimming stock pulp prepared at different plants and in different localities. This table is of especial interest in showing that the relations between the results of the various analytical determinations differ from those of whole tomato pulps as given in Table 5. For instance, in No. 1470 the immersion refractometer reading is 45.90, and the per cent of solids is 9.54, whereas, according to Table 5, the per cent of solids in the pulp corresponding to an index of refraction of 45.90 should be 8.57. The specific gravity of the pulp is 1.0373, which, according to Table 5, should correspond to 8.98 instead of 9.54. Of course it cannot be said definitely that a pulp which on examination is found to conform to all the relations shown in Table 5 is necessarily whole tomato pulp. It is entirely possible for an occasional sample of trimming stock pulp to conform to all the relations shown in that table; moreover, the extent to which different samples of trimming stock pulp will vary from the relations shown in Table 5 differs with the manner of preparation. For instance, if a portion of the juice is discarded in the manufacture of trimming stock pulp, as is still the practice of some manufacturers, the variation from whole tomato pulp will be greater than otherwise and the variation will increase with the amount of juice discarded.

Methods of Analysis

These methods may also be applied to the examination of raw tomatoes and canned tomatoes. In applying the relations given below to the results obtained by the examination of tomato pulp or canned tomatoes, it is assumed that no substance such as sugar or salt has been added. If salt is found to be present in excess of the amount normal to tomatoes , it is necessary to determine the amount and make correction therefor before applying the relations given below.

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