Part 3

The keeping quality after opening depends upon the utilization of the same principles followed in the household operation of making fruit butters, ketchup, preserves, and pickles, that is, sufficient concentration and the use of sugar and vinegar. A ketchup can be made essentially a pickle with an excessive quantity of vinegar and it will keep; it can be made a preserve with excess of sugar and it will keep; or, it can be made a distinctive sauce well concentrated in which the vinegar and sugar are used only in sufficient quantity to give proper flavor, and it will keep. Apple juice or cider will spoil quickly if allowed to stand in a warm place; apple sauce will behave in like manner only a little more slowly; but if the juice and sauces be boiled together until they have acquired the consistency or state known as apple butter, they will keep very well. The acidity, sugars, and solids have been increased by the concentration. In the making of tomato ketchup, the fruit does not have sufficient acidity and sugar of itself to give preservative property at the concentration desired for a sauce, so these are augmented by the addition of vinegar and sugar.

A great deal of stress has also been placed upon the effect of the spices in acting as preservatives. Experiments have demonstrated conclusively that when these are used in the small quantities required for flavoring, that their effect is practically nil. The active principles of the spices are effective only when present in the proportion of 1 to 500 or 600 and in ketchup the proportion is only 1 to several thousand. Likewise the quantity of salt is too small to have effect.

The keeping qualities of a mild ketchup will depend far more upon the sterilization than most manufacturers realize. It is easy to make almost any ketchup apparently keep while the bottle is unopened. The spoilage after opening is most often observed to be due to mold which has been assumed to come from infection from the air. As a matter of fact, this is nearly always due to spores which have been held in abeyance, due to lack of air while in the bottle, and which begin growth as soon as conditions are favorable. Spores which fall into the bottle from the air might be unable to germinate upon such a medium, while those already present would.

CHARACTERISTICS OF COMMERCIAL KETCHUP.

While tomato ketchup is a complex and variable product, its general composition may be determined with a fair degree of accuracy. Inspection will give a good idea of color, consistency, smoothness of body, fineness of finish, tendency to separate, presence of objectionable particles, and evidence of gross fermentation. The odor and taste will give a clue to the kind and quantity of spices used and to a certain extent the character of the raw material. Judging by odor and taste is not so well done as judging by the eye by most persons. The education of those two senses has been neglected and therefore fail to give all the information which might be acquired in this way.

A chemical examination which will give the specific gravity, total and soluble solids, sugar, salt, and total and volatile acidity, will be sufficient to give a good idea of the stock used—tomato, salt, sugar, and vinegar, but not the spices. A microscopic examination will assist in determining the condition of the material used and whether decomposition has taken place before or after manufacture. The facts obtained through these sources will permit of classifying commercial ketchup with a fair degree of accuracy.

There has been a very marked change in the character of ketchup since the transition from the preservative to non-preservative goods, not only microscopically, but also in composition. Formerly, there were very many brands of thin liquid ketchup, showing little concentration of pulp, very low in sugar, and having only small quantities of vinegar; the standard was bulk rather than quality. The microscopic examination also showed that the product had frequently undergone change before and after preparation. Recent examinations show that there has been a very marked improvement; that the body is decidedly heavier, more sugar and vinegar are used, the tissue is cleaner, and there are fewer organisms present, also that the difference in composition in preservative and non-preservative ketchup is small, whereas, formerly it was marked.

The variations found in ketchup of rather recent examination show in the non-preservative kind the specific gravity varied between 1.091 and 1.177; the solids between 19 and 37 per cent; the salt between 2 and 4 per cent; sugar between 12 and 29 per cent; and volatile acids between .54 and 1.24 per cent. In the preservative kind, the specific gravity ranged from 1.032 to 1.120; the solids from 9.23 to 28 per cent; salt, 1.48 to 3.4 per cent; sugar, 4.95 to 16.9 per cent; and volatile acidity, .16 to .64 per cent. As a class they averaged lower in concentration of tomato and in sugar and vinegar, though if proper sterilization had been used, some of them would have kept without difficulty. In experimental work it was found that a ketchup concentrated so that when finished it showed an added sugar content of 15 per cent or more, a total acidity of 1.2 per cent, and a specific gravity of 1.120 or more, that it would keep. To obtain a total acidity of 1.2 per cent means the addition of about .4 to .6 per cent acidity in the vinegar used. However, there are brands of ketchup on the market which keep well after being opened and which have a total acidity of less than 1.0 per cent.

The manufacturer can use the following as a starting point for non-preservative ketchup; pulp, 100 gallons; sugar, 60 pounds; salt, 8 pounds; vinegar, 100 grain, 2 gallons; spice to flavor; and concentrate to 50 to 55 gallons.

MICROSCOPIC EXAMINATION.

A discussion of the microscopic appearance of ketchup in terms which can be readily understood by manufacturers is not an easy task, as it necessarily involves technical knowledge. The subject has become one of importance, owing to the attitude of many food officials in enforcing a microscopic standard for this product, and on the part of many brokers in requiring a guarantee to comply with this standard in making purchases. Many manufacturers have either assumed or found it necessary to have their finished products examined. Some employ “experts” to make the examinations in their own plants, while the majority send their samples to commercial laboratories. The total tax upon the industry for such work amounts to thousands of dollars annually. The result of the work as a whole has been beneficial, as any effort is which attracts attention to details. It has likewise been the means of causing much unpleasantness and not infrequently loss, because of lack of understanding on the part of both manufacturer and examiner as to the cause of certain findings. The manufacturers have proceeded in the usual way without sufficient knowledge of what the resultant product will be unless there is careful supervision of material and methods, while too frequently the examiner is neither experienced in technique of the examination nor in the effects of the different steps in manufacture upon the product. Furthermore, much distrust in microscopic finding is evinced when a half dozen or more samples from the same batch, sent to as many persons, result in as many different reports. It naturally causes a lack of confidence in both paid examiners and in food officials, though those who make these examinations may be absolutely honest in their findings. In order to clarify some of the points, it has become necessary to go into detail, into both the method of examination and into the effect produced by manufacture.

A scientific method of food examination is necessary for food officials in order to determine the condition of a product, but is not necessary for the manufacturer, though it may be advantageous. The latter is in a position to know what enters his factory and what changes take place in the food until it reaches the sealed package. He should have no fear of a method which correlates the findings in the finished product with that of the material used and the changes due to treatment.

Undue importance may seemingly be given to the subject of ketchup, but the principle involved applies as well to other products.

The fundamental basis for the microscopic examination of any food product must depend upon the structure of the material which enters into its composition. Any attempt to determine an abnormal condition, such as decomposition, without a knowledge of the normal, must necessarily be of little value. There is some work which can be done in a mechanical manner by almost anyone capable of looking through a microscope, and if the work is properly supervised, it may have a value, but the lines along which this can be done are very limited. Any attempt to apply such superficial methods to the general examination of food products can not properly protect the public and may be unfair to the producer. It has, therefore, been deemed advisable to incorporate a brief statement concerning the structure of the tomato before discussing the resultant products.

HISTOLOGY OF THE TOMATO AND OF THE RESULTING KETCHUP.

STRUCTURE OF THE TOMATO.

=Pericarp.= The tomato is a typical berry, the ovary wall, free from the calyx, forming the fleshy pericarp, which encloses chambers filled with a clear matrix, containing the seeds. The pericarp consists of an outer tough membrane, the epidermis, a more or less thick layer of parenchyma tissue, the pulp, and an inner thin, delicate membrane, the lining layer of the loculi or chambers in which are the seeds. The epidermis consists of a single layer of cells which have a very thick continuous cuticle about one-half of the diameter of the whole cell. The cuticle differs in chemical composition from the rest of the cell walls, being impervious to water, and resisting rotting longer than do the cellulose walls. As it is continuous over the whole of the fruit, the skin can be readily separated from the other tissues. Hot water facilitates the removal of the skin, as it causes the cellulose of the walls to swell more than the cuticle, producing an effect as of shrinkage of the outer wall and a consequent curling of the skin. The radial walls of the epidermis are short and irregularly thickened, leaving pits in the walls, and giving them a beaded appearance. The skin constitutes about 1.3 per cent of the tomato.

The layers of parenchyma just beneath the epidermis are closely united and flattened, with their adjoining walls irregularly thickened. On account of their position, they are called hypoderm. In the tomato the hypoderm consists of two or three layers of cells, parts of which usually separate with the epidermis. Below these cells are the thin-walled parenchyma cells, which are approximately globular, vary considerably in size, are very loosely held together, and have many intercellular spaces. These cells constitute the mass of the pulp, and with the juice constitute 96.2 per cent of the tomato.

The layer of cells which lines the chambers has the typical leaf epidermal structure, the wavy outlines, the hollows and protuberances of adjoining cells fitting one another so that they form a continuous layer. They are also flattened laterally. The structure can be understood readily when it is known that the pericarp is really a metamorphosed leaf and that the outer side of the leaf forms the inner wall of the ovary.

The chambers of the tomato are filled with a clear, slimy matrix in which the seeds are embedded. The matrix consists of parenchyma cells of various sizes and with delicate walls, and a small nucleus. The cells are massed loosely, and can be separated readily. In those cells, as well as in the wall cells, are starch grains which vary in size, being round or approximately so, and having the hilum, when visible, a straight line to one side of the center.

=Coloring Matters.= In the parenchyma cells are two coloring matters, one yellow, which is amorphous in structure, and the other red and of crystalline form. The sap contains a yellow color in solution which differs in its reactions from those in the pulp.

=Red Color in Tomatoes.= The red coloring matter in tomatoes is in the form of irregularly shaped crystal-like chromoplasts, which occur in masses of various sizes. They are present in largest amounts usually in the protoplasm which lies close to the ectoplasm and in that surrounding the nucleus. They vary from sharp, bright-colored forms to those more or less blunt in outline, and dull in color. They may be situated largely in the periderm, the soft parenchyma beneath the periderm, or through the whole mass of the parenchyma with the exception of the matrix surrounding the seeds in the loculi. In tomatoes having the color in the periderm a considerable amount is lost by adherence to the skin. The chromoplasts are not affected by rotting to the same extent as are the other constituents of the cell; they can be found floating free in the debris from rotted cells, still retaining considerable color. They lose their color gradually, in some varieties much more rapidly than in others. In stored pulp which has fermented, the color may be faded to a dull yellowish brown. In tomatoes intended for ketchup where a bright red color is desirable, care should be used in the selection of a variety having the chromoplasts bright, properly oriented, and in sufficient quantity.

=Vascular Bundles.= In the pulp of the tomato are found strands of vascular tissue, entering from the stem, and dividing and ramifying through the soft pulp. These consist of long tubes with thin walls, some of which have a strengthening band in spiral form on their interior walls, the associated cells being without any special marking. The strands vary in size from those having a few tubes to those having a large number.

=Seeds.= The seeds of the tomato are small, flattened, yellow bodies covered by a clear gelatinous membrane. Their peculiar characteristic is the out-growth of hairs of varying lengths. The seeds constitute about 2.5 per cent of the weight of the tomato.

STRUCTURE OF KETCHUP.

Although the tomato pulp is broken into fine particles by the action of the cyclone, and the skin and seeds are removed by the fine sieves, pieces of the various tissues can be readily identified. The skin and seeds have characteristics which would serve to distinguish them from similar parts of other vegetables which might be used for adulteration, but particles of skin and hairs from the seeds are rarely found. The distinctive features which can be relied upon are the red, irregularly-shaped, chromoplastic bodies in the parenchyma cells, and the peculiar wavy-outlined cells of the lining layer of the chambers. As nearly all young vegetable tissues have spiral vessels in their vascular strands, these are not distinctive, except that they might differentiate similar tissues of different size. There is very little starch in mature tomatoes, and moreover, as the cooking causes the starch to swell and lose its structure, the starch could not be used for identification.

Good ketchup made from whole tomatoes, in spite of the minuteness of the particles, has a clean appearance, and can be readily distinguished from poor ketchup. All ketchup will have some micro-organisms present, as it is practically impossible to free the tomatoes from them in the washing, but the number is very small in some of the best, in the manufacture of which careful washing and sorting have been done. The poorer the ketchup, usually, the greater number of organisms—bacteria, yeasts, and molds; sometimes one form predominating, sometimes all three being in great abundance, this latter condition usually prevailing in the poorest ketchup, where more or less rotting has occurred.

As the tomato pulp is a favorable medium for certain organisms, these will develop first, and it has also been determined that while one organism is developing vigorously, others present are checked until the activity of the first ceases. Then again, as the composition of the pulp is being altered by the development of the organisms, the changes induced render it a more suitable medium for other organisms which are present but held in abeyance, so that pulp which has been allowed to stand for some time will usually have present not only a large number, but also different kinds of organisms.

CHANGES PRODUCED IN PULP BY ROTTING.

When tissue is held and allowed to rot spontaneously, the pulp is decomposed into a granular, watery mass. The cells beneath the epidermis are the finest and driest in the sound tomato, considerable pressure of the cover-glass being required to separate them for examination. Even when forced apart, the cells retain their shape. They contain a delicate semi-transparent protoplasm with a rather large nucleus surrounded by protoplasm and having strands from this mass connect with the protoplasm lining the wall. Pieces of the same tissue, on having the skin removed so as to expose the broken tissue to the air, were covered with mold in one day and in three days so badly disorganized that the cells separated with the weight of the cover-glass. The cells were transparent, the walls collapsed into a wrinkled mass, the protoplasm had disappeared, except a skeleton of the nucleus, but the red chromoplastic masses were intact. The middle lamella of the cells is the part which dissolves first, allowing the cells to separate and causing the walls to become thinner. The cell cavity is often filled with bacteria, so that the effect of the rotting can not be seen until the cells have been washed thoroughly. These bacteria have been mistaken for the particles left by the decomposition of the cell contents. The vascular bundles are surrounded usually by small parenchyma cells which do not separate readily from the strand in the healthy tissue, but in the decayed tissue the vessels can be seen clearly, free from other tissue. In advanced stages of rottenness the walls of the vessels may be dissolved, leaving only the spiral thickening, and the parenchyma tissue crumbled into powder-like fragments. The parts of the tomato which resist rotting the longest are the skin, which may be washed clean of adhering particles, the spirals of the vessels, and red particles of the chromoplasts.

The conditions found in the rotted sections and pieces of tomato can be distinguished in the poor ketchup and these factors, together with the large number of organisms present, serve for purposes of differentiation.

ORGANISMS IN KETCHUP.

Tomato pulp furnishes a medium suitable for the development of many organisms, as it contains all of the necessary food elements. The raw pulp has an acidity of from 0.2 to 0.4 per cent usually, though there may be variation due to fermentation and other causes. On account of its mild acidity, it is especially suitable for the development of many yeasts and molds, and some forms of bacteria, consequently there is present a varied and abundant flora if the pulp be held for an appreciable time before using, or if it has been made from tomatoes not properly sorted and washed. Where the black rot occurs on tomatoes, the tissue is hardened like cork, and if not removed on the sorting belt, is broken into small pieces by the cyclone, and appears as black specks in the ketchup, these being readily perceived by the naked eye. The white rot forms soft spots, which, though not so prominent as the black, carry much more contamination, as, apart from the bacteria, yeasts, and molds present, they are often swarming with Protozoa. These are not ordinarily recognized in the ketchup, as a chemical or physical shock causes them to contract, assume a spherical shape, and become motionless. In this condition they resemble the immature conidia of some of the molds. Rarely only one organism predominates in pulp from rotted fruit, then the rot consisting of a nearly pure culture. In all cases of soft rot, there is much more contamination carried, as the organisms are small and a greater number present in a given area. Whenever the inner tissue of tomatoes is exposed, organisms develop rapidly, the forms varying with the locality and the conditions in the pulp. Some of these organisms may survive the treatment of the pulp when converted into ketchup, or the original organisms may be destroyed, and a different set gain access and develop, but in either event all the organisms alive or dead which were present at the period of manufacture are found in the ketchup. It has been noted that certain brands of ketchup have predominating organisms present which are practically constant from year to year.

A method for the microscopic examination of ketchup in order to determine the number of organisms present is described in Circular No. 68, Bureau of Chemistry. It consists in an adaptation of a method used in examining blood in physiological and pathological work, and of yeast in the brewing, wine-making, and distilling industries. The outfit required consists of two parts, the microscope and the counting chamber, each with minor accessories. The optical outfit recommended for food examination consists of a microscope with eye pieces and objectives which will give approximate magnifications of 90, 180, and 500 diameters. It is advised that these magnifications be obtained by using 16 mm and 8 mm apochromatic objectives, and ×6 and ×18 compensating oculars (×6 ocular and 16 mm objective equals ×90; ×6 ocular and 8 mm objective equals ×180; and ×18 ocular and 8 mm objective equals ×500), higher objectives being impracticable on account of their short working distances. This equipment is adequate for working upon blood or yeast, but is wholly inadequate for bacteriological work, except that of the simplest character and under conditions quite different from those found in ketchup and other food products.

The counting apparatus or chamber recommended is known as the Thoma-Zeiss haemacytometer, named from the designer and maker. The apparatus consists of a heavy glass slip, on which is cemented a glass 0.2 mm thick, having a circular hole in the middle. In the center of the hole is mounted a smaller disk 0.1 mm thick, leaving an annular space. In the middle of the small inner disk are etched two sets of twenty-one parallel lines which cut each other at right angles. The drop of liquid to be examined is placed on this square, after which it is covered with a specially heavy cover-glass, which, if perfect and adjusted so closely that Newton’s rings appear, gives a layer of liquid 0.1 mm in depth. The drop to be examined must be so small that it remains in the middle of the chamber, but in contact with the cover-glass and bottom of the cell. Each side of the ruled square is 0.1 mm, and as there are 20 spaces on a side, there is a total of 400 small squares, the depth being 0.1 mm, thus the cubical content of each is 1-4,000 c mm or 1-4,000,000 cc. For convenience in counting, every fifth space is sub-divided. Other counting chambers have been devised based on the same principle, but varying chiefly in their rulings for convenience in counting.

The other apparatus recommended consists of a 50 cc graduated cylinder, slides, and cover-glasses.