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.
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.
The salt used is of the grade known as dairy salt.
A variety of spices is used in the manufacture of ketchup. Among these are cinnamon, cassia, cloves, all-spice, pepper, cayenne pepper, ginger, mustard and paprika. Spices may be used either in the form of whole spices, ground spices or volatile spice oils. Whole spices are thought by some to produce a better flavor. Ground spices, when used, should be secured from a reputable manufacturer, as there is a possibility of adulteration or use of low-grade material in ground products. Volatile spice oils are used to some extent, especially of spices containing large amounts of tannin, where there is liability of discoloration due to the formation of iron tannate during the manufacture of the ketchup. Acetic acid extracts of spices are also used to a limited extent.
The sugar may be added at any time during the making of the ketchup, but is preferably added during the latter part of the cooking. There is less danger of scorching if added at this time. It should be added gradually and scattered over the surface of the cooking ketchup so that it may go into solution more readily.
Vinegar is always added a few minutes before finishing. The acetic acid of the vinegar is volatile, and a large portion of it will be driven off with steam if added at the beginning of the cooking.
Salt may be added at any time during the cooking, but it is best to add it sufficiently soon so that it will be dissolved and thoroughly mixed with the product.
The onions should be added chopped at the beginning of the cook.
Spices, either whole or ground, are generally placed in a bag and added at the beginning of the cook. If the volatile oils are used, they should be added shortly before finishing the ketchup, as otherwise a large amount of them may be carried off with the steam.
Ketchup of uniform color, consistency and taste can be produced only by controlling the quality and quantity of its constituents. Therefore, any satisfactory method of control necessitates the determination of the solids in the batch of cyclone juice before sugar, salt, vinegar and spices are added. Control, based solely on uniform specific gravity of the finished product, assures only that the specific gravity is uniform; it does not assure uniformity in consistency, sweetness, acidity, or in any other characteristic of the product.
Since, under any specific procedure in a factory, the distinctive tomato flavor and the consistency of the finished product depend entirely on the tomato solids, and since about half the final acidity and sugar content is derived from the same source, the control of the tomato solid content is especially important.
Fortunately the solids in cyclone juice have a fairly uniform composition. The ratio of total solids to insoluble solids is fairly constant, likewise the ratio of sugar to acid. The sugar in cyclone juice varies from about 42 per cent to 54 per cent of the total solids, averaging about 50 per cent.
As the consistency or body of ketchup is due chiefly to the tomato solids, the amount of evaporation necessary to secure ketchup of the desired consistency from a known volume of pulp measured at the boiling temperature and of known Brix or specific gravity can be determined from Table 9, page 56. For instance, if the volume of the boiling pulp is 800 gallons and the corrected Brix reading of the filtrate is 5.10, it is found from Table 9 that it will be necessary to evaporate to 423 gallons to secure a ketchup of approximately the consistency of 1.040 pulp, to 374 gallons for a consistency comparable to 1.045 pulp and to 334 gallons for a consistency comparable to 1.050 pulp. This evaporation is carried out, of course, with the addition of the necessary ingredients for the making of ketchup. The amount of these ingredients can be varied in order to secure ketchup of the desired flavor.
After having once decided on the amount of ingredients to be used, the manufacture may be standardized. Supposing for instance on evaporating 800 gallons of partly concentrated pulp of Brix of filtrate (5.10) to approximately 334 gallons (calculated from the 1.050 column in Table 9) it has been found that the use of 301 pounds of sugar, 26.7 gallons of 100 grain vinegar, 66.8 pounds of salt and 50.2 pounds of onions together with spices gives ketchup of the flavor desired. Dividing the amount of each ingredient by 334, it is found that each gallon of finished ketchup contains .9 pound of added sugar, .2 pound of salt, .15 pound of onions, and about 10 ounces of vinegar. After having determined the amount of each ingredient per gallon of finished ketchup, it is easy to make a table giving the amount of ingredients necessary for a given volume of cyclone juice or concentrated pulp of any gravity. In Table 11 such calculations are made. This table is based on securing a ketchup having the consistency of 1.050 pulp and starting with 800 gallons of boiling pulp of specific gravity 1.0220 (Brix reading of filtrate 5.10). Some manufacturers may desire to base the amount of ingredients on 100 gallons or multiple of 100 gallons of finished ketchup. This may be done by first making out a table similar to 9 and then calculating the amount of pulp and other ingredients for 100 gallons of ketchup. This would, however, involve considerable work as unless the pulp used had a constant specific gravity, a calculation of the quantity of each ingredient would have to be made for the volume of pulp for each batch.
Table 11.—Manufacture of Ketchup. Quantity of Constituents to be Added to 800 Gallons of Boiling, Partly Concentrated Pulp
| Specific gravity of pulp at 68° F. |
Filtrate from pulp | Volume of finished ketchup |
Added constituents | ||||
| Degrees Brix at 68° F. |
Specific gravity at 68° F. |
Sugar | 100-grain vinegar |
Salt | Onions | ||
| _Gals._ | _Lbs._ | _Gals._ | _Lbs._ | _Lbs._ | |||
| 1.0154 | 3.50 | 1.0137 | 226.0 | 203 | 18.1 | 45.2 | 33.0 |
| 1.0158 | 3.60 | 1.0141 | 232.0 | 209 | 18.5 | 46.4 | 34.8 |
| 1.0162 | 3.70 | 1.0145 | 239.0 | 215 | 19.1 | 47.8 | 35.9 |
| 1.0166 | 3.80 | 1.0149 | 245.0 | 221 | 19.6 | 49.0 | 36.8 |
| 1.0170 | 3.90 | 1.0153 | 252.0 | 227 | 20.2 | 50.2 | 37.8 |
| 1.0174 | 4.00 | 1.0157 | 258.0 | 232 | 20.6 | 51.8 | 38.7 |
| 1.0178 | 4.10 | 1.0161 | 265.0 | 239 | 21.2 | 53.0 | 39.8 |
| 1.0182 | 4.20 | 1.0165 | 272.0 | 245 | 21.7 | 54.4 | 40.8 |
| 1.0186 | 4.30 | 1.0169 | 278.0 | 250 | 22.2 | 55.6 | 41.7 |
| 1.0190 | 4.40 | 1.0173 | 285.0 | 257 | 22.8 | 57.0 | 42.8 |
| 1.0194 | 4.50 | 1.0177 | 292.0 | 263 | 23.4 | 58.4 | 43.8 |
| 1.0199 | 4.60 | 1.0181 | 299.0 | 269 | 23.9 | 59.8 | 44.9 |
| 1.0202 | 4.70 | 1.0185 | 306.0 | 275 | 24.5 | 61.2 | 45.9 |
| 1.0206 | 4.80 | 1.0189 | 313.0 | 282 | 25.0 | 62.6 | 47.0 |
| 1.0211 | 4.90 | 1.0193 | 320.0 | 288 | 25.6 | 64.0 | 48.0 |
| 1.0216 | 5.00 | 1.0197 | 327.0 | 294 | 26.2 | 65.4 | 49.1 |
| 1.0220 | 5.10 | 1.0201 | 334.0 | 301 | 26.7 | 66.8 | 50.2 |
| 1.0224 | 5.20 | 1.0205 | 341.0 | 307 | 27.3 | 68.2 | 51.2 |
| 1.0228 | 5.30 | 1.0209 | 347.0 | 312 | 27.8 | 69.4 | 52.1 |
| 1.0232 | 5.40 | 1.0213 | 354.0 | 319 | 28.3 | 70.8 | 53.2 |
| 1.0236 | 5.50 | 1.0217 | 361.0 | 324 | 28.9 | 72.2 | 54.2 |
| 1.0240 | 5.60 | 1.0221 | 368.0 | 331 | 29.4 | 73.6 | 55.2 |
| 1.0244 | 5.70 | 1.0225 | 374.0 | 337 | 29.9 | 74.8 | 56.2 |
| 1.0249 | 5.80 | 1.0229 | 381.0 | 343 | 30.5 | 76.2 | 57.2 |
| 1.0253 | 5.90 | 1.0233 | 388.0 | 349 | 31.0 | 77.6 | 58.2 |
| 1.0257 | 6.00 | 1.0237 | 395.0 | 356 | 31.6 | 79.0 | 59.3 |
| 1.0261 | 6.10 | 1.0241 | 402.0 | 362 | 32.1 | 80.4 | 60.4 |
| 1.0266 | 6.20 | 1.0245 | 409.0 | 368 | 32.7 | 81.8 | 61.4 |
| 1.0271 | 6.30 | 1.0249 | 416.0 | 374 | 33.3 | 83.2 | 62.5 |
| 1.0275 | 6.40 | 1.0253 | 422.0 | 380 | 33.8 | 84.4 | 63.4 |
| 1.0279 | 6.50 | 1.0257 | 429.0 | 386 | 34.3 | 85.8 | 64.4 |
| 1.0283 | 6.60 | 1.0261 | 436.0 | 392 | 34.9 | 87.2 | 65.4 |
| 1.0287 | 6.70 | 1.0265 | 443.0 | 399 | 35.4 | 88.6 | 66.5 |
| 1.0291 | 6.80 | 1.0270 | 450.0 | 405 | 36.0 | 90.0 | 67.5 |
| 1.0295 | 6.90 | 1.0274 | 457.0 | 411 | 36.6 | 91.4 | 68.6 |
| 1.0299 | 7.00 | 1.0278 | 464.0 | 418 | 37.1 | 92.8 | 69.6 |
| 1.0304 | 7.10 | 1.0282 | 471.0 | 424 | 37.7 | 94.2 | 70.7 |
| 1.0309 | 7.20 | 1.0286 | 478.0 | 430 | 38.2 | 95.7 | 71.8 |
| 1.0313 | 7.30 | 1.0290 | 485.0 | 437 | 38.8 | 97.1 | 72.8 |
| 1.0318 | 7.40 | 1.0294 | 492.0 | 443 | 39.4 | 98.5 | 73.8 |
| 1.0322 | 7.50 | 1.0298 | 499.0 | 449 | 39.9 | 99.9 | 74.9 |
| 1.0326 | 7.60 | 1.0302 | 506.0 | 455 | 40.5 | 101.3 | 76.0 |
| 1.0330 | 7.70 | 1.0306 | 513.0 | 462 | 41.1 | 102.7 | 77.0 |
| 1.0335 | 7.80 | 1.0310 | 521.0 | 469 | 41.7 | 104.2 | 78.2 |
| 1.0339 | 7.90 | 1.0315 | 529.0 | 476 | 42.3 | 105.8 | 79.4 |
| 1.0343 | 8.00 | 1.0319 | 536.0 | 482 | 42.9 | 107.2 | 80.4 |
| 1.0347 | 8.10 | 1.0323 | 543.0 | 489 | 43.5 | 108.6 | 81.5 |
| 1.0352 | 8.20 | 1.0327 | 550.0 | 495 | 44.0 | 110.0 | 82.6 |
| 1.0356 | 8.30 | 1.0331 | 557.0 | 501 | 44.5 | 111.4 | 83.6 |
| 1.0361 | 8.40 | 1.0335 | 564.0 | 508 | 45.1 | 112.8 | 84.7 |
| 1.0365 | 8.50 | 1.0339 | 571.0 | 514 | 45.7 | 114.2 | 85.7 |
| 1.0369 | 8.60 | 1.0343 | 578.0 | 520 | 46.2 | 115.6 | 86.8 |
| 1.0374 | 8.70 | 1.0348 | 585.0 | 527 | 46.8 | 117.0 | 87.8 |
| 1.0379 | 8.80 | 1.0352 | 592.0 | 533 | 47.4 | 118.4 | 88.8 |
| 1.0383 | 8.90 | 1.0356 | 600.0 | 540 | 48.0 | 119.0 | 90.0 |
The use of Table 11 gives a ketchup of medium concentration. Using this as a basis the manufacturer can decide the extent to which he should evaporate to secure a ketchup of the consistency desired and modify the table accordingly.
Final concentration of the ketchup is controlled in the same manner as for pulp, either by a gauged tank or by specific gravity determination. If we start, therefore, with a given volume of partially concentrated cyclone juice and determine the solids present, we can in every case quickly ascertain from the appropriate table the number of gallons of finished product we should obtain, and the gauge stick or attached gauge glass will indicate when to stop evaporation in the tank. One advantage of measuring the original volume at the boiling temperature is that no temperature corrections are necessary, as both the initial and final temperature measurements are approximately the same.
The final concentration may be controlled, as stated above, by determining the specific gravity of the finished product by one of the methods given under pulp (see page 33 and following). The determination of specific gravity at this point will probably give more accurate results than the use of a gauge stick, and is to be recommended for use with the finished product, provided the added constituents have been standardized. The method described on page 42 for determining the specific gravity of hot tomato pulp, may be used for obtaining the per cent of solids in the boiling cyclone juice in place of the Brix spindle reading on the filtrate.
Table 11 for controlling the concentration of finished ketchup is based on the idea that there shall be a definite volume of partly concentrated pulp in the tank when the inflow of cyclone juice is stopped and the sample is taken for analysis. In this respect, this method of controlling the concentration of ketchup varies from the method described on page 54 for the control of the concentration of tomato pulp. It is sometimes convenient to secure this definite volume by filling the tank to a greater height than is desired and evaporating until the desired volume is secured. When this point is reached the sample of pulp is taken for specific gravity and steam is again turned on the tank.
The Abbé refractometer may also be used for controlling the final concentration of the ketchup. This provides a very simple and quick method for determining the percentage of solids. It requires but a few drops of the filtered liquor from the ketchup to make the determination. The reading may be taken and the calculation made in one or two minutes’ time by use of Tables 13 and 14.
The table for calculating the solids from the refractometer reading is Geerlig’s table for dry substance in sugar-house products, and is taken from the Methods of the Association of Official Agricultural Chemists, 1919. The entire table is not given but only the range over which it might possibly be desired to use it in the control of the manufacture of ketchup.
The results by this method are only approximate, but are sufficiently accurate for manufacturing control. Table 12 gives a comparison of the solids obtained by drying in vacuum at 70° C. with results obtained by the refractometer.
Table 12.—Solids in Ketchup Obtained by Drying in Vacuum at 70° C. and by Abbé Refractometer from Geerlig’s Table
| Solids in tomato ketchup | |
| By drying in vacuum at 70° C. |
By Abbé refractometer |
| Per cent | Per cent |
| 29.5 | 29.0 |
| 30.0 | 29.4 |
| 32.8 | 32.4 |
| 28.0 | 27.9 |
| 22.0 | 21.8 |
| 27.7 | 28.0 |
There are several errors in this determination which partially compensate for each other and give results fairly comparable with those obtained by drying. The refractometer of course determines only soluble constituents. Since salt gives a higher refractive reading than the same per cent of sugar, and since tomato solids give a higher refractive reading than the same percentage of sugar, and since any acetic acid of the vinegar is also read as solids on the refractometer, the total increase in reading due to these different factors nearly compensates for the insoluble solids of the ketchup.
The variation of the per cent of solids as obtained by the refractometer from that obtained by drying will depend somewhat on the composition of the ketchup and in using the refractometer it is advisable to also determine the solids by drying on a few samples to obtain the relation between the two figures for that particular ketchup.
Table 13.—Refractive Index and Per Cent Solids in Tomato Ketchup [21]
| Refractive index |
Per cent solids |
Decimals to be added for fractional readings |
| 1.3484 | 11 | 0.0001 = 0.05 |
| 1.3500 | 12 | 0.0002 = 0.1 |
| 1.3516 | 13 | 0.0003 = 0.2 |
| 1.3530 | 14 | 0.0004 = 0.25 |
| 1.3546 | 15 | 0.0005 = 0.3 |
| 1.3562 | 16 | 0.0006 = 0.4 |
| 1.3578 | 17 | 0.0007 = 0.45 |
| 1.3594 | 18 | 0.0008 = 0.5 |
| 1.3611 | 19 | 0.0009 = 0.6 |
| 1.3627 | 20 | 0.0010 = 0.65 |
| 1.3644 | 21 | 0.0011 = 0.7 |
| 1.3661 | 22 | 0.0012 = 0.75 |
| 1.3678 | 23 | 0.0013 = 0.8 |
| 1.3695 | 24 | 0.0014 = 0.85 |
| 1.3712 | 25 | 0.0015 = 0.9 |
| 1.3729 | 26 | 0.0016 = 0.95 |
| 1.3746 | 27 | 0.0001 = 0.05 |
| 1.3764 | 28 | 0.0002 = 0.1 |
| 1.3782 | 29 | 0.0003 = 0.15 |
| 1.3800 | 30 | 0.0004 = 0.2 |
| 1.3818 | 31 | 0.0005 = 0.25 |
| 1.3836 | 32 | 0.0006 = 0.3 |
| 1.3854 | 33 | 0.0007 = 0.35 |
| 1.3872 | 34 | 0.0008 = 0.4 |
| 1.3890 | 35 | 0.0009 = 0.45 |
| 1.3909 | 36 | 0.0010 = 0.5 |
| 1.3928 | 37 | 0.0011 = 0.55 |
| 1.3947 | 38 | 0.0012 = 0.6 |
| 1.3966 | 39 | 0.0013 = 0.65 |
| 1.3984 | 40 | 0.0014 = 0.7 |
| 1.4003 | 41 | 0.0015 = 0.75 |
| 0.0016 = 0.8 | ||
| 0.0017 = 0.85 | ||
| 0.0018 = 0.9 | ||
| 0.0019 = 0.95 | ||
| 0.0020 = 1.0 | ||
| 0.0021 = 1.0 |
In using Table 13, find the refractive index which is next lower than the reading actually obtained and note the corresponding whole number for the per cent of dry substance. Subtract the refractive index obtained from the table from the observed reading; the decimal percentages corresponding to this difference, as given in the column so marked, is added to the whole per cent of solids as first obtained.
Correction must also be made for the temperature if above or below 28° C. The temperature correction is obtained from Table 14. For instance, suppose the refractive index was 1.3750 and that the temperature was 25° C. The per cent of solids as obtained from the table would be 27.2. The correction for temperature would amount to .14, which would be added to this reading, giving 27.34 as the per cent of solids.
Table 14.—Corrections for Temperature to be Used with Table 13
| Temperature, ° C. |
Per cent of solids. | |||||
| 10 | 15 | 20 | 25 | 30 | 40 | |
| To be subtracted | ||||||
| 20 | 0.55 | 0.56 | 0.57 | 0.58 | 0.60 | 0.62 |
| 21 | .48 | .49 | .50 | .51 | .52 | .54 |
| 22 | .42 | .42 | .42 | .44 | .45 | .47 |
| 23 | .34 | .35 | .36 | .37 | .38 | .39 |
| 24 | .27 | .28 | .28 | .29 | .30 | .31 |
| 25 | .21 | .21 | .22 | .22 | .23 | .23 |
| 26 | .13 | .14 | .14 | .15 | .15 | .16 |
| 27 | .07 | .07 | .07 | .07 | .08 | .08 |
| To be added | ||||||
| 29 | 0.07 | 0.07 | 0.07 | 0.07 | 0.08 | 0.08 |
| 30 | .13 | .14 | .14 | .14 | .15 | .15 |
| 31 | .21 | .21 | .22 | .22 | .23 | .23 |
| 32 | .27 | .28 | .28 | .29 | .30 | .31 |
| 33 | .34 | .35 | .36 | .37 | .38 | .39 |
| 34 | .42 | .42 | .43 | .44 | .45 | .47 |
| 35 | .48 | .49 | .50 | .51 | .52 | .54 |
Whether or not ketchup should be processed after filling into bottles depends on the conditions under which it is bottled. If the bottled product can be sealed at 180° F. or better a process is not necessary and is an unnecessary expense and waste of time, besides it may injure the color of the product. With the modern type of equipment it is possible to fill the bottles at a temperature which obviates sterilization. Care must be taken that the temperature of the ketchup in the receiving tank feeding the filler does not fall too low. Care must also be avoided in order not to fill the ketchup at too high a temperature as it results in excessive shrinkage of the contents.
For ketchup filled at relatively low temperature a process should be used. The process necessary will depend upon the temperature at which the ketchup is filled and on the time that may elapse between filling and processing. Sanitary conditions of the factory and equipment are exceedingly important not only in relation to ease of sterilization but also in securing a product of good quality.
In stacking ketchup it is best to stack the bottles upside down. This tends to prevent darkening of the ketchup in the neck of bottle, a condition known as “black neck.” It has been our experience that wherever this condition has occurred it is due to leakage of air into the bottles. Stacking bottles in this way undoubtedly keeps the cork of the cap moist and makes the seal more effective.