Experiments on the Spoilage of Tomato Ketchup

by A. W. Bitting

Fig. 2.—Large receiving room showing the sorting belt.

PULPING.

The clean tomatoes should be conveyed to the steaming tanks and subjected to steam heat until the skins burst and the meat softens. After a short heating the tomatoes should be run through a “cyclone” where the skins, seeds, etc., are removed and they are rubbed to a pulp. To remove very small particles and fiber, the pulp may be run through a sieving machine at once; or, if ketchup of the smoothest possible kind is to be made, this procedure should be delayed until after the cooking. The pulp is collected in a receiving vat, and only such an amount should be provided in advance as will keep the kettles full, as it is better to stop the tomatoes before going to the washer than to have the pulp stand for some hours. In common practice, however, the pulp is either sent to the cooker at once, or it is allowed to stand and partially separate. If tall casks are used for this separation the solids will rise to the top and the clear watery portion is drawn off at the bottom, or the pulp may be strained through cloth bags. The object of this separation is to secure greater concentration of the solids, retain a brighter color, and shorten the time of cooking.

COOKING AND SEASONING.

Fig. 3.—A section of a kitchen showing the copper cookers.

The cooking may be done in copper kettles, as shown in figure 3, though these are being superseded by enamel tanks containing silver-plated coils in order to secure the brightest color. By using the latter the discoloration due to the splashing of the contents against the walls of the copper vessel is avoided, and economy of space is secured. Whole or ground spices, or acetic acid or oil extracts of the spices may be added to the pulp in such proportion as the particular brand demands. The spices most used are cloves, cinnamon, mace, and cayenne pepper; but paprika, pepper, mustard, cardamon, coriander, ginger, celery, and allspice are used by some manufacturers. When whole spices are used, it is the practice to suspend them in a cloth bag or a wire basket and to take them out after boiling. They tend to darken the color of the ketchup, a result considered undesirable by some. The ground spices are used sparingly, with the exception of cayenne pepper. The acetic acid extracts of spices are used because they are economical and give a brighter red color than is obtained with the whole spice. The oil extracts produce no discoloration, but they are the most expensive and give an objectionable flavor. Hungarian sweet paprika is now quite largely used and adds to the color as well as to the flavor. Sugar, salt, and vinegar are added in such proportion as may be desired, and in some brands onions and garlic are used.

EVAPORATION AND FINISHING.

The pulp is evaporated rapidly to such consistency as the grade and price will warrant, the reduction in volume being from 40 to 60 per cent. This is accomplished in about forty-five minutes. The cooking is not continued longer than is necessary, as each minute added to the cooking darkens the finished product.