A pulp may be reduced in a vacuum pan in about one-fourth the time necessary in the open kettle and with a marked conservation of color and flavor. The vacuum pan may be used for quick reduction and the finish be made in open kettles in order to apply the heat long enough to spice and to sterilize. There are possibilities along these lines which have not been developed.
The time of cooking a batch of ketchup will depend upon the equipment and the consistency of the finished product. With a good kettle or coil and ample steam-supply a batch should be completed in from thirty-five to forty-five minutes. This gives sufficient time to get the most desirable flavor from the spices and is not so long as to result in discoloration.
The selection of the spices depends entirely upon the flavor desired. Cinnamon, cassia, cloves, allspice, mace, pepper, paprika, cayenne pepper, mustard, ginger, coriander, bay leaves, caraway and celery seed, are all to be found in the various formulae. Some manufacturers spice lightly in order to retain the maximum of the base flavor, while others go to the opposite extreme on the misguided assumption that they will act as preservatives. The quantity used should be determined by the flavor desired and upon no other consideration. The spices may be used whole, ground, or in some cases as acetic acid or oil extracts. The whole spices are preferred by nearly all the manufacturers of high grade goods. They are more expensive, but give a different flavor from the extracts. The spices are weighed for each batch and are tied in a bag or placed in a wire basket and suspended in the kettle while cooking. Some use very large quantities and cook from only ten to twelve minutes in order to get a distinctive flavor. This is very expensive, as only a small quantity of the flavoring matter is extracted in such a short time. One of the serious objections to the use of the whole spices is that they may darken the ketchup and also cause some discoloration in the neck of the bottle. For that reason, black pepper and allspice in particular are being discarded, and oil of cloves is being used in part for the whole berries. The grade of the spice will also have an effect, the cheap stock being unsuitable for a bright clean product. Small quantities of ground cayenne pepper are used as a substitute for the black pepper.