The finished pulp made from skins and cores is not the same as that from whole stock. It contains more fiber, remains more or less lumpy, and lacks the smooth body of whole pulp. The color is not so good, and the flavor is likely to be somewhat different. The flavor of the seed cells and that of the fleshy portion of the tomato are different. Pulp made from each part separately shows marked difference, that from the seed cells being poor in color, but with the more characteristic fruit flavor. Tests show that neither part has any true jellying powers, but that the part from the seed cells gives the quality of smoothness, the holding together of the particles of solids. Neither gives a first class pulp alone.
Home-made ketchup generally has a rather dark reddish or brownish color, due to prolonged heating, made necessary under kitchen conditions. At one time this was thought desirable and some of the older recipes call for the use of caramel in order to imitate this color. Most manufacturers now aim to secure a clean, clear color, preferably bright red. This may be obtained when good fruit is used and handled quickly; a muddy brownish or yellowish color is looked upon with suspicion as indicating poor material or defective methods.
The necessity for a clear red variety has already been pointed out, for without proper stock, a superior product of uniform quality can not be made. The tomatoes must be well vine-ripened, as the presence of green fruit and green butts has a decidedly dulling effect. Colorimeter tests show that the use of even small quantities of green material have an immediate dulling effect. Promptness in handling the fruit after the tissue is once exposed to the air is also essential. The tomato, like some other fruits, turns brownish when the surface is cut or exposed. This does not occur as rapidly, nor is it so marked as in apples or in pears, but it is present. When the tomato is converted into pulp, every particle is exposed to the air for a very short time—long enough to make some slight change. The change is most marked in pulp from raw stock and least in that which has been well heated. It naturally follows that ketchup made promptly from whole stock will have the best color, that from canned tomatoes next, then canned pulp, and lastly, that from trimming stock. Pulp allowed to stand hot for too long a time will have a brownish color like stack burning. When barrel pulp was used, this was ascribed to the tannin extracted from the oak.