An air dried salt of a fair degree of purity (about 98 per cent on a moisture-free basis) is perfectly satisfactory for catsup. The purer salts are often desirable in the canning of vegetables where lime and magnesia are apt to have a toughening or hardening effect, but in catsup a very small quantity of lime and magnesia salts have no ill effect.
Salt should be added a few minutes before the vinegar is put in. It is desirable to add the salt toward the end of the cooking, as it acts to some extent on the copper of the coil or kettle. Great care should be used in so adding the salt that it will all dissolve. I have often seen a large mass of undissolved salt in the bottom of a cooking tank after a batch of catsup was let down, even when the salt had been thrown in a half hour before the cooking was completed. The reason for this was that the salt was thrown in without scattering it, and it fell quickly to the bottom of the tank in one mass. Owing to the fact that the circulation below the coil was poor, and that salt does not dissolve readily in boiling water or boiling tomato juice, a large proportion of it remained undissolved.
Salt is less soluble in hot water than in cold water. It should be placed in small containers, such as small pails or boxes, so that it will be light in weight and can easily be scattered over the surface of the boiling pulp. If this is done, and done slowly, there is no need of agitating devices to dissolve the salt. Agitators are also unnecessary to dissolve the sugar if it is added in this way, although sugar dissolves more readily than salt.
Thirty pounds of salt is about the right amount for a 100–gallon batch.
Vinegar
The kind of vinegar usually used in catsup is the strong distilled vinegar—about 100 grain, which contains 10 per cent of acetic acid. The stronger the vinegar, the better, as the weaker vinegars require too much volume to be handled, and dilute the catsup too much when they are added.
Most manufacturers buy their vinegar in barrels. However, some of the larger ones have it shipped in tank cars from which it is pumped at the factory into a large storage tank, and siphoned off as needed. This is the better way when it is used in large enough quantities to warrant buying it in this manner. Barreled vinegar often contains very finely divided charcoal, which is sometimes hard to strain out; the barrels are often full of nails from which the vinegar dissolves iron, and this iron, in combination with the tannic acid of spices, produces a chemical compound (iron tannate) which is as black as ink; and sometimes the barrels contain some foreign liquid, which was left in them when they were filled with vinegar. The use of barrels also requires a lot of handling, and the waste by evaporation through the wood is considerable when the vinegar is held over a long time. One might imagine that the evaporation from a large storage tank would be greater than from barrels. However, such is not the case, as there is much more surface per gallon for evaporation in the barrel than in the large tank. Vinegar shipped in tank cars is free from contamination and is easily and economically handled. Barreled vinegar should always be strained through fine cheesecloth.
Transference of Vinegar
The use of steam pumps and ejectors, in fact any kind of steam appliance for hoisting vinegar, should not be used, as the steam passes into the vinegar, dissolves in it, and dilutes it. If you pump 100–grain vinegar into a storage tank with a steam pump you may find that you have 90–grain when you get it up there. If it is necessary to pump the vinegar, and it usually is, a small electric pump should be used. Either enamel lined or wooden pipe should be used for vinegar. All iron pipe and fittings should be eliminated.