It should be understood that this total acidity will by no means be constant, as there is such a great variation in the natural acidity of tomatoes. Tomato pulp made from tomatoes all grown in the same locality, and condensed to a specific gravity of 1.035, will run as low as 0.40 per cent in natural acidity, and as high as 0.70 per cent. This will cause the total acidity of the catsup to vary accordingly. When in doubt as to whether you are getting the proper acidity, send samples to a chemist and have the acetic acidity determined. This is the acidity of the vinegar alone. It should not run below 0.60 per cent. This figure should be taken as the absolute minimum for acetic acidity. Testing the Finishing Point For testing the finishing point of catsup I recommend either testing by the eye or the hydrometer method as described under the testing of pulp. The eye cannot often be relied upon, although some experienced cooks are very good at judging by the eye, and they do not need a mechanical device of any kind. The specific gravity determination by weight, and cooking to a certain gauge, or for a certain length of time, will not do at all for catsup. I have used the hydrometer method on catsup for a number of years, and it is entirely satisfactory. A little experimenting will indicate the number of degrees on the hydrometer, when immersed in the hot catsup, at which the catsup is heavy enough so that it will be of the right thickness when cold. After this point has been determined every batch should be almost exactly alike if it is cooked to this point. Holding Batches Catsup should not be held in the cooking kettle very long, as the sugar is apt to caramelize where the catsup is in contact with the hot surface of the kettle or coil. Also, the air darkens it somewhat. Of course, if the jacket or coil is completely exhausted, and the valves are absolutely tight, there should not be this burning or caramelization while holding a batch. However, there is often a very slight leak in the valve, and the coil or jacket is thus kept hot constantly. The quicker the cooked batch is let out of the kettle, the better. Making Catsup From Pulp Many catsup makers make their catsup from pulp altogether. They feel that during the season they have their hands full packing pulp, and they can work this pulp up into catsup during the winter months when there would otherwise be little or nothing to do. When pulp is used, about 29 5–gal. cans of specific gravity 1.035 is sufficient for a batch of catsup of 100 gallons. Do not add water to the pulp, even if it is a little heavy. The only danger from not getting a very long cook is that there will not be a very complete extraction of the spices, when whole spices are used in a sack. If, however, each spice bag is cooked in two batches, this danger is greatly minimized.