As the fixed oil has no pungency or mustard taste, it adds nothing to the flavor of the flour, but, instead, injures its keeping qualities, and, if left in, makes the seed very difficult to be pulverized. It is used as a salad and there is a ready market for it, as there is a great demand for it by the Jewish people.
Since hydraulic presses are expensive, costing from $2,000 to $4,000 each, but a small number of the spice millers press their own mustard seed. They either buy the mustard cake, which has been prepared by special mustard mills, or buy the pure or adulterated flour, already prepared for the market.
Some spice millers are suspicious of the cake, fearing it may be adulterated or be made up of partially poor seed, or of the refuse of previous workings, and they have good reasons for their fears, as such adulteration might occur, but as the pure article is to be judged by the flavor and pungency it may possess, it is as easy to test the cake as the seed.
Mustard is not only very popular as a condiment but is a medicinal rubefacient, as it has many stimulating properties. The use of mustard plasters every household is familiar with; mustard also promotes digestion, and it is a splendid emetic in case of poisoning. A good story is told of a quack doctor who advertised electric belts for sale. He had received many testimonials from those who had bought them, his patrons speaking very highly of the benefit they had received from their use, but as the belts became worn and were ripped open it was found that the electricity they contained was made up of mustard flour.
In the ground mustard or mustard meal, as has been explained, we have only the interior of the seed, with the exception of the few small portions of the husk, which may have escaped in the operation of bolting. The presence of these fragments enables us to recognize the source from which the flour is derived, and also to detect the use of mustard hulls as an adulterant of other food materials.
The farina or black and white mustard differs but little in appearance. The brown, however, is slightly darker. The outer colorous epidermis consists of angular plates, or hexagonal tabular cells, with a center of different brilliancy. It swells up and becomes slimy in water, and, therefore, must be observed in glycerine. At the best it requires some manipulation to see it well, and it is far less prominent in the black seed.
The next coat, denominated the subepidermal, is not prominent and can only be seen at all easily in the white seed.
The third layer is an important one, and in it is found the coloring matter of the brown seed. Its absence is the cause of the lack of color in the white variety. By this layer one is able to tell whether the flour is a mixture of both the black and white seed or if it is derived from one only. Fragments of this layer are common in powdered mustard. It is distinguished by the thick or colorless brown cell walls and their irregular dotted appearance. Between the third and second layers are numerous cells containing some color in the brown seed, but of little importance. Within these comes the important layer, denominated the inner tunic or plasma layer. It separates readily from the other parts of the husk and is often found by itself in the powdered mustard. As its contents are broken up by water or chloral-hydrate, it is necessary to use glycerine or oil in mounting.
The cells and their contents of this layer are large and much alike in both the black and white seed. The interior of the mustard seed is made up of small, soft parenchyma cells, containing the oil and the other constituents of the mustard, but without any trace of starch—a fact which makes adulterations easily detected.
The peculiar pungency and odor of the black seed are due to an essential or fixed oil, myronic acid, which is developed by the action of cold water (hot water will not answer) on two peculiar chemical substances which it contains, which form a compound, termed by the discoverers myronate of potash, but since called synanthrin, an acid with formula C10H19NS2O10. This acid is converted into the volatile oil of mustard or sulphocyanide of allyl C4H5NS, or