The dry salt method leads to a much quicker penetration of the fish than the brine method, and should always be used in warm weather.
(b) The Freshness of the Fish. The decay processes gather impetus day by day. It is clear, therefore, that in order to avoid the possibility of “souring,” the fish should be salted with the least possible delay.
(c) The Quality of the Salt. (1) Its Purity. The impurities commonly present in Fishery Salt are the sulphates and chlorides of calcium and magnesium.
The following analysis show the composition of typical samples of Fishery Salt.
| Composition. | German Rock Salt. | Italian. | Spanish. | French. | English. |
|---|---|---|---|---|---|
| % | % | % | % | % | |
| Salt (Sodium chloride) | 97·28 | 96·59 | 96·63 | 95·86 | 98·9 |
| Calcium chloride | — | 0·32 | — | 0·16 | — |
| Magnesium chloride | 0·25 | 1·19 | 0·96 | 0·35 | 0·08 |
| Magnesium sulphate | — | 1·75 | 0·73 | — | — |
| Sodium sulphate | 0·44 | — | — | — | 0·04 |
| Sodium bicarbonate | 0·01 | — | — | — | — |
| Insoluble (Calcium sulphate, sand, etc.) | 2·02 | 0·15 | 1·68 | 3·63 | 0·98 |
| 100·00 | 100·00 | 100·00 | 100·00 | 100·00 | |
| Moisture | 0·20 | 6·54 | 4·47 | 1·39 | 3·25 |
The Spanish and Italian salts are solar salts, obtained by evaporating sea-water by the heat of the sun. Solar salt nearly always contains more magnesium salts than brine salt does. This constitutes a serious disadvantage to the fish curer.
Of the calcium salts which occur as impurities in Fishery Salt, the sulphate is practically insoluble in brine, and is probably without action upon the salting process.
Calcium chloride, on the other hand, resembles magnesium chloride and is an undesirable constituent of Fishery Salt, for calcium chloride, and to a lesser extent magnesium chloride and magnesium sulphate, diminish the rate at which the salt penetrates the fish. Curing will, therefore, be delayed, and in warm weather (above 70°F.) this may result in the souring of the fish.
To obtain rapid and thorough curing, therefore, it is necessary—especially in warm weather—to use salt which contains as little calcium and magnesium salts as possible.
Pure salt, used dry, produces a soft, yellow-meated fish which is flexible in the hand. Salt containing calcium chloride or magnesium chloride produces a harder and stiffer fish with a markedly whiter colour.