Salt crust is the name given to the method of covering of an ingredient, commonly fish such as see bass and grouper, in a sand-like mixture of usually egg-whites and salt. The salt acts as insulation cook the food in an even and gentle manner and after baking, the golden-brown shell is cracked, resulting in moist and evenly cooked food.
Food and Techniques
Traditionally fish is seen most commonly using the salt crust method to be baked but in recent times with salt becoming much cheaper and available than the past, has seen a rise in use in other areas. Usually temperatures of approximately 2000C are used in baking of the salt encrusted fish with the fish being flavoured and seasoned before being covered in the mixture of egg whites and salt. The head and tail are left uncovered and is baked until the crust is golden brown. To serve, the crust is broken and the moistness should be preserved. Vegetables such as celeriac and beetroot are now being seen being baked in a salt crust as well. For beetroot, the stem and roots are cut off and then wrapped tightly in baking paper then covered in a salt crust completely sealed. Another non-traditional method is seen in the version of a pie with ramekins being used and a salt crust to cover the top. 
The technique of salt crust cooking mirrors many cultures: Indian clay-pot cooking, French “en papillote” style and Oriental techniques which involve wrapping food in leaves or bark of a plant. They all aim to lock in moisture and maximise the effect of the seasoning. Covering the ingredient in salt crust is the first part and the second part is baking it. Baking typically occurs in an oven and the fuel is supplied by wood, coal, gas, or electricity. The crust also acts as a mini-oven, locking the heat inside as salt is a poor conductor of heat creating an oven within an oven. This slows heat transfer to the food creating a slow and low dry oven, beneficial to most proteins.
It is said that Egyptians were the first civilisation to utilise salt as a preservative in meat and fish. The earliest Chinese records show that the technique of preserving fish in salt goes back to 2000 B.C. whilst salted fish and bird meat was discovered in aboriginal Egyptian graves. The salt-crusted fish has appeared in many different countries such as the French, Italy, Spain and China. A huge amount of salt is needed to prepare the dish and as such even a few hundred years ago it was very expensive due to salt being a rare commodity in that time period. Earlier than that, the dish would have been reserved only for the wealthy and the prosperous. 
The first recorded reference in China resembling the technique of baking in a salt crust is Salt-Baked Chicken from Dong Jing in the province of Guangdong during the Qing Dynasty (1644-1911). The chicken was cooked and preserved in the salt fields of the area giving them added flavour. In a Muslim cookbook originating from the thirteenth century a layer of salt is placed on a new terracotta tile as a base and the fish is placed on top and another layer of salt is added on, then finally being placed in an oven. However, the earliest recipe found for salt-baked first comes from the fourth century BCE in Archestratus' Life of Luxury. The recipe details for a whole, round white fish such as sea bass, snapper or sea bream that was cleaned then gutted. The fish is seasoned with thyme being inserted into the cavity of the fish prior to the salt crust encapsulating it in two pounds of salt glued together with water and egg whites. Without earlier documentation, the Ancient Greeks seem to be the first ones to pioneer this technique 
Salt is vital for life and is even more so for some Thai communities as it has provided a source of income for generations. The locals are proud of their salt producing heritage hence, there is a salt festival to commemorate and celebrate their history. The Art of Salt Festival lasts for three days offering attractions of sculptures, educational displays where birds, people and other animals are crafted out of salt. A popular dish is the salt crusted fish, stuffed with lemongrass and the salt crust protects the fish from drying out while its being grilled. In Japan salt is even considered sacred as they believe salt is cleansing and is often a defining flavour of Japanese dishes. It plays a major role in the making of dried fish and in the pickling of vegetables.  Turkey is also another important meat which old villages utilised the salt crust to not only to hold in all the juices but also so that the crust could be sealed and marked preventing tampering. Chicken baked in a salt crust is a known traditional dish to the province of Hatay with records showing it was done as early in the Ottoman period. It is regarded that the Chinese applying the technique on the fowl has been transferred and adopted to Anatolia through migrations.
A study conducted by the University of Sinop, Turkey was done to determine the difference a salt crust makes on the rainbow trout (Oncorhynchus mykiss). The rainbow trout was prepared by first being gutted without being scaled with the head and tail being intact. Slices of onion and lemon, parsley and bay leaf were inserted into an incision of the fish’s body and was covered with aluminium foil. This was done to prevent the absorption of salt into the actual flesh of the rainbow trout. The salt crust was made by a combination of rock salt, egg whites and water. The covered fish was baked at 180C for 45 minutes or until golden brown.
The results show that moisture and carbohydrate levels decreased while all the other values increased. Analysis from a statistical viewpoint shows that the salt and carbohydrate values were not found to be significantly different (P>0.05) however the other values were found to be significantly different (P>0.05). Sensory testing was however not done but the flavour of the fish baked in a salt crust was tested by trained panellists. It was concluded that the fish was sufficient in terms of sensory characteristics and some even consumed the dish with added salt. 
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