DIY Finishing Salt (Maldon, Fleur de Sel)

I boiled 2 cups of regular sea salt to completely dissolve in 1 cup water then put it in a flat tray in the dehydrator on the jerky setting - the next day I did have a load of big crackly crystals and some dust.

A simple way to get "more" out of your salt, is to start with BIG crystals, and coat them gently in oil before sprinkling them over the food. That way they do not melt on contact with the food as they are protected from the water by the film of oil , and add a awesome crunchy texture to the serving.

Technically I think that your question is more chemistry related and not directly cooking related.

I can give you a few hints no what you can do to get crystals, but a chemist should be able to give you a lot better advice.

First, making the salt water solution:

1. Get distilled or at least demineralized water. You do not want to add random minerals that are dissolved in water to your salt :)
2. Make a saturated solution of salt-water at a high temperature ... something like 90-95C (~194-203F). The idea is that at higher temperatures you get more of the salt dissolved in the water more easily.
3. Keep the salt solution at that high temperature (well covered to reduce evaporation) for some time to make sure that any undissolved salt has settled to the bottom. You are interested only in the salt in the solution.
4. Take only the saltwater without any undissolved salt. Until and including this step, the solution should be best keep at the same temperature. If you have to move the solution, at least make sure that the thing that you are moving it into is not cold.

OK, now it is time to make the crystals:

1. Crystals grow. If they grow too fast or are disturbed (thermally or mechanically) they fall apart and end up being smaller. This is why when you make ice cream you churn the ice constantly (mechanical disturbing the formation of possibly ice crystals) or chill it with liquid nitrogen (thermally shocking the crystals and make them break apart). What you get are very small crystals if you disturb them.
2. Crystals grow when they are "forced out of solution" - that is, when the concentration of the salt in water is higher than the solubility of salt in water at that specific conditions. Pressure is one of the factors, but we will just ignore it completely. The factors that you can work with are Temperature and concentration (just remove water from the solution by evaporation)
3. To get BIG crystals, you have to let them grow slowly.
4. So, what you need to do is to cool the solution very slowly AND/OR
5. Evaporate the water out of solution very slowly (take care not to get dust in the solution during this procedure :) )

Unfortunately this is all the advice that I can give you now. Be aware that crystals are delicate and you might need a few attempts until you get the desired result. As a fun fact, there exist conditions where you will actually get a BIG salt Cube aka, a single salt Crystal by doing this :) . Cool indeed , but not very useful for cooking :)

If you live near the sea, you could copy the methods used industrially to make sea salt. Simply collect some sea water and spread it over a wide flattish pan in the sun to evaporate, repeat again and again until a decent layer of salt builds up. To do this you do need to live somewhere hot, with plenty sun, near the sea.

I'm pretty late to the party but I have found that evaporating at temps as high as 140 degrees Fahrenheit will give pretty nice crystals. I am still looking for cheap, easy ways to consistently maintain lower temps, my target from some reading I have done is about 110 degrees Farenheit. I got 140 with the simmer burner on my range heating a water bath and the saline suspended in that. Also going to try the fresh air when summer comes and such temps are there for the asking.