I have a brisket flat in my freezer, and I'd love to make corned beef. It would be my first time. When I searched the internet for preparation ideas, I found preparation instructions that called for kosher salt, sea salt, pickling salt, pink salt ( Prague Powder # 1-not Hymalayian) for the brine. I'm a bit hesitant to keep a 5-6 pound brisket in my fridge, as some suggest, 8-10 days in a sea/kosher salt brine. Wouldn't the meat go rancid? Do I need curing salt, such as Prague Powder # 1? How much should you use per pound if the Prague Powder is necessary? It sounds a bit intimidating.
This is probably the 5th time I have said this on this site but make sure the meat is completely thawed. Brine is the process of using a saline solution to dehydrate and hydrate protein molecules. This has the effect of increasing moisture retention of the protein molecules. This just leads to more juicy meat. Often done to tenderise tough cuts of beef or very lean poultry. This process cannot happen if the protein molecules are frozen solid. Putting frozen meat in water could have some safety concerns as well.
As for the curing salts, it is optional. Sodium Nitrates is the active ingredient in Saltpeter. Something humanity has used for many centuries. It is just a more potent and reliable version of a naturally occurring mineral. What it gives to the brine is rose pink color and a very pleasant Smokey flavour, but a 6 - 8 % salt solution will preserve the meat exactly the same with or without the nitrates. In the case of brines you add nitrates for flavour and color not for any additional preservation effect.
Curing salts are coloured pink so that they are not confused with regular salt. Some care should be applied when dealing with it. Even just consuming a tiny bit can be dangerous. Keep it away from children and pets and mark all containers clearly. It is very potent.
As for salts for brines you really need a fine salt. For curing whole cuts of meats coarse salt is what you need. I dislike using finishing salts for curing. I just find they have to many added minerals. This is not a problem when used as a table salt, but for curing it just complicates things unnecessarily. I also dislike using salt with iodine or anti caking agent. Anti caking agent leaves a very unpleasant sediment in your brine. Will not kill you but can lead to some off flavours. For a brine I would just use as pure a fine sodium chloride as you can find.
A 1kg pack of sodium nitrates is probably be enough to cure anywhere between 1 to 3 metric tons of meat. For a 2 - 3 kg brisket I would use between 1 - 2 grams in a 5 liters of water.
It is also worth noting the difference between the two types of Prague powder. Any nitrates labelled type 1 is sufficient for most applications. Prague powder type 2 is specifically formulated for products that cure for many months, like cured sausages. They have a preservation effect that last a lot longer.
As the nitrates are done for taste in a brine you can find a dose that has the correct smokey flavour for you. In any other types of curing like cured sausage, for example, you use the curing salts exactly as the recipe demands.
As for regular sodium chloride it is important to weigh the salt. Different brands of salt vary greatly in volume and you need to be precise with this. As a general rule 6 - 8 % salt by weight per liter of water. This means 60 - 80 grams of salt per liter of brine. If we are using a 5 liter brine that means 300 - 400 grams of salt in the 5 liters.
Lastly, you mentioned corning your brisket. If you want to corn beef then you have to use pickling spice. A Texas brisket is often brined but it only becomes corned beef if pickling spice is used in the preparation.