How is corn used in making corned beef? It's not! The closest that the beef comes to corn is that which the cow may have eaten. "Corn" is an old English term used for the word grain. As per AmazingRibs.com, it was used in the phrase of that era "A corn of salt" so it became synonymous with salt. So, what is happening is the meat is being cured with salt. At that time they didn't have the luxury of refrigeration and so the corning process was used to preserve meats.
Now, not the regular salt we use everyday at the dinner table, but curing salt. The curing salts are either Prague #1 or #2 also know as Insta Cure. Prague #1 is more commonly used for the "corning" process. It should be noted, NEVER use any curing salts at the dinner table and do not mistake them for pink Himalayan salt. If used for anything other than curing, they will be hazardous to your health.
What part of the cow is used to make corned beef? The brisket. Other parts of the cow can be used but none is as delicious as the brisket. When you are celebrating St. Patty's Day, chowing down corned beef, it is brisket. Most BBQ'ers know what the brisket is but for those that don't the brisket is the pectoral muscle (chest) of the cow. When it is not corned but smoked, the smoking process can take up to 10 hours since this is an over worked muscle and is very tough. When it is corned the salt breaks down the muscle fibers and transforms the brisket into a piece of tender meat. Oh, have you heard of pastrami? Well, it is a corned brisket that has been lightly smoked and seasoned with liberal amounts of pepper and coriander.
So, when seated at the St. Patty's Day dinner table, exhibit your worldly knowledge and see how many know the origins of corned beef. Most probably will say "who cares" but you know!