How to Cure a Brisket for Corned Beef & Sous-Vide

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I was recently asked the following question? 

(1) since we all know only salts are absorbed into meat, what's the benefit of curing with a rub that you wash off? (2). Do you really need a 3 week cure on a piece of meet that's about an inch thick - especially if you're then cooking it SV at length?

So why the long curing process? The current understanding and general rule for curing is 1/4 inch per day for absorption; however, the available information does not consider diffusion and nitrite breakdown. But the USDA has mandated that Nitrates and nitrites can be dangerous when consumed in considerable amounts. Therefore, the USDA requires that nitrites be present at < 200 ppm in finished meat products. But here is the elephant in the room. How do we test for this? A mandate with no way of knowing how to comply. 

"The current acceptable daily intake (ADI) for nitrates is 3.7 milligrams per kilogram of body weight per day (mg/kg BW/day). The safe level for nitrites was re-established at 0.07 mg/kg BW/day, close to the slightly more conservative existing ADI of 0.06 mg/kg BW/day."

Over-curing is impossible since this is an EQ cure and not a gradient or box-cure. There are no diminishing consequences with longer curing times, and ultimately, there is an upside. It's tough to calculate the uptake of Cures because all proteins are different. The percentage of fat also plays a role in this as it pertains to the surface and intermuscular, and cures have difficulty penetrating fat. I've used brisket for Pastrami/Cornedbeef and bacon. Although I think two weeks would have been adequate, the extra week allowed the Nitrites to break down even further and for everything to diffuse. 

Now on to the penetration question of the other ingredients. The other surface ingredients, as you know have, don't penetrate all that much. I think Dr. Blonder from Amazing ribs observed they penetrated about one-eighth of an inch (both sides = 1/4 inch) at about a week. Allowing the extra time adds to the flavor profile and helps break down the Nitrites PPM. Having cured many many types of meat and especially Bacon and Corned Beef, there is a difference in flavor profile the longer you go. 

I grew up in NYC and frequented many cured meat shops. I've always asked the proverbial question, HOW LONG? I even went as far as to ask about the curing process. Yeah, they are not giving up that info. Most do Wet-Cures which is way more complicated to calculate the uptake and diffusion. Most had no idea what I was referencing. These shops use recipes handed down over time and never get into the weeds. 

By Law, 3.82 oz of Cure #1 can be used in one gallon of water, but it burns the meat, and the PPM is enormous. Most use somewhere around a 1/4-1/5 of the allowable amount. 

My Bubbe lives across the street from Katz Deli, and I can't tell you how many times I've eaten there. They cure for 3-Weeks always. If it's good enough for them, it's good enough for me. 

Again thanks for the question.