Sodium nitrite is a direct and fast acting cure agent. It starts reacting with meat structure immediately, converting to nitrous acid and/or nitric oxide. When applied to ground meat the cure happens very fast as the meat particles are very small, so about 12 hours at refrigeration temperature is all that is really needed for a cure in ground sausage meat. Hot smoking the sausage in temperature at or above 140*F will further reduce nitrite. In sausage the USDA sets the in going nitrite level at 156ppm. At this level it is safe to consume with no reduction, although that is impossible because the nitrite reduction starts immediately. For safety concerns it is best to reduce nitrite levels as much as possible in the final product because if the meat is exposed to high heat, like frying in a pan, nitrosamines can form and are thought to be a carcinogen. Careful curing procedure should be used for nitrite reduction for this reason, that’s where cure accelerators come in.
Sodium Erythorbate is chemically the sodium salt of erythorbic acid which is a derivative of ascorbic acid (vitamin C) when used in combination with sodium nitrite it accelerates the nitrite reduction or curing process. Curing times can be reduced by as much as 1/3. So in the case of sausage that can cure in about 12 hours at refrigeration temperature, total cure time is cut by about 4 hours. It still takes 8 hours to obtain a full cure. However if you want to stuff and go straight to the smoker you can, just like using ECA, this is because of the antioxidant value of vitamin C and it’s derivatives that inhibit the formation of nitrosamines. As long as the in going nitrite was 156ppm or less, the sausage is safe to consume. The idea of mixing, stuffing and straight to smoker includes all the time it takes from the moment the nitrite touches the meat to the time it takes for the sausage to reach an internal temperature of about 140*. In all that time curing is taking place. Difference may just be the residual levels of nitrite left in the sausage, that though is offset by the antioxidants in sodium erythorbate so again the product is safe.
Best sausage or general curing practice is to allow the meats to cure properly, the additional sodium erythorbate helps the curing process, depletes oxygen which helps to inhibit oxidation and fixes the cured color, and helps stop fat rancidity.