In a recent workshop with our friend, Rich, we explored not only shio koji in burgers but grain varietal shio koji's in burgers. We were looking to see what the flavor impact would be. We seasoned one burger with a 10% salt brine. The other burgers were seasoned with shio kojis that were all made with 10 percent salt: jasmine rice, brown rice, and barley. We seasoned each burger with 10 percent seasoning so that each burger would end up with 1% final seasoning, before cooking.
We mixed the seasoning into the burgers and put them onto a rack in the refrigerator overnight. The idea was to allow the enzymes in the shio koji to work on the meat and develop amino acids. A secondary benefit we observed was an air dried exterior to the meat. When we cooked the burgers on the grill they did not want to stick to the grates.
As we cooked the meat we observed the burgers with shio koji browned more rapidly and generated a darker coloring than the baseline brined burger. We used the old finger test to judge the burgers done-ness. This was flawed. The addition of the seasonings and the overnight air drying firmed the meat and created a denser meat ring around the interior meat. The burgers felt done, medium rare, but were substantially rarer when we cut into them. (Right here is where I see a great benefit to cooking meats uniformly first in a CVap or even a low oven and then applying the final browning and crusting.)
How did the burgers taste? Really what was unique was the wide range of flavors. The brine burger was seasoned, meaty and juicy. The jasmine shio koji created a sweet flavor to the meat. The brown rice shio koji produced notes of blue cheese. The barley shio koji had intense porcini mushroom flavors. What we also noticed was the meat that was treated with shio koji had a tighter bind to it and was less juicy than the brined burger.
Adding shio koji to a burger, and in that same sense, to any ground meat product, has unique possibilities for flavor development. What also has me just as excited is the use of liquid salt--brines, in burgers and their derivatives.