I worked part time at a McDonald's from ~1991-1995. At the beginning of that period, we immediately assembled Big Macs with freshly grilled patties, then let th

I worked part time at a McDonald's from ~1991-1995. At the beginning of that period, we immediately assembled Big Macs with freshly grilled patties, then let them sit in a warmer for <=10 minutes before throwing them out. By the end of my tenure at McDonald's, we were cooking patties and storing them in steam warmers for up to 30 minutes before tossing them. The same patties were used for regular burgers and Big Macs. We'd create Big Macs as needed by demand, assembling them later. I don't know the #s, but was told that this change was to reduce product waste. Grilling equipment and process also changed over this time period, slightly reducing the number of staff needed to run the grill and reduce the likelihood of overcooked (and thus wasted) meat. I imagine numerous other efficiencies/changes have been made over the decades that would influence the cost to make Big Macs.