I seem to remember reading some work about the ordering of toppings when building a burger or sandwich but this may just be my imagination. If there is any scientific literature or we'll constructed experiments I'd love a link.
But here is my theory and I am curious as to your thoughts. I remember hearing that we taste the ingredients on the top first despite the bulk of our taste buds being on our tounge. I am curious as to whether this is true and if so why? If that is in fact the case, I think those fresh/crisp topping with mild acidity - but not over powering of the burger - should go on top (lettuce, tomatoes, raw onions). My reasoning is two fold, they are more delicate flavours so you want to be able to taste them before reaching th burger and sauces which may over power these ingredients and, secondly, these are mildy acidic and can 'wake up' the palette (or at least that was the justification for the buttermilk sorbet opening to the tasting menu CS did). I also think the top of your mouth, the hard palette, is more sensitive to temperature than your tounge - being bone - and I find chilled ingredients followed by warm ingredients to be a pleasurable sensation so I am think of keeping the tomatoe slices, lettuce and Diced raw onions chiled Until the last moment and placing the lettuce underneath the tomato to insulate it from the heat o the patty. The raw onion dice will go directly on the cheese, however, which will act as a gluey mat. If serving with bacon, I think it should go under the cheese a to be held in place. I will cut the tomato slices thinly so that they do not pull out.
Under the patty, I will put pickles which, while acidic, I feel might fight to compete with the patty if my theory on tasting the top first is true. Underneath, however, they will add a nice textural element and a second dose of cleaning acidity. I will also put the sweet condiments (sauces) on the the bottom andput them on generously. In my debate between a messey burger and a dirty burger, I think the perfect burger should be a naughty, primal event - so messy. More importly, I know sweet receptors are on the tip of the tounge so I was some sweetneess oozing out when you clamp down to bite. Thankfully chewing mechanics move the meat to the back of the mouth where the bitter receptors are located and a good char on the burger will stimulate those senses.
With that in mind, I think I will set up my burger party buffet line with the bottom buns first and following that progression and the top buns at the end of the line so people are surreptitiously forced to build their burger in the most logical order.
