lines 372–377: What contrast is in the final paragraph? How does the contrast between what the author sees and what he smells relate to his purpose?

Text:
Grainger had brought a dozen small glass bottles from the lab.
After he opened each bottle, I dipped a fragrance testing filter into it.
The filters were long white strips of paper designed to absorb aroma
chemicals without producing off-notes. Before placing the strips of
paper before my nose, I closed my eyes. Then I inhaled deeply, and
one food after another was conjured from the glass bottles. I smelled
fresh cherries, black olives, sautéed onions, and shrimp. Grainger’s
most remarkable creation took me by surprise. After closing my eyes,
I suddenly smelled a grilled hamburger. The aroma was uncanny,
almost miraculous. It smelled like someone in the room was flipping
burgers on a hot grill. But when I opened my eyes, there was just a
narrow strip of white paper and a smiling flavorist.