I had a 4R1B last night that was rich, spicy, sweet and smooth with minimal heat and burn at 50% abv. Tonight I am having an OFBB which has nice spice and richness but considerably more heat and burn than the 4R1B at 49% abv. I just assumed the alcohol content had the largest influence on the heat and burn. This tasting suggests I am mistaken and am curious what factors besides alcohol content contribute to the expression of heat and burn in bourbon?