Heavy, sweet, burnt, sometimes a little like caramel.

It is not DEF burn. DEF is the fluid added for NOx reduction, and isn't associated with the particle burn off, they are different systems. The burn is the cleaning or regeneration cycle for the particulate filter.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue