I purchased several bottles of Old Grand Dad (86 proof) with ND stamps on the "large" cap (bottles stamped with 86 on the bottom) and love it. Everything I have read says Beam uses the same mashbill and yeast strain as National Distillers. My problem is that they don't taste anything alike and I have tried several different bottles of each. The Beam product seems to me to taste more like JB White (funky "yeast" taste) than the ND OGD. My question is why the difference. Do they really use the old mashbill and yeast? Are they aged the same? and/or Does sitting on a shelf for 25 years affect the taste of the bourbon?

And in that "strain" of thought: How do distilleries that use more than one yeast strain prevent cross contamination?