I assume the grain direction is perpendicular to the pantry cabinets? How thick is the butcher block? I doubt you need to worry about bowing or bending, but you might want to make the post T-shaped, with a cross piece let into the top, parallel to the cabinets. If you do this, be sure that whatever means you use to attach the butcher-block to the cross piece allows for some lateral movement, because a solid wood top will expand and contract with seasonal humidity changes.

Thanks jon1270.

I was going to plane some 8/4 maple stock down, so figure the final counter depth would be about 1 ¾".

IÂm thinking the room will look better if the grain runs parallel to the cabinets  same sightlines as the finished floor. Would centering 3/8" threaded rod (say every 7" OC) provide enough support?

boc_ct

No, threaded rod won't work. At that size, the counter could easily be a quarter-inch longer in the humid summer than in the dry winter months. For threaded rod to contribute any strength it would have to be under tension, with washers and nuts on each end. This restraint would keep the counter from expanding with increases in humidity, so some of the wood fibers would become permanently compressed. When the humidity dropped at the next dry season, the counter would shrink and cracks would open where the wood fibers had been compressed.

Orienting the grain parallel with the cabinets AND have that span unsupported from below is begging for problems. Sorry.

You have to build it flat- select the grain properly so the shrinkage won't cause cupping.
Attach it properly- use tabletop fasteners available at woodcraft or online- these allow the top to float. Screwing it in securely will stress it if it tries to shrink, potentially it will split. Alternative: use oblong holes for the screws to permit movement.
Finish it the same way on the underside- this will prevent it from warping due to uneven drying/wetting.
Casey