When honey supers are taken from the hive for extraction, each frame should be fully capped on both sides of the comb. This signifies to the beekeeper, that the moisture content of the honey has been reduced to the correct level conducive to a product, which will not ferment.
In a perfect world each frame would be covered with sealed cells from one side to the other. Unfortunately nature has its imperfections, and there may be parts of the frame, which are still in the process of being filled, and therefore cells that the bees have not yet capped. The beekeeper must then make his own assessment of the moisture content of these cells before extracting.
This can be done by holding the frames horizontally over the uncapping tray, and giving them a sharp shake. If no honey falls out, then the moisture content is adequate for extraction, but if drops of honey fall easily from the cells, then the frame should be returned to the hive for the bees to complete them.