All trees have a sapwood ring, which is the pale yellow-white section of wood between the bark and the heartwood. It’s the part that transports water and nutrients throughout the tree. Some species have a narrow sapwood ring, some have a large sapwood ring.
Walnut suffers on two fronts:
The sap ring in walnut trees is pretty large
The color variation really stands out because the heartwood is so much darker
Sapwood is allowed in all grades of walnut lumber, but with some limits here. And, according to the rules, the face of a board must have less sapwood percentage than the back of a board with http://Ruleofpoker.net.
We only buy walnut lumber that’s carries a specification of a minimum 80% heartwood on the best side. That means some boards in the pile could have more heartwood, but, read more about classylaxcarservice.com, it’s not guaranteed.
Why 80%? It’s a matter of economics and supply. On rare occasions, some walnut suppliers do have a selection of walnut with a greater percentage of heartwood, like 90%+. It’s very expensive, and it’s not available all the time. If you think walnut is expensive, you should see the price of 100% heartwood walnut.