The genus Lactarius can be difficult to ID to species as many look very similar, as a result microscopic work is often needed to confirm which species you actually have and this species is no exception.    All species of Lactarius release a liquid substance which is referred to as lactating, this substance can be watery, white through to blood red, some of the ‘white milk’ species turn yellow when it combines with oxygen.  The different colours of liquid can also help with identification, this species has a white, unchanging liquid.  The fact that L. subdulcis often associates with Beech trees and has dull flesh-brown colours does also help with ID but so can other, similar looking species such as, L. decipiens (white milk changing yellow) and L. tabidus (white unchanging milk), therefore, in this case, the microscopic details, especially of the spores and of the cells of the cap cuticle are of importance.