I have some bottles of mead aging in my cellar since May, and yesterday I noticed a few bottles have an amber-colored sap-like substance on the exterior of the cork (see photo). The substance is highly viscous (like the sap of a pine tree) and lacks any distinguishable smell or taste. The corks are from my LHBS and are the agglomerated type. Any ideas what this could be? I have a theory but I din't want to bias anyone yet.