This may help you identify 'Speu'
Spew (Spue) is a solidified fat or fatty acid, when the fat liquor introduced during the re-tanning process is destabilised and rises to the surface of the leather creating a white haze or film on the surface. The conditions under which the spew forms (temperature, humidity, changes in temperature, etc.) can be a clue to which type is active on your leather. This will look dry but have a greasy/fatty feel to it. If it is cleaned off it will almost certainly return as it requires a stabilising product to re balance the fats.