Section 2144.04(IV)(C) of the Manual of Patent Examining Procedure describes legal precedents relating to “Changes in [the] Sequence of Adding Ingredients” and cites to In re Burhans for the proposition that “the selection of any order of performing process steps is prima facie obvious in the absence of new or unexpected results.” In re Burhans, 154 F.2d 690, 69 USPQ 330 (CCPA 1946).

However, the Patent Trial and Appeal Board (“Board”) recently clarified that the Burhans rule only applies when evidence exists that the process steps in question are already known and used in the cited prior art.