TAKEAWAY: Patent practitioners should take care when drafting an application to ensure that the intended meaning of claim terms is maintained throughout the specification and be aware of possible ramifications of arguments during examination.

Imprecise definitions may have a significant impact on patent claim interpretation. The Federal Circuit case Cultor Corp. v. A.E. Staley 224 F.3d 1328 (Fed. Cir. 2000) illustrates the degree to which a definition of a claim term can inform claim scope.

In Cultor Corp. v. A.E. Staley, patent owner Cultor filed an infringement action against Staley of U.S. Patent Nos. 5,667,593 and 5,645,647, directed to water-soluble polydextrose for use in food products. The ’593 and ‘647 patents disclosed a method for remedying the bitter taste in polydextrose attributed to the use of citric acid in manufacturing. The method involved passing the polydextrose, in aqueous solution, through an ion-exchange resin to remove residual citric acid. Staley’s process utilized phosphoric acid instead of citric acid. Staley argued that phosphoric acid did not produce a bitter taste.

While the claims that Cultor sought to enforce did not expressly recite citric acid, the district court looked to the patent specifications to construe the claims as limited to polydextrose produced using citric acid:

“As used herein, the expression ’water-soluble polydextrose’ (also known as polyglucose or poly-D-glucose) specifically refers to the water-soluble polydextrose prepared by melting and heating dextrose (also known as glucose or D-glucose), preferably with about 5-15% by weight of sorbitol present, in the presence of a catalytic amount (about 0.5 to 3.0 mol %) of citric acid.”

The district court focused on this definition together with arguments made during prosecution distinguishing the claims on the basis of the ability to remove citric acid to grant summary judgment of non-infringement.

On appeal, the Federal Circuit agreed with the district court on claim interpretation and its finding of non-infringement. In a case several years later, the Federal Circuit characterized Cultor Corp. v. A.E. Staley as including a restrictive interpretation “based on an express limiting definition . . . in the specification. . . . As the court explained in Cultor, ’Whether a claim must, in any particular case, be limited to the specific embodiment presented in the specification, depends in each case on the specificity of the description of the invention and on the prosecution history . . . Claims are not correctly construed to cover what was expressly disclaimed.’” Liebel-Flarsheim Co. v. Medrad, Inc., 358 F.3d 898, 907 (2004).

Practitioners should be mindful when including express definitions in a patent application, not only from the perspective of what is encompassed by a term but also what may be implicitly excluded. Since claims can be limited to a specific embodiment presented in the specification, it is good practice to review the claims in light of description provided in the specification.