Kim v. The Earthgrains Co., No. 01 C 3895, Slip Op. (N.D. Ill. Feb. 18, 2010) (Cox, Mag. J.). 

Judge Cox granted defendant summary judgment, limiting plaintiff’s potential damages to the date that the Patent Office issued plaintiff’s reexamination certificate. During reexam, the transitional phrase in each of the claims at issue was revised from "consisting essentially of" to "consisting of." "Consisting essentially of" signals a partially open claim which can include non-claimed ingredients so long as they do not materially affect the claimed properties of the invention. "Consisting of," however, signals a closed claim limiting it to the listed elements, unrelated elements and unavoidable impurities. 

The defendant argued that the changed transitional phrases were substantive changes which limited the damages period to the period from the reexam certificate forward. The Court held that the changed transitional phrases was a substantive change. The plaintiff argued that the changed transitional phrases did not change the scope of her patents based upon plaintiff’s research. But the Court held that the plaintiff had not shown that any element excluded from the original claims would have also been excluded from the reexamined claims. The Court also explained the scope of "consisting essentially of" as follows:

[A] formula which falls under a "consisting essentially of" claim may contain additional "active" ingredients not listed in the claim, as long as the additional active ingredients do not materially alter the "basic and novel" characteristics of the invention. Ecolab also suggests that additional active ingredients which improve the performance of the basic claim formula, but do not otherwise change its function, do not materially alter the "basic and novel" characteristics of the invention.