Enviro Tech Chem. Servs., Inc. v. Safe Foods Corp., Appeal No. 2024-2160 (Fed. Cir. May 4, 2026)

In its only precedential patent opinion last week, the Federal Circuit affirmed a district court’s determination that asserted claims of Enviro Tech’s U.S. Patent No. 10,912,321 were invalid as indefinite.  In so holding, the court clarified when terms of approximation like “about” may fail to apprise a skilled artisan about the scope of a claimed numerical range.

The ’321 patent claims a method for treating a poultry carcass with peracetic acid to increase its weight.  The claims recite placing the carcass into a solution with “an antimicrobial amount” of peracetic acid, checking the pH of the solution before and after the carcass is added, and adding an alkaline source to achieve “a pH of about 7.6 to about 10” at those monitoring points.  While acknowledging that “words like ‘about’ and ‘approximately’ may be appropriately used to avoid a strict numerical boundary” (cleaned up), the Federal Circuit explained they are “not inherently definite or indefinite,” and found that on the facts of this case, the recited approximate pH range failed to reasonably apprise the public about what range was covered.

The reviewing panel explained that when terms of approximation are used, the relevant parameter’s range must still be reasonably certain in view of the intrinsic and extrinsic evidence.  Here, in various experimental embodiments described in the patent’s specification, the applicant inconsistently applied the criteria recited in the claims, often proceeding when the current pH was within 0.3 of the target pH, but proceeding on deviations of between 0.35 and 0.5 in the largest-scale example.  The applicant also applied the “about” qualifier inconsistently during prosecution when distinguishing pH ranges taught by the prior art.

Notably, apart from Enviro Tech’s inconsistent use of the word “about,” the Federal Circuit found that the closeness of the prior art and “the very fact that what is now claim 1 was amended in respect to pH” was “[a]n important determinant in our decision.”  Here, “the definiteness requirement of § 112 necessitates much more clarity” precisely because “[t]he prior art is almost ‘about’ a pH of 7.6.”

Accordingly, the Court affirmed that the asserted claims were indefinite based on the use of “about” in this case, and did not reach the district court’s finding that “an antimicrobial amount” also rendered the claims indefinite.

The opinion can be found here.

By Jason A. Wrubleski

This article summarizes aspects of the law and does not constitute legal advice. For legal advice with regard to your situation, you should contact an attorney.