Last week, the U.S. Court of Appeals for the Federal Circuit issued a precedential decision in Enviro Tech Chemical Services, Inc. v. Safe Foods Corp., No. 2024-2160 (May 4, 2026), affirming the district court’s determination that the asserted claims of Enviro Tech’s U.S. Patent No. 10,912,321 were invalid as indefinite because the term “about” failed to inform skilled artisans of the claims’ scope with reasonable certainty.
Enviro Tech’s ’321 patent is directed to methods for treating poultry during processing using peracetic acid. Representative claim 1 recites altering the pH of a peracetic acid-containing water to “a pH of about 7.6 to about 10 by adding an alkaline source.” Enviro Tech sued Safe Foods for infringement, and Safe Foods challenged the claims as indefinite during claim construction. The district court agreed that both “about” and “an antimicrobial amount” were indefinite, rendering all asserted claims invalid. Enviro Tech appealed.
The Federal Circuit affirmed. Because the Court’s indefiniteness finding on “about” disposed of all asserted claims, it did not address the alternative “antimicrobial amount” ground. The Court reiterated that terms of degree like “about” are not inherently definite or indefinite but must be evaluated based on the intrinsic evidence in the particular case.
Turning to the intrinsic record, the Court found each source wanting. The claim language itself provided no guidance on permissible deviation from the recited pH boundaries. The specification was internally inconsistent: while most experiments proceeded only when pH deviated by 0.3 or less from the target, others—including the patent’s largest-scale trial involving 5.8 million chickens at a commercial processing plant—proceeded with deviations between 0.35 and 0.5. The prosecution history likewise offered no clarity, as Enviro Tech used “about” inconsistently—including it in arguments on some claims while omitting it from analogous arguments on others—and never explained its meaning to the examiner. The Court further noted that because the claims had been amended from “about 7.3” to “about 7.6” to avoid prior art at pH 7.0, the prior art was nearly “about” a pH of 7.6, making the absence of a clear boundary particularly problematic.
This decision underscores that patent drafters must ensure terms of degree are anchored by objective guidance in the specification or prosecution history—especially where the claimed range sits close to the prior art.
