On May 4, 2026, the United States Court of Appeals for the Federal Circuit (Judges Lourie, Prost, and District Judge Burroughs) affirmed a decision of the United States District Court for the Eastern District of Arkansas holding that asserted claims of U.S. Patent No. 10,912,321 (“the ‘321 patent”) were invalid as indefinite under 35 U.S.C. § 112(b).
Enviro Tech Chem. Servs., Inc. v. Safe Foods Corp., No. 2024-2160 (Fed. Cir. May 4, 2026). The decision addresses the circumstances under which a term of approximation renders a patent claim indefinite, particularly when the specification provides conflicting guidance and the prosecution history reflects inconsistent treatment of the term.
The ’321 patent is directed to methods of treating poultry during processing to increase the weight. Representative claim 1 recites:
1. A method of treating at least a portion of a poultry carcass with peracetic acid, said method comprising the steps of:
providing, in a reservoir, a peracetic acid-containing water, wherein the peracetic acid-containing water comprises water and an antimicrobial amount of a solution of peracetic acid;
after the step of providing the peracetic acid-containing water, determining the pH of the peracetic acid-containing water, and altering the pH of the peracetic acid-containing water to a pH of about 7.6 to about 10 by adding an alkaline source;
after the step of determining the pH and altering the pH of the peracetic acid-containing water, placing into the peracetic acid-containing water at least a portion of a poultry carcass;
after the step of placing at least the portion of the poultry carcass into the peracetic acid-containing water, determining the pH of the peracetic acid containing water in the reservoir with at least the portion of the poultry carcass therein, and altering the pH of the peracetic acid containing water to a pH of about 7.6 to about 10 by adding an alkaline source; and
after the step of determining the pH and altering the pH of the peracetic acid-containing water having at least the portion of the poultry carcass therein, removing at least the portion of the poultry carcass from the peracetic acid-containing water.
During claim construction, defendant argued that both “an antimicrobial amount” and “about” were indefinite. The district court agreed as to both terms and entered a judgment that the asserted claims were invalid.
On appeal, the Federal Circuit affirmed the indefiniteness determination with respect to “about,” noting that, because that finding rendered all asserted claims invalid, it did not need to address the alternative ground that “antimicrobial amount” was also indefinite. The Court reviewed the indefiniteness determination
de novo, applying the standard that “[a] claim fails to satisfy this statutory requirement and is thus invalid for indefiniteness if its language, when read in light of the specification and the prosecution history, ‘fail[s] to inform, with reasonable certainty, those skilled in the art about the scope of the invention.’”
The Court began by noting its established precedent that “words like ‘about’ and ‘approximately’ may be appropriately used to ‘avoid[] a strict numerical boundary to the specified parameter,’” and that “[t]erms of degree, like ‘about’ and ‘approximately,’ are not inherently definite or indefinite.” However, “when a word of approximation is used, … the parameter’s range must be reasonably certain based on the ‘technological facts of the particular case.’”
The Court examined the intrinsic record in sequence.
As to the claim language, the Court found that claim 1 “does not provide any guidance on how much below a pH of 7.6 or above a pH of 10 the peracetic acid-containing water can be to meet the limitation.” And, while the parties agreed that the ordinary meaning of “about” is “approximately,” the Court held that “‘approximately’ provides no more guidance on the permissible deviation of the claimed range than the word ‘about’ such that the claim language would inform a skilled artisan as to the meaning of the term.”
As to the specification, the Court found that it “similarly does not inform a skilled artisan of the scope of ‘about’ with reasonable certainty.” The specification describes experiments conducted by patentee, where patentee set a target pH and continued the experiments depending on the difference between target and actual pH. In numerous experiments continued by patentee, the actual pH deviated by 0.3 or less from the target pH. Therefore, patentee argued that “about” means a deviation of 0.3 or less. But, in several examples, patentee continued experiments with deviations greater than 0.3, including one experiment conducted with 5,800,000 chickens (the largest experiment by number of chickens). This “conflicting guidance” prevents a skilled artisan from determining the scope of ‘about’ with reasonable certainty.
Turning to the prosecution history, the Court found that the use therein of “about” is inconsistent and fails to inform a skilled artisan with reasonable certainty. The Court emphasized that “[a]t no point in the entire prosecution history does patentee explain what ‘about’ means. The Court rejected patentee’s argument that its amendment of the lower boundary of the claimed range from “about 7.3” to “about 7.6” demonstrated that “about” means a deviation of 0.3 or less. The Court found no repeated and consistent use nor explanatory remarks to define the term.
The Court concluded by identifying what it called “[a]n important determinant”: that the specification recites pHs of 6–10 and that claim 1 was amended to avoid prior art as close as a pH of 7.0. In such circumstances, “the definiteness requirement of § 112 necessitates much more clarity than using the vague term ‘about.’” As the Court observed, “[t]he prior art is almost ‘about’ a pH of 7.6.” The implication of this “determinant” is clear: where “about” is used in the context of a claimed boundary that is close to the prior art—and where the amendment creating that boundary was made specifically to distinguish the prior art—then increased precision is required, and the vague term “about” cannot satisfy the definiteness requirement.
This decision is a reminder that drafting patent claims with clarity is essential. Approximation terms like “about” and “approximately” should be approached with caution, especially when the claim scope must be distinguished from close prior art.
