The Federal Circuit’s decision in Enviro Tech Chemical Services, Inc. v. Safe Foods Corp., Case No. 24-2160 (Fed. Cir May 4, 2026), adds another important chapter to the growing body of indefiniteness law applying Nautilus to “terms of approximation” such as “about,” “approximately,” and “substantially.” In a precedential opinion authored by Judge Lourie, the court affirmed invalidation of patent claims directed to poultry-processing methods because the patent failed to provide objective guidance regarding the permissible variance associated with the claimed pH range of “about 7.6 to about 10.”
The decision is notable because the Federal Circuit did not hold that the word “about” is inherently indefinite. To the contrary, the panel reaffirmed decades of precedent recognizing that approximation language can be appropriate in patent claims. The problem for Enviro Tech was that its specification and prosecution history pointed in multiple directions, leaving a skilled artisan without reasonable certainty regarding the claim boundaries.
For patent prosecutors and litigators, the opinion provides a practical warning: when a numerical range becomes important for patentability over prior art, vague approximation language may not survive scrutiny unless the intrinsic record clearly defines the permissible tolerance.
Charles Gideon Korrell notes that the case is particularly important for chemical, pharmaceutical, and biotechnology patents, where words like “about” are frequently used to accommodate experimental variability and manufacturing tolerances.
The Technology and Claimed Invention
Enviro Tech’s U.S. Patent No. 10,912,321 concerned methods for treating poultry carcasses with peracetic acid during processing. The patent purported to improve poultry weight retention during processing by adjusting the pH of the antimicrobial solution to a more alkaline range.
Representative claim 1 required adjusting the pH of the peracetic acid-containing water “to a pH of about 7.6 to about 10 by adding an alkaline source.”
Safe Foods challenged the claims as indefinite under 35 U.S.C. § 112(b), arguing that the terms “about” and “an antimicrobial amount” failed to provide reasonable certainty regarding claim scope. The district court agreed as to both terms and invalidated the asserted claims.
On appeal, the Federal Circuit affirmed based solely on the indefiniteness of “about,” declining to reach the separate issue concerning “antimicrobial amount.”
The Federal Circuit’s Indefiniteness Framework
The panel began with the familiar Nautilus standard, explaining that claims are indefinite if, when read in light of the specification and prosecution history, they fail to inform skilled artisans “with reasonable certainty” about the scope of the invention.
The court relied heavily on prior Federal Circuit decisions addressing words of approximation, including:
- Ortho-McNeil Pharm., Inc. v. Caraco Pharm. Lab’ys, Ltd.
- Pall Corp. v. Micron Separations, Inc.
- Amgen, Inc. v. Chugai Pharmaceutical Co.
- Interval Licensing LLC v. AOL, Inc.
- Berkheimer v. HP Inc.
Those cases collectively establish that terms like “about” are not automatically valid or invalid. Instead, the acceptability of approximation language depends on whether the intrinsic and extrinsic evidence provide objective guidance regarding the range of acceptable deviation.
The Federal Circuit emphasized that the permissible scope of “about” depends on the “technological facts of the particular case.”
That principle has existed for decades, but Enviro Tech demonstrates that courts are increasingly willing to scrutinize whether the patent actually provides workable boundaries.
The Claims Provided No Objective Guidance
The panel first examined the claim language itself. Claim 1 required a pH “of about 7.6 to about 10,” but the claims never explained how far below 7.6 or above 10 the solution could deviate while still falling within the claim scope.
Both parties agreed that “about” meant “approximately,” but the court concluded that substituting one vague term for another solved nothing. The opinion quoted Interval Licensing for the proposition that a claim remains indefinite if a skilled artisan cannot translate the language into “meaningfully precise claim scope.”
This portion of the opinion reflects a broader post-Nautilus trend. Courts increasingly require objective anchors for subjective or approximation language. Merely invoking industry understanding or ordinary meaning is often insufficient unless the patent itself provides workable standards.
The Specification Hurt More Than It Helped
The specification proved especially damaging to Enviro Tech because it contained inconsistent examples regarding acceptable pH deviations.
Many examples suggested that deviations of 0.3 pH units or less were acceptable. In several experiments, Enviro Tech adjusted the pH when the measured value differed from the target by more than 0.3.
But the specification also included important exceptions. Some experiments continued despite deviations greater than 0.3.
One particularly significant experiment involved processing 5.8 million chickens in a commercial poultry-processing plant while tolerating deviations between 0.35 and 0.5 pH units.
The Federal Circuit considered that example highly informative because the patent’s objective was commercial-scale poultry processing. The large-scale industrial example therefore undermined any argument that 0.3 represented a meaningful boundary.
The court ultimately concluded that the specification’s “conflicting guidance” failed to provide reasonable certainty regarding the meaning of “about.”
Charles Gideon Korrell believes this aspect of the opinion is particularly important because it illustrates a recurring drafting problem: patentees often include numerous experimental examples without considering whether those examples establish conflicting implicit claim boundaries.
In some circumstances, more examples improve enablement and written description support. But in Enviro Tech, the additional examples effectively created internal contradictions about the permissible tolerance range.
The Prosecution History Was Equally Problematic
The prosecution history also undermined Enviro Tech’s position.
The Federal Circuit observed that Enviro Tech treated “about” inconsistently during prosecution. In one argument distinguishing prior art, Enviro Tech referred to “pH 7.6” without using “about.” Yet in another argument on the next page, it referred to “about 8 to about 9.”
The court concluded that the applicant never explained what “about” meant and treated the term inconsistently throughout prosecution.
Relying on Infinity Computer Products v. Oki Data Americas, the panel explained that inconsistent prosecution statements can contribute to indefiniteness when the claims and specification already leave uncertainty unresolved.
Enviro Tech attempted to salvage the claims by arguing that its amendment from “about 7.3” to “about 7.6” implicitly established a 0.3-unit permissible variance.
The court rejected that theory because the amendment was not accompanied by any explanatory remarks defining the scope of “about.”
That discussion underscores another important prosecution lesson: if approximation language matters to patentability, practitioners should consider explicitly defining the intended tolerance during prosecution rather than relying on inference.
The Prior Art Proximity Mattered
Perhaps the most striking part of the opinion appears near the end, where the court explained that the proximity of the prior art heightened the need for precision.
The panel noted that the prior art disclosed pH values as close as 7.0, while the claims were amended to require “about 7.6.”
The court then delivered the opinion’s key takeaway:
“The prior art is almost ‘about’ a pH of 7.6.”
That sentence will likely appear in future indefiniteness briefing for years.
The Federal Circuit effectively recognized a practical relationship between indefiniteness and patentability. When an applicant narrows a numerical range to avoid close prior art, approximation language cannot remain untethered and vague. The narrower the distinction over the prior art, the greater the need for objective claim boundaries.
Charles Gideon Korrell notes that this reasoning may become increasingly important in crowded technology areas where patentability often turns on relatively small numerical differences.
Relationship to Other Recent Federal Circuit Decisions
The decision fits within a broader trend of Federal Circuit scrutiny toward subjective and flexible claim language.
The court’s reasoning closely resembles recent cases requiring objective standards for terms of degree, including:
- Interval Licensing LLC v. AOL, Inc.
- Berkheimer v. HP Inc.
- Infinity Computer Products v. Oki Data Americas
- Akamai Technologies, Inc. v. MediaPointe, Inc. (2025)
What distinguishes Enviro Tech is the court’s detailed focus on internal inconsistencies within the specification itself. The patent did not fail because it lacked examples. It failed because the examples suggested multiple competing answers.
That creates a difficult drafting tension for patent prosecutors. Rich experimental disclosures can strengthen enablement and written description support, but they can also unintentionally create ambiguity regarding claim scope.
Practical Drafting Lessons
The decision offers several practical lessons for prosecutors and litigators:
1. Define Approximation Terms Explicitly
If “about” is intended to permit a particular tolerance range, the specification should say so directly.
2. Avoid Conflicting Experimental Standards
Examples should consistently reflect the intended claim boundary. Multiple tolerance conventions may later be characterized as evidence of indefiniteness.
3. Be Careful When Narrowing Around Prior Art
Approximation language becomes more vulnerable when claims are amended to avoid closely neighboring prior art.
4. Create a Clear Prosecution Record
If approximation language matters, prosecution remarks should explain the intended scope and permissible variance.
5. Consider Whether “About” Is Necessary
In some situations, practitioners may be better served by reciting explicit tolerance ranges or measurement error margins instead of relying on open-ended approximation terms.
Charles Gideon Korrell believes the opinion may encourage prosecutors to rely more heavily on expressly defined tolerances rather than generic modifiers like “about” or “approximately,” particularly in chemical and life sciences applications.
Conclusion
Enviro Tech v. Safe Foods reinforces that approximation language survives only when the intrinsic record provides objective guidance regarding claim scope. The Federal Circuit did not reject “about” categorically. Instead, it held that the patent’s claims, specification, and prosecution history collectively failed to establish a reasonably certain boundary.
The decision also highlights a recurring post-Nautilus theme: ambiguity created during drafting and prosecution can become fatal when a patent later relies on flexible language to distinguish close prior art.
For patent practitioners, the case serves as a reminder that words of approximation require careful support, consistent treatment, and clear objective boundaries. Otherwise, the effort to preserve flexibility may ultimately destroy enforceability altogether.
Here is my coverage of the Nautilus case.
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