Enviro Tech Chemical Services, Inc. v. Safe Foods Corp.

Case: 24-2160   Document: 48     Page: 1   Filed: 05/04/2026




   United States Court of Appeals
       for the Federal Circuit
                 ______________________

     ENVIRO TECH CHEMICAL SERVICES, INC.,
               Plaintiff-Appellant

                            v.

                 SAFE FOODS CORP.,
                   Defendant-Appellee
                 ______________________

                       2024-2160
                 ______________________

    Appeal from the United States District Court for the
 Eastern District of Arkansas in No. 4:21-cv-00601-LPR,
 Judge Lee P. Rudofsky.
                  ______________________

                  Decided: May 4, 2026
                 ______________________

     SETH R. OGDEN, Patterson Intellectual Property Law,
 P.C., Nashville, TN, argued for plaintiff-appellant. Also
 represented by RYAN D. LEVY, NATHAN I. NORTH; KAEL K.
 BOWLING, MARSHALL NEY, Friday, Eldredge & Clark, LLP,
 Rogers, AR.

    DEBRA JANECE MCCOMAS, Haynes and Boone, LLP,
 Dallas, TX, argued for defendant-appellee. Also repre-
 sented by ANGELA M. OLIVER, Washington, DC; AMIR H.
 ALAVI, SCOTT W. CLARK, STEVEN THOMAS JUGLE, Alavi &
 Anaipakos PLLC, Houston, TX.
                 ______________________
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 2   ENVIRO TECH CHEMICAL SERVICES, INC. v. SAFE FOODS CORP.




         Before LOURIE and PROST, Circuit Judges, and
                 BURROUGHS, District Judge. 1
 LOURIE, Circuit Judge.
     Enviro Tech Chemical Services, Inc. (“Enviro Tech”)
 appeals from a decision of the U.S. District Court for the
 Eastern District of Arkansas determining that the asserted
 claims 1–3, 5–12, 14–19, 21–24, 26–29, and 31–33 of its
 U.S. Patent 10,912,321 (“the ’321 patent”) were invalid as
 indefinite. Enviro Tech Chem. Servs., Inc. v. Safe Foods
 Corp., No. 4:21-cv-00601-LPR, 

2022 WL 17721179

 (E.D.
 Ark. Dec. 15, 2022) (“Decision”). For the following reasons,
 we affirm.
                        BACKGROUND
     Enviro Tech’s ’321 patent is directed to “[m]ethods for
 treating poultry during processing for increasing the
 weight of the poultry,” using “peracetic acid.” ’321 patent
 at Abstract. Independent claim 1 is representative of the
 asserted claims and recites:
     1. A method of treating at least a portion of a poul-
     try carcass with peracetic acid, said method com-
     prising the steps of:
     providing, in a reservoir, a peracetic acid-contain-
     ing 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-con-
     taining water, determining the pH of the peracetic
     acid-containing water, and altering the pH of the



     1    Honorable Allison D. Burroughs, District Judge,
 United States District Court for the District of Massachu-
 setts, sitting by designation.
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 ENVIRO TECH CHEMICAL SERVICES, INC. v. SAFE FOODS CORP.    3



    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, plac-
    ing 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 hav-
    ing at least the portion of the poultry carcass
    therein, removing at least the portion of the poultry
    carcass from the peracetic acid-containing water.
 

Id.

 col. 61 ll. 31–58 (emphases added).
     Enviro Tech sued Safe Foods Corp. (“Safe Foods”), as-
 serting that Safe Foods infringed claims 1–3, 5–12, 14–19,
 21–24, 26–29, and 31–33 of its ’321 patent. See J.A. 106.
 During claim construction, Safe Foods alleged that two
 terms of claim 1—“an antimicrobial amount” and “about”—
 were indefinite. See Decision, 

2022 WL 17721179

, at *12.
 The district court determined that both terms were indefi-
 nite and issued a judgment that the asserted claims were
 invalid. Id. at *16, *18; J.A. 11–12.
     Enviro Tech timely appealed. We have jurisdiction un-
 der 

28 U.S.C. § 1295

(a)(1).
                        DISCUSSION
     Patent claims must “particularly point[] out and dis-
 tinctly claim[]” the invention. 35 U.S.C § 112(b). “A claim
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 4   ENVIRO TECH CHEMICAL SERVICES, INC. v. SAFE FOODS CORP.




 fails to satisfy this statutory requirement and is thus inva-
 lid for indefiniteness if its language, when read in light of
 the specification and the prosecution history, ‘fail[s] to in-
 form, with reasonable certainty, those skilled in the art
 about the scope of the invention.’” Interval Licensing LLC
 v. AOL, Inc., 

766 F.3d 1364

, 1369–70 (Fed. Cir. 2014) (al-
 teration in original) (quoting Nautilus, Inc. v. Biosig In-
 struments, Inc., 

572 U.S. 898, 901

 (2014)). “We review
 indefiniteness determinations de novo except for necessary
 subsidiary fact findings, which we review for clear error.”
 Berkheimer v. HP Inc., 

881 F.3d 1360, 1363

 (Fed. Cir.
 2018).
     Enviro Tech challenges both of the district court’s in-
 definiteness determinations. Because we are affirming the
 district court that “about” is indefinite, which renders all of
 the asserted claims invalid, we do not address the alterna-
 tive ground that “antimicrobial amount” is indefinite.
     The district court determined that the intrinsic evi-
 dence––i.e., the claims, specification, and prosecution his-
 tory––did not inform a skilled artisan as to the scope of the
 term “about” with reasonable certainty, and thus that the
 asserted claims were indefinite.         Decision, 

2022 WL 17721179

, at *13–15. We agree.
     We have long held that words like “about” and “approx-
 imately” may be appropriately used to “avoid[] a strict nu-
 merical boundary to the specified parameter.” Ortho-
 McNeil Pharm., Inc. v. Caraco Pharm. Lab’ys, Ltd.,
 

476 F.3d 1321, 1326

 (Fed. Cir. 2007) (quoting Pall Corp. v.
 Micron Separations, Inc., 

66 F.3d 1211, 1217

 (Fed. Cir.
 1995)); see also Interval Licensing, 766 F.3d at 1370–71.
 Terms of degree, like “about” and “approximately,” are not
 inherently definite or indefinite. See Berkheimer, 

881 F.3d at 1364

; see also Amgen, Inc. v. Chugai Pharm. Co.,
 

927 F.2d 1200, 1218

 (Fed. Cir. 1991) (claim term “about”
 may be acceptable in appropriate situations). When a word
 of approximation is used, however, the parameter’s range
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 ENVIRO TECH CHEMICAL SERVICES, INC. v. SAFE FOODS CORP.     5



 must be reasonably certain based on the “technological
 facts of the particular case.” Ortho-McNeil, 

476 F.3d at 1326

 (quoting Pall, 

66 F.3d at 1217

); Amgen, 

927 F.2d at 1218

 (holding “about 160,000 IU/AU” indefinite when
 “nothing in the specification, prosecution history, or prior
 art provides any indication as to what range . . . is cov-
 ered”); see also Interval Licensing, 

766 F.3d at 1371

. We
 consider the claims, patent specification, and prosecution
 history, as well as extrinsic evidence, to ascertain the range
 that is covered.
     We start with the claim language. Claim 1 states that
 the acidity of the peracetic acid-containing water will be
 altered to a “pH of about 7.6 to about 10 by adding an alka-
 line source.” ’321 patent, col. 61 ll. 41–42, 52–53. But the
 claims do 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. The parties agree that
 the ordinary meaning of “about” is “approximately,” but
 “approximately” provides no more guidance on the permis-
 sible deviation of the claimed range than the word “about”
 such that the claim language would inform a skilled arti-
 san as to the meaning of the term. See Interval Licensing,
 

766 F.3d at 1371

 (“Even if a claim term’s definition can be
 reduced to words, the claim is still indefinite if a person of
 ordinary skill in the art cannot translate the definition into
 meaningfully precise claim scope.” (internal quotation
 marks and citation omitted)).
      We turn next to the ’321 patent specification, which
 similarly does not inform a skilled artisan of the scope of
 “about” with reasonable certainty. The specification recites
 numerous experiments conducted by Enviro Tech, wherein
 it would set a target pH, measure the pH, then proceed
 with the experiment depending on how large the difference
 was between the two. In a majority of the experiments,
 Enviro Tech proceeded only when the difference of the ac-
 tual pH was less than or equal to 0.3 of the target pH. See,
 e.g., ’321 patent, col. 39 ll. 22–35, col. 44 ll. 1–8. If the
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 6   ENVIRO TECH CHEMICAL SERVICES, INC. v. SAFE FOODS CORP.




 difference was greater than 0.3, Enviro Tech would most
 often alter the pH to be closer to the target before proceed-
 ing. See, e.g., 

id.

 col. 44 ll. 1–8.
     But there were exceptions to that general practice: In
 several examples, Enviro Tech decided to continue an ex-
 periment even when the pH deviated from the target by
 more than 0.3. See 

id.

 col. 42 ll. 3–8, col. 55 ll. 56–63, col.
 58 l. 50–col. 59 l. 25, col. 59 ll. 32–60. In one such experi-
 ment, conducted with 5,800,000 chickens in “a major U.S.
 processor of poultry,” Enviro Tech proceeded with devia-
 tions between 0.35 and 0.5 of the target pH. 

Id.

 col. 58 l.
 19–col. 60 l. 46. That experiment is particularly informa-
 tive because it involved the largest number of chickens and
 occurred in a processing plant, given that one goal of the
 patented invention is to “increase . . . a processing plant’s
 percent yield.” 

Id.

 at Abstract (emphasis added). And it
 indicates that the 0.3 variance in some examples was not a
 firm indicator of the meaning of “about.” The ’321 patent
 specification’s conflicting guidance thus does not allow a
 skilled artisan to determine the scope of “about” with rea-
 sonable certainty. Cf. Interval Licensing, 

766 F.3d at 1372

 (explaining that a specification that “is at best muddled”
 provides for a “hazy relationship between the claims and
 the written description” and therefore “fails to provide the
 clarity that . . . subjective claim language needs”).
      We then turn to the ’321 patent’s prosecution history.
 Enviro Tech’s treatment of the word “about” during the pa-
 tent’s prosecution was inconsistent and also fails to inform
 a skilled artisan of claim 1’s scope with reasonable cer-
 tainty. For example, in one office action response, Enviro
 Tech argued that “a peracetic acid solution at the lower end
 of the claimed range, pH 7.6,” would not have been obvious
 over the prior art, notably failing to include the term
 “about” in its arguments. J.A. 658. Yet on the next page
 of its response, with respect to another claim, Enviro Tech
 argued that “a step of adjusting the pH to the range of
 about 8 to about 9” would not have been obvious over the
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 ENVIRO TECH CHEMICAL SERVICES, INC. v. SAFE FOODS CORP.    7



 same prior art, including “about” in its arguments.
 J.A. 659 (emphases added).
     At no point in the entire prosecution history does En-
 viro Tech explain what “about” means. Rather, Enviro
 Tech treated the term inconsistently, suggesting that it
 was material to some claims and immaterial to others. See
 Infinity Comput. Prods., Inc. v. Oki Data Ams., Inc., 

987 F.3d 1053, 1059

 (Fed. Cir. 2021) (“Indefiniteness may re-
 sult from inconsistent prosecution history statements
 where the claim language and specification on their own
 leave an uncertainty that, if unresolved, would produce in-
 definiteness.”).
     Enviro Tech argues that the district court should have
 considered the fact that it surrendered claim scope during
 prosecution of the ’321 patent. Open. Br. at 25. According
 to Enviro Tech, the fact that it amended the lower bound-
 ary of its claimed range from a pH of “about 7.3” to “about
 7.6” demonstrates that it disclaimed any pH deviation
 greater than 0.3 pH, and therefore that “about” means less
 than or equal to 0.3. 

Id.

 at 25–26. We are not convinced.
 Enviro Tech points to no remarks it made to the examiner
 that are the sort of “repeated and consistent remarks dur-
 ing prosecution [that] can define a claim term,” nor is En-
 viro Tech’s “amendment accompanied by explanatory
 remarks” suggesting that “about” should be construed to
 mean less than or equal to 0.3 pH. See Personalized Media
 Commc’ns, LLC v. Apple Inc., 

952 F.3d 1336, 1345

 (Fed.
 Cir. 2020). Indeed, Enviro Tech never offered an argument
 to the examiner indicating what “about” means.
     An important determinant in our decision here is the
 very fact that what is now claim 1 was amended in respect
 to pH to avoid prior art, which was as close as a pH of 7.0.
 See J.A. 572. When the specification recites pHs of 6–10,
 see ’321 patent, col. 6 ll. 30–39, col. 39 ll. 12–16, and the
 prior art pH of 7.0 required the claims to be amended, the
 definiteness requirement of § 112 necessitates much more
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 8   ENVIRO TECH CHEMICAL SERVICES, INC. v. SAFE FOODS CORP.




 clarity than using the vague term “about.” The prior art is
 almost “about” a pH of 7.6.
     For the foregoing reasons, the term “about” as used in
 representative claim 1 of the ’321 patent is indefinite, ren-
 dering the asserted claims of the ’321 patent invalid.
                        CONCLUSION
     We have considered Enviro Tech’s remaining argu-
 ments with respect to the term “about” but find them un-
 persuasive. For the foregoing reasons, we affirm.
                        AFFIRMED