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

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
______________________
S ETH R. O GDEN, Patterson Intellectual Property Law,
P.C., Nashville, TN, argued for plaintiff-appellant. Also
represented by RYAN D. L EVY , N ATHAN I. NORTH ; K AEL K.
BOWLING, MARSHALL N EY , Friday, Eldredge & Clark, LLP,
Rogers, AR.
D EBRA J ANECE M CCOMAS , Haynes and Boone, LLP,
Dallas, TX, argued for defendant-appellee. Also repre-
sented by ANGELA M. O LIVER , Washington, DC; AMIR H.
ALAVI, SCOTT W. CLARK, STEVEN T HOMAS J UGLE, Alavi &
Anaipakos PLLC, Houston, TX.
______________________
Case: 24-2160 Document: 48 Page: 1 Filed: 05/04/2026

-- 1 of 8 --

ENVIRO TECH CHEMICAL SERVICES, INC. v. SAFE FOODS CORP. 2
Before L OURIE and P ROST , Circuit Judges, and
BURROUGHS , District Judge.1
L OURIE, 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.
Case: 24-2160 Document: 48 Page: 2 Filed: 05/04/2026

-- 2 of 8 --

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).
D ISCUSSION
Patent claims must “particularly point[] out and dis-
tinctly claim[]” the invention. 35 U.S.C § 112(b). “A claim
Case: 24-2160 Document: 48 Page: 3 Filed: 05/04/2026

-- 3 of 8 --

ENVIRO TECH CHEMICAL SERVICES, INC. v. SAFE FOODS CORP. 4
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
Case: 24-2160 Document: 48 Page: 4 Filed: 05/04/2026

-- 4 of 8 --

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
Case: 24-2160 Document: 48 Page: 5 Filed: 05/04/2026

-- 5 of 8 --

ENVIRO TECH CHEMICAL SERVICES, INC. v. SAFE FOODS CORP. 6
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
Case: 24-2160 Document: 48 Page: 6 Filed: 05/04/2026

-- 6 of 8 --

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
Case: 24-2160 Document: 48 Page: 7 Filed: 05/04/2026

-- 7 of 8 --

ENVIRO TECH CHEMICAL SERVICES, INC. v. SAFE FOODS CORP. 8
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
Case: 24-2160 Document: 48 Page: 8 Filed: 05/04/2026

-- 8 of 8 --