Ingredient file // Vitamin or mineral
Calcium Sulphate
A gelling mineral with a side of calcium
Calcium sulfate is gypsum, a calcium and sulfate mineral, ground to a fine powder. In wet dog food it helps gels and chunks hold their shape and adds a little calcium. It does nothing more for the dog, and nothing worse.
Role in the food Does a job- What it is
- Gypsum, a calcium and sulfate mineral, ground to a fine white powder and used to set gels and add calcium.
- Made from
- Mined gypsum rock or power plant scrubber gypsum
- Main job
- Sets gels, adds calcium
- Typical amount
- About 0.2 to 2% of a gelled pet food
- Watch for
- Purity grade and source, which no label shows
- Not the same as
- Construction plaster or drywall
Our read // In our catalog
In 1 of every 1,540 foods we track
Share of foods that list it
0%
2 of the 3,080 foods with an ingredient list on file, from 1 brand. All wet dog food.
Each square is 1% of the catalog
Where it sits on the label
Median position 6. In the top five of 1 food, so it is usually a main ingredient.
Above the salt
Almost always listed before the salt, so there is more of it than a pinch.
Who leans on it
100%
of the foods that list it are from Now Fresh. 1 brand use it in total.
What it is
How it is made
Gypsum is quarried and mined underground, and coal power plants make a synthetic version when they scrub sulfur from their smoke. Most goes into wallboard and plaster; food additives sit among its smaller uses.1,4,5,9
- 01 // Source Gypsum ore Natural gypsum comes from quarries and underground mines. One mined feed-grade product is at least 92% gypsum.
- 02 // Process Crushed and dried Ore is crushed and screened, then dried to remove surface moisture before grinding.
- 03 // Process Ground, sometimes heated Grinding gives a fine powder. Heating it fully below 300 °C drives off the bound water, giving the anhydrous form.
- 04 // Output Calcium sulfate powder A fine, white to slightly yellow-white odorless powder, about 23% calcium as the dihydrate, mixed into the gel or gravy.
What is in it
Composition, as fed
23
% calcium
Calcium in pure gypsum as it is usually sold, with water bound in the crystal. The rest is sulfate and water, so it is a moderate calcium source.
Why it is in the bag
There to set the gel, with some calcium
- Main nutrition
- Supporting nutrient
- Does a job
- Mostly filler
Wet food makers add it mainly for texture. It dissolves slowly and releases calcium, which sets the gel inside meat chunks as they firm up. FDA lists it as a firming agent, stabilizer and texturizer, and also as a nutrient supplement. One older Spillers patent uses it at 0.2 to 2% of the product. It is about 23% calcium, so how much of the food's calcium it supplies depends on the amount used, which labels do not show.1,4,6
-
01
Sets alginate gels
Calcium turns soluble alginate into an insoluble gel that binds ground meat into chunks. Calcium sulfate dissolves only slightly in water, so the gel sets gradually instead of all at once.3,6
-
02
Adds calcium
At about 23% calcium it counts toward the food's mineral total. FDA lists it as a nutrient supplement in human food, and it also supplies sulfate.1,4
-
03
Firms and stabilizes
FDA allows it in human food as a firming agent, stabilizer, thickener and texturizer, the same jobs it does in puddings and processed vegetables.1
-
04
A bulk feed mineral
Mined feed-grade gypsum is already sold as a calcium and sulfur supplement for livestock feed, and FDA treats it as safe in animal feed under good manufacturing practice.2,5
How much A pet food gelling patent puts this slow-dissolving calcium salt at 0.2 to 2% of the final product, preferably 0.5 to 1%.6
Our read // The claims
What the evidence supports
Strong: controlled studies in dogs agree. Some: small or mixed dog data. Thin: mechanism or lab work only. None: nothing, or the evidence points the other way.
-
Brands say
Holds wet food chunks and gels together
Evidence
- Strong
- Some
- Thin
- None
This is plain chemistry. Calcium cross-links alginate into a gel, and a Spillers patent uses calcium sulfate as the slow-release calcium for meat chunks at 0.2 to 2% of the product. It shapes texture, not nutrition.6
-
Brands say
Adds calcium for strong bones
Evidence
- Strong
- Some
- Thin
- None
It is about 23% calcium. In a cross-over study in women, calcium from calcium sulfate set tofu was absorbed about as well as milk calcium. No dog trial exists, and at gelling doses it adds only a little.4,8
-
Critics say
It's plaster of Paris, drywall in dog food
Outruns the evidence
Evidence
- Strong
- Some
- Thin
- None
Same mineral, different grade. FDA names plaster of Paris and gypsum in its safe listing for human food, requires Food Chemicals Codex purity, and allows up to 1.3% in baked goods.1
-
Owners say
Sulfate additives are harmful chemicals
Outruns the evidence
Evidence
- Strong
- Some
- Thin
- None
EFSA's 2019 review found sulfates low in acute toxicity, with no genotoxicity or cancer concern and no need for an intake limit. Laxative effects in people began near 207 mg sulfate per kg body weight, from a more soluble salt.3
Straight answers
What owners ask
-
Q01
Is it just filler?
NoIt works at a percent or two and has a specific job: its calcium sets the gel that holds chunks and sauce together. A filler would add bulk with no function.6
-
Q02
Is it the same as drywall?
Same mineralBoth are gypsum. The human food version must meet Food Chemicals Codex purity, and FDA treats feed use as safe under good manufacturing practice. Grade, not chemistry, is the difference.1,2
-
Q03
Does it change urine pH?
BarelyIn a 42-cat trial, adding it moved urine pH from 6.89 to about 6.6, a change that was not statistically significant, and methionine sources acidified more. No dog data exists.7
Who uses it
Brands, best sellers and the company it keeps
Top brands, by foods that list it
Usually listed with, share of the foods that list it
- Chicken Broth 100%
- Tapioca 100%
- Flaxseed 100%
- Sunflower Oil 50%
- Sodium Hexametaphosphate 50%
- Marine Microalgae Oil 50%
- Choline Chloride 50%
- Minerals 50%
- Carrots 50%
- Peas 50%
- Brown Rice 50%
- Sodium Tripolyphosphate 50%
On the shelf
Foods that list it
2 foods in our reviews list it. Here are some of them.
Our read // On the bag
Read it as a texture aid and move on
In a wet food it sits near the end of the list, beside gums, gelling agents and other minerals, because it works at a percent or two. It tells you the food has a gel or chunk texture. Judge the food by its meats and its guaranteed analysis instead.
Sources
What we read
Checked October 1, 2026.
- 1 21 CFR § 184.1230 - Calcium sulfate
- 2 21 CFR § 582.5230 - Calcium sulfate
- 3 Re-evaluation of sulphuric acid and its sodium, potassium, calcium and ammonium salts (E 513, 514 (i), 514 (ii), 515 (i), 515 (ii), 516 and 517) as food additive
- 4 Gypsum: an old product with a new use
- 5 Feed Grade Calcium Sulfate
- 6 Continuous production of gelled chunks of foodstuffs (US4784862A)
- 7 Different sources of sulfur in diets of adult cats on the urinary parameters and acid-base balance
- 8 Bioavailability of calcium from tofu as compared with milk in premenopausal women
- 9 A Look at US Gypsum Production