Kibble coatings: fats, digests and palatants after extrusion

Mehta, Priya

Kibble coatings: fats, digests and palatants after extrusion

What goes onto kibble after the dryer, why the method, order and timing of each layer change palatability and shelf life, and a troubleshooting table for the faults we see most often.

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By Priya MehtaGuires PNL scientific team

Reviewed byGuires PNL nutrition science and regulatory teams

Published2 Nov 2026

Last checked2 Nov 2026

Reading time7 minutes

Key takeaways

Most dry food leaves the dryer lean and porous; fat, liquid digest, dry palatant and any probiotic are applied afterwards in a drum or vacuum coater.
Vacuum coating draws more fat into the pores and suits high-fat or dense kibble; below about 2% coating, kibble tends to look patchy.
Timing matters: in a 40-cat study, adding powder palatant 24 hours after the fat improved palatability at every fat level tested.
Probiotic claims on coated kibble need end-of-shelf-life counts; one survey found no diet contained all its listed organisms.

Kibble coating layers: porous extruded core, fat and liquid digest layer, and dry palatant on the surface

EvidenceGoodRated by the Guires Pet Nutrition Lab scientific team

TopicFat, digest, palatant and probiotic coatings on extruded dry pet food

Key leversCoating method (drum or vacuum), order and timing of each layer

Use it forPalatability problems, coating faults and shelf-life failures

01The short answer

What goes onto kibble after extrusion? Most dry food leaves the dryer as a lean, porous base. It is then coated in a drum or vacuum coater, usually with fat and liquid digest first and dry palatant second. The fat adds energy and carries aroma, the palatants drive acceptance, and heat-sensitive actives such as probiotics can go on last. The method, order and timing of each layer decide how the food performs in the bowl and on the shelf ¹².

For the upstream process, see our guide to how kibble is made.

02What goes on the kibble

A coated kibble usually carries up to five layers or components. Each has a different job and a different way of failing.

Coating layer	Typical examples	Main job	How it is applied	Watch out for
Fat or oil	Poultry fat, tallow, fish oil, vegetable oil	Energy, texture, aroma carrier	Warmed to liquid, sprayed in a drum or under vacuum	Greasy kibble and fat migrating into the bag, especially in warm conditions ¹; oxidation
Liquid palatant (digest)	Hydrolysed poultry liver, meat and organ digests ³	Base flavour, first-bite appeal	Sprayed with or just after the fat	Oxidation of the digest; batch consistency
Dry palatant	Powdered digests, yeast-based ingredients, dairy and organic acid components ³	Surface aroma, top note	Dusted after the liquid stage	Gets buried if the fat is still liquid ²
Antioxidants	Mixed tocopherols, rosemary extract	Protect fat and digests from oxidation	Blended into the fat before coating	Ethoxyquin is no longer authorised as a feed antioxidant in the EU ⁷
Functional actives	Probiotics, heat-sensitive vitamins, botanicals	Carry claims that would not survive extrusion	Top-coated after cooling	Viable counts at the end of shelf life ⁵⁶

Table 1. Coating components of extruded dry pet food and their main risks.

03What the evidence says

Coating method changes fat uptake

Vacuum coating draws more of the applied fat into the kibble than atmospheric drum coating. It matters most for high fat levels and for dense, low-porosity kibble. At the other end, less than about 2% fat or liquid palatant tends to leave the coating uneven and the kibble dull ¹.

	Atmospheric (drum)	Vacuum
Where the fat goes	Mostly on and near the surface	Drawn into the internal pores as pressure is released
Best suited to	Moderate fat levels, porous kibble	High fat levels, dense or low-porosity kibble ¹
Powder palatant at the surface	Falls as more fat is applied ²	Higher at high vacuum ²
Cost and complexity	Lower; continuous drum	Higher; batch vessel and vacuum system

Table 2. Atmospheric and vacuum coating compared. The cost row is our process experience, not from the cited studies.

Order and timing matter as much as method

A DIANA Pet Food study coated kibble with 8%, 11% and 14% poultry fat and 2% powder palatant, using four procedures, and ran 2-day two-bowl tests with 40 cats. Adding the powder 24 hours after the fat, still at atmospheric pressure, significantly improved palatability at every fat level compared with adding it straight after the fat. Under standard atmospheric coating, the more fat was applied, the more powder was buried. High vacuum (300 mbar) left more powder at the surface, and vacuum tended to improve palatability, most clearly at high fat. Total powder on the kibble was similar in every case: what changed was how much the cat could smell and taste ².

Palatants are formulated systems

Digests are made by chemical or enzymatic hydrolysis of clean animal tissue. Typical application rates are about 0.5–2% for dry palatants and 1–3% for liquids, although one patented system coats kibble with 4–8% of a beef digest and lipolysed tallow blend ³. Our palatants review covers how these systems are built.

The test shapes the result

Two-bowl tests measure preference; one-bowl tests measure acceptance. Most research groups now feed about 20 animals for 2 or 4 days. They report the intake ratio, each food’s share of total intake, so that differences in animal size do not skew the result ⁴.

Probiotic coatings need proof

In wheat-flour dog biscuits, a starch-glycerol coating kept Lactobacillus plantarum above 10⁸ CFU/mL (as reported) after one month of storage. The coating did not help a soy-based biscuit ⁵. In the market, a survey of 19 commercial dog and cat diets with probiotic claims found that none contained all the listed organisms, and 26% grew no relevant bacteria at all ⁶.

04What it means in a recipe

Design the base kibble for its coating. Porosity and bulk density are set at the extruder, and they decide how much fat the kibble can hold. Add the antioxidant to the fat when it is received, not at the coater, so the fat is protected while it is stored.

Figure 1A typical coating sequenceFrom the dryer to the bag

1 · DryerLean, porous base kibble
2 · Fat and digestDrum or vacuum coater
3 · Cool and setFat solidifies on the surface
4 · Dry palatantPowder stays at the surface
5 · Probiotic top-coatLow temperature, low moisture
6 · PackBarrier packaging

Letting the fat set before the powder goes on kept more palatant at the surface and improved palatability in cats ². Use vacuum at step 2 for high-fat or dense kibble ¹.

Coating troubleshooting table

Symptom	Likely cause	First fix
Patchy, dull kibble	Coating level below about 2%, poor spray pattern or drum fill	Check nozzles and fill level; review the coating level ¹
Greasy bag, fat pooling	Too much fat, or kibble too dense to absorb it	Vacuum coat, lower bulk density or cut fat ¹
Palatability drops after scale-up	Powder palatant buried in liquid fat	Apply powder after the fat sets; consider vacuum ²
Rancid odour before best-before	Fat or digest oxidation	Antioxidant at fat intake; track peroxide value; barrier packaging
Probiotic claim fails at end of shelf life	Heat, moisture or water activity too high	Coat after cooling; consider spore-forming strains; test counts at end of life ⁶
Fines and dust in the bag	Fragile kibble, aggressive tumbling	Lower drum speed; tune expansion upstream
Palatability swings between batches	Digest lot variation, coating temperature drift	Tighten digest specifications; control fat and drum temperature

Table 3. First fixes from the cited sources and Guires PNL pilot-plant experience. Uncited rows are our experience.

Guires Pet Nutrition Lab verdict

A coating is right when the palatant is still at the surface, the fat is still fresh and the probiotic count still meets the label at the end of shelf life, not when the kibble looks glossy off the line.

05For brands and formulators

Coating is where small changes show up fastest in the bowl. A new fat source, a switch from liquid to dry palatant, or a move to vacuum coating can lift or sink acceptance, and it can shorten shelf life.

06Questions brands ask

What is kibble coating?

It is the step after extrusion and drying where fat, liquid digests, dry palatants and sometimes functional ingredients are applied to the outside of the kibble in a drum or vacuum coater.

Why is fat sprayed on dog food after extrusion?

Fat in the mash reduces expansion and raises bulk density, so most of a dry food’s fat is applied after drying. This dog food coating raises energy, improves texture and carries aroma.

What is the difference between dry and liquid palatants?

Liquid palatants, usually digests, give the base flavour and go on with or just after the fat. Dry palatants are powders dusted on last for surface aroma, and stay more available when the fat has set first.

Do probiotics survive on coated kibble?

They can, if they are applied after cooling and protected from heat and moisture. Market surveys have found diets below their label claims, so viable counts should be tested at the end of shelf life.

Sources

Ward L (2025). Texture matters: the role of coatings in extruded pet food. GlobalPETS, 11 February 2025. Source ↗
Revéret É, Bramoullé L. Impact of fat coating procedure on powder palatant availability and performance in cats. DIANA Pet Food white paper (undated). Source ↗
Samant SS, Crandall PG, Jarma Arroyo SE, Seo HS (2021). Dry pet food flavor enhancers and their impact on palatability: a review. Foods 10(11):2599. Source ↗
Aldrich GC, Koppel K (2015). Pet food palatability evaluation: a review of standard assay techniques and interpretation of results with a primary focus on limitations. Animals 5(1):43–55. Source ↗
González Forte LDS, Bruno DE, Martino M (2014). Application of coating on dog biscuits for extended survival of probiotic bacteria. Animal Feed Science and Technology 195:76–84. Source ↗
Weese JS, Arroyo L (2003). Bacteriological evaluation of dog and cat diets that claim to contain probiotics. Canadian Veterinary Journal 44(3). Source ↗
Commission Implementing Regulation (EU) 2022/1375 of 5 August 2022 concerning the denial of authorisation of ethoxyquin as a feed additive (antioxidants) and repealing Implementing Regulation (EU) 2017/962. Source ↗
Rokey GJ, Plattner B, Souza EM (2010). Feed extrusion process description. Revista Brasileira de Zootecnia 39 (suppl.):510–518. Source ↗

Evidence reviewed by the Guires Pet Nutrition Lab scientific team. This article is general information for product developers and is not legal or veterinary advice.

How to cite this article

Choose your referencing style, then copy. Check your university’s, journal’s or regulator’s guide for local variations.

Mehta, P. (2026, November 2). Kibble coatings: fats, digests and palatants after extrusion. Guires Pet Nutrition Lab Insights. https://www.petnutritionlab.com/insights/kibble-coatings-fats-digests-palatants

This article summarises published evidence for product developers. Cite the original sources above for specific findings, and do not reproduce this article as your own work.

Developing or fixing a coated dry food?

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