Water activity: A better moisture metric for pet food
Find the ideal water activity range for your pet food product that maximizes profit, nutrition, and tastiness while keeping it safe from microbes and mold.
Moisture plays a key role in the quality of pet food products. For each product, there’s an ideal range of water activity values that maximizes profit, nutrition, and tastiness while keeping the product safe from microbes and mold.
For example, a bag of dog food kibbles has a moisture sweet spot of 0.55-0.65. Any lower than 0.55, and the dog food is unappetizingly dry and hard. Not to mention the seller is losing money because the product has been over-processed. Any higher than 0.65, and the product will mold in the bag, becoming unacceptable.
Water activity has been used to guide the formulation of some of the most innovative–and commercially successful–pet food products. Complex pet food formulations like a simulated marrow-filled bone, a meaty cat food containing crunchy vitamin bits, and a shelf-stable, moist, meat-like product are all controlled by water activity.
Isotherms (curves showing how water activity changes as moisture increases and decreases in a specific product) are also a key formulation tool. They can be used to locate critical points where phase changes occur, to create mixing models, to investigate moisture-related issues, and in many other ways.
Know the moisture super-spec
Using water activity as a moisture super-spec can help you solve specific moisture challenges, determine shelf life, choose packaging, monitor incoming ingredients, prevent spoilage, and maintain taste, texture, and nutrition.
For example, there are a number of products on the market with multi-textured characteristics that use water activity. These products combine a hard, dry-baked pet food and a soft, moist pet food. The hard, dry component has the advantage of teeth cleaning, but is less palatable than a soft, moist food. Careful formulation using water activity keeps the crunchy kibble crunchy and the moist bits soft. The two can share a bag and a long shelf life without the kibble getting soft and the bits losing their moist texture.
Make every employee a moisture expert
Water activity is a test anyone can run to precise scientific standards. A certification course trains new users to measure water activity. In 20 minutes, nearly anyone can learn to run a reliable, repeatable, verified water activity test.
Moisture measurement with benefits
Pet food manufacturers use water activity to monitor their products because:
It accurately predicts safety: Water activity predicts whether microbes will grow on or in a product.
It also predicts quality: Water activity is correlated with many reactions (lipid oxidation, vitamin degradation, texture changes) that end shelf life.
It’s repeatable: Water activity is a test anyone can run to precise scientific standards. Measure water activityto ±0.003.
It’s standards based: Unlike other moisture measurements, water activity has a scale with a known zero, and measurements can be verified with known, NIST-traceable standards. Results can be compared between departments, factories, or companies no matter where they’re located or who makes the measurement.
Table 1. Water activities that correlate to the growth of microorganisms in pet food. Water activity is directly related to mold and microbial growth and is an integral part of many HACCP programs. Chart adapted from L.R. Beuchat, Cereal Foods World, 26: 345 (1981).
Microorganisms Generally Inhibited by lowest aw in this Range
Pet Foods Generally Within this Range
Pseudomonas, Escherichia, Proteus, Shigells, Klebsiella, Bacillus, Clostridium perfringens, some yeasts
Pedigree–Little Champions Meow Mix–Tender Favorites Pedigree–Little Champions Purina–Beneful Prepared Meals
Salmonella, Vibrio parahaemalyticus, C. Botulinum, Serratia, Lactobacillus, Pediococcus, some molds, yeasts (Rhodotorula, Pichia)
Canine Carry Outs–beef
Many yeasts (Candida, Tarulopsis, Hansenula), Micrococcus
Purina–Moist & Meaty Dog Food
Most molds (mycotaxigenic penicilla), Staphyloccocus aureus, most Saccharomyces (bailiii) spp., Debaryomyces
Cesar–Softies Canine Carry Outs–bacon
Most halaphilic bacteria, mycotoxigenic aspergilli
Xerophilic molds (Aspergillus chevalieri, A. candidus, Wallemia sebi), Saccharomyces bisporus
Milk Bone–Trail Mix
Osmophilic yeasts (Saccharomyces rouxii), few molds (Aspergilius echinulatus, Monascus bisporus)
Iam's ProActive Health–MiniChunks Natural Life Grain-Free–adult dog Wiskas–Temptations
Set a spec for product to avoid safety and quality issues such as mold, microbial growth, texture problems, off smells or flavors
Eliminate variability with a standards-based moisture metric
Use water activity to guide innovative formulations
Market snapshot: Pet food top competitors
We bought bags of kibble from a variety of retailers. We tested big brands alongside small niche companies. The result? A market snapshot of thirteen pet food brands. In this quick 15-minute webinar, Scott Campbell reviews the findings.
which brands came close to exceeding the 10% moisture limit.
what some big brands do much better than small ones.
which brands over-pack—and which ones don’t quite meet the minimum.
the projected costs of inconsistency in packaging and drying.