CUSTOMER TECHNICAL INSIGHTS, AFB INTERNATIONAL Overview Moisture content (MC) in dry pet food is often underestimated. Manufacturers typically associate it with mold risk, overlooking its impact on palatability. While the link between MC and kibble palatability is generally acknowledged, it remains rarely quantified, leaving many questions unanswered. This study provides...
Leveraging Moisture to Improve Dry Pet Food: Quality
CUSTOMER TECHNICAL INSIGHTS, AFB INTERNATIONAL
Overview
Part I of this whitepaper explored the impact of moisture content (MC) on dry pet food palatability. However, MC optimization must also take the kibble quality into account.
This Part II reviews the key quality parameters to consider when adjusting MC, and provides supportive data to guide implementation.
Water Activity
Water activity (aw) measures the amount of free (unbound) water in a product that is available to support microbial growth and biochemical reactions. For assessing dry pet food quality, aw is more relevant than MC. The aw stability diagram shown in Figure 1 illustrates the effects of aw. In dry pet food, yeasts and bacteria growth are generally not a concern, as they require aw values above 0.8 and 0.9, respectively.
Results
Each MC increment was tested vs. the control kibble, and the results are presented in Figure 1. As the moisture gap widened, intake ratios (IR) favored drier kibbles for cats and wetter ones for dogs. For cats, statistically significant differences emerged from the third test onward (α = 0.05), although a decreasing trend in p-values was already apparent. In dogs, significance was observed from the first comparison.
Figure 1. Water activity stability diagram, adapted from Labuza (1970).
Figure 2. Example of a typical evolution of aw with MC on coated kibbles. Blue area shows the average MC/aw of cat.
Figure 2 gives an example of how aw can evolve with MC in coated dry kibbles. While both cat and dog kibbles typically remain well below critical thresholds, mold growth can occur from aw 0.62, a level that dog kibbles may reach at around 10 % MC. This is the primary risk zone to monitor when increasing MC.
Although aw is easy to measure, it remains difficult to predict, as its relationship with MC is not linear. Some ingredients act as humectants and can lower aw at a given MC (e.g. salt, proteins, or soluble fibers). Conversely, liquid palatants can significantly increase aw of kibbles. Figure 3 shows an example of how coating with a liquid palatant can affect the aw of cat kibbles. Based on the trend observed in uncoated kibbles, one might expect an aw of coated kibbles around 0.44 at 7-7.5 % MC. However, the measured aw is closer to 0.5. This difference can be explained by the nature of water involved: liquid palatants contribute mainly free water, while the residual water from drying in uncoated kibbles is more tightly bound within the matrix. As such, liquid palatant coating is a key parameter in aw management.
Figure 3. Example of aw and MC of coated and uncoated cat kibbles.
Other Considerations
While aw remains the primary concern when adjusting MC, other quality parameters must also be considered. As shown in Figure 1, lipid oxidation can increase when aw drops below 0.2 or rises above 0.6, due to greater free radical mobility. Additionally, excessive drying makes kibbles more brittle, leading to higher levels of breakage and fines during coating, sieving and conveying processes.
Drying & Coating Efficiency
MC optimization in cat kibbles is about finding the right balance between palatability, cost and quality. In dog kibbles, it means pushing MC as high as technically feasible, while avoiding any risk of mold development.
A critical factor is MC variability, which directly affects aw. While drying is the main source of this variability, the coating step also contributes significantly. As shown in Figure 2, liquid palatants not only increase MC, but have an even greater impact on aw. If poorly controlled (e.g. insufficient spraying or mixing time, too few nozzles, incorrect nozzle orientation), coating can introduce substantial inconsistency.
Figure 4 illustrates that when sampling is limited to a single time or location, this variability may go undetected. Readings may appear acceptable, while some kibbles remain at risk. MC management should aim for a coefficient of variation (CV) below 5 %. A CV between 5-10 % is tolerable but calls for improvement. Anything above 10 % requires immediate corrective action.
Figure 4. Examples of poor (left) and good (right) drying and coating management.
Conclusions & Discussion
Effective MC management is essential to optimizing dry pet food production. However, implementing MC changes (whether by adjusting drying parameters or coating conditions) requires a methodical step-by-step approach to avoid compromising product quality.
Importantly, MC and aw should not be viewed as simple average values. To mitigate risk (especially for export), drying and coating efficiency must be assessed, with a focus on identifying and reducing variability.
To learn more about this topic, or to speak with our Customer Technical Insights experts, please reach out to your AFB Sales representative or afbinternational.com/contact.