With the pending implementation of the Food Safety Modernization Act and increasing consumer demands, animal feed safety is under closer scrutiny. Particularly, Salmonella contamination has been identified as a potential biological pathogen of concern in the pet food industry, and has been the cause of several recent pet food recalls. The industry is in search of potential methods to lower the risk of Salmonella in animal feed. One potential method of Salmonella mitigation is through the use of acidifiers to reduce pH to destroy or inhibit growth of bacteria. The objective of this experiment was to determine if coating pet food with a dry acidulant powder, sodium bisulfate (SBS, Jones-Hamilton, Co., Waldridge, OH), would reduce Salmonella growth over time in dog foods of varying surface area, bulk density and piece density. A single formula of a dry dog food was utilized in a 4 × 3 factorial design with 4 kibble sizes (surface area of 455, 997, 1,022, or 7,337 mm²) and 3 coating levels of SBS (0.0, 0.2, or 0.4%). The results were tested over a 14-d period with sampling day serving as a repeated measure. Kibble sizes were analyzed for surface area, bulk density, and piece density. Then, kibble was coated with varying levels of SBS and inoculated with a Salmonella cocktail (ATTC# 13076) on d 0 and analyzed for Salmonella on d 0, 1, 2, 7, and 14 by direct plating to xylose lysine deoxycholate agar. Bulk density, piece density, and surface area were not correlated with Salmonella quantity (P > 0.10), and there was no effect (P > 0.10) of kibble size or the interactions including kibble size on Salmonella concentration. However, coating kibble with SBS resulted in a 1.6 or 2.0-log reduction in Salmonella (P < 0.0001; 1.23 or 1.65 vs. 3.27 log₁₀ cfu/g for 0.4 or 0.2 vs. 0.0% SBS inclusion, respectively). Time also had a substantial effect on Salmonella concentration, and reduced Salmonella by 3.41 logs by 14 d post-inoculation (P < 0.0001; 4.10, 3.04, 1.47, 0.97, 0.69 log₁₀ cfu/g for d 0, 1, 2, 7, and 14, respectively). In conclusion, both time and the coating of kibble with a dry acidulant substantially reduce Salmonella concentration in the tested product. However, altering the size of kibble does not further reduce the risk of Salmonella in a dry extruded dog food.