How Simmons Foods found the sweet spot

The art of extrusion

Stoller got his start in food processing by working on and around extruders, the equipment used to make products like pet food. A welder by trade, Rick worked his way up to service technician, where he traveled around the country, starting up and servicing extruding equipment for over a decade.

“It’s an art to get the kibble perfect,” Stoller says. “You can’t replicate it every day. You can put guidelines down, but until you actually get behind the wheel, it’s like the road changes every day.”

That winding road is where the benefits of having a roadmap of analytics can be the difference between making it to the finish line and coming up short.

Water activity and moisture content in dry foods

Initially, moisture content was more of a focus than water activity. Being able to consistently dry to a target water activity would bring moisture content in line, as long as formulations and processes were right. 

But removing moisture from any food can have several effects, one being the palatability of the product. Too moist or too dry and the food becomes unpleasant to consume. 

However, another factor that processors look at is profit. We can think of moisture as money. Drying takes time and money, so over-drying for the sake of food safety can start to affect the bottom line. But under-drying can lead to food safety concerns. 

This is where water activity comes in. Balancing the water activity of the product with the moisture content allows for highly palatable foods that maintain the highest level of food safety and save the most money during processing.

Water activity is also a great indicator of process control. As Stoller says, “Water activity really has helped us troubleshoot and dial in all of our other analytics. It’s one of the analytics that pinpoint where we may be having a problem or be running out of spec. It’s a very quick indicator to tie in and troubleshoot.”

When to measure water activity

Water activity measurements are important to time correctly. Measure too late in processing and it’s difficult to divert the product down a different route. For Simmons, this timing is critical. As a part of their HACCP, Simmons checks water activity first at the extruder. Stoller also has checks before the kibble is loaded into the finished product bins. This way, if levels are out of spec, the batch can be directed away from packaging for further processing.

Rick’s used these water activity measurements to home in their other analytics as well. “This started as a moisture project and then rolled into water activity,” he says. This shift has allowed Simmons to tighten their other specifications for even better process control.

All of their analytics are then sent in real-time back to the extruder operators to see and adjust processing, with water activity being the determining factor for problems.

Using water activity for continued improvement

“We don’t focus on hitting max spec. We focus on hitting our targets,” Stoller says. Now that water activity is under control, Stoller can drive forward with moisture content, bringing back unrealized profits for Simmons. This focus on targets and analytics allows the company to deliver exactly what the customer orders.

Another area of improvement is with incoming ingredients. Stoller manually spot checks water activity of their bulk ingredients, but there’s an opportunity for automation to check water activity and other control points to tighten up specs before it enters processing. 

But every product in the Simmons lineup is unique. Each recipe has its own isotherm, or its correlation between water activity and moisture, and keeping these two measurables in balance is the key to having food safe, high quality kibble. In the past, Stoller admits that they’ve erred on the side of caution and perhaps over-dried the kibble more frequently, and without the understanding of water activity and moisture content, this seems like the sensible thing to do.

But Simmons has been able to reduce drying time on some of their recipes that are allowed a higher moisture content, as long as the water activity is within spec. 

As Stoller says, “For a company like ours with so many different formulas, those isotherms are essential.”