Improve yields and consistency in your smokehouse
The breakpoint is the most important feature in an industrial smokehouse and dehydrator.
It is ultimately responsible for cooking your product and has a direct effect on product yields and consistency.
And yet, most people don’t even know what the breakpoint is.
It’s why we put together this guide — to help you understand what the breakpoint is, how it affects your product, and how to improve it to get better yields and consistency.
Back in the late 1950s, an innovative new way of cooking products in the meat processing industry was discovered — an innovation that is still in use in industrial smokehouses and dehydrators today.
This innovation incorporated the use of alternating dampers in forced-air ovens so air from a single fan could be delivered to the product on racks.
The alternating dampers on either side of the oven create two opposing airstreams in the oven cabinet. The location where these opposing airstreams collide is called the breakpoint.
The breakpoint is the location where two opposing airstreams in the oven cabinet collide and move either horizontally or vertically through the cabinet (depending on the location of the breakpoint) to cook the product.
The breakpoint is formed by a combination of the fan, alternating dampers, and the corresponding high and low-velocity airflows created in the oven.
The airflow created by the fan enters the supply duct and hits the alternating dampers. The damper that is set to block the duct creates the low-velocity airflow while the damper set to open creates the high-velocity airflow. These differing airflows are on opposing sides of the oven.
The high-velocity airflow travels down the oven wall, across the floor, and up the opposing side. The low-velocity airflow travels a much shorter distance, hence being low velocity.
The collision of the low-velocity airflow and the high-velocity airflow causes the air to break towards the center of the oven — forming the breakpoint.
When formed correctly, the breakpoint has enough velocity to penetrate through the product on your rack before the air is drawn back to the return duct. It’s this breakpoint air that ultimately cooks your product.
The velocity of the breakpoint air as it moves across the product on the rack essentially wipes away a layer of cold air surrounding the product and replaces it with hot air.
As the breakpoint moves throughout the oven cabinet, it wipes away more and more layers of cold air surrounding the product.
The hot air left behind is eventually transferred to the product, cooking it to the required temperature.
The breakpoint plays a critical role in the consistency of your product and is often to blame for poor product yields (or the remaining weight of your product after cooking).
Most commercial ovens utilize continually oscillating airflow with minimal or weak breakpoints, resulting in inconsistent product coloring and yields. Product closest to the outside edges and bottom of the truck is cooked faster and more thoroughly, while products in the upper-middle and insides of the truck cook slower.
The varying rates of cooking caused by fewer and weaker breakpoints in the oven lead to higher yield gaps: where some product on your rack is over cooked and other product is cooked just right.
As you have likely experienced, this results in inconsistent product yields and coloring. The product closest to the breakpoint often can be burnt, darker, and in some cases, needs to be thrown out, while the product furthest from the breakpoint achieves the color desired.
Imagine the difference in your product if there were more breakpoints in the oven! Rather than needing to overcook the product closest to the breakpoint so that the product furthest from the breakpoint can be cooked, there would be more and stronger breakpoints — meaning less product would be away from the breakpoint.
When there are more and stronger breakpoints in the oven, you eliminate those cold spots and your product cooks more consistently.
There are two methods widely used to control the breakpoint in a smokehouse or dehydrator:
The oven is built with two identical fans that operate in opposition to each other in order to create high and low-velocity air streams. All the work of creating and controlling the breakpoint lies in how the fans work in relation to each other.
The oven is built with a set of alternating dampers in the cabinet’s air supply duct. These dampers are set opposite of each other in a 90° formation to create the high and low-velocity air steams. The dampers create and control the breakpoint.
There are five main factors that help create and allow you to control a strong breakpoint throughout the oven, that you can see to the right.
When all five factors are applied correctly, you are able to control the location and duration of the breakpoint to optimize your cook cycle and increase product consistency and yields.
The design of how the side walls and floor meet will either enhance or degrade the velocity of the air streams, resulting in either a stronger or weaker breakpoint, respectively. Many oven manufacturers use a 90° or 45° angle between the walls and floor, which results in the air stream degrading once hit hits those angles.
A radius, or cove, design along the bottom of the walls gently pushes the airstream along the floor, maintaining the air stream velocity and resulting in a stronger breakpoint to make it across the rack and evenly cook product.
The design of the supply duct plays a large role in enhancing or degrading the breakpoint. The typical cone design found in most ovens allows the high and low-velocity airstreams to bounce around the cabinet, resulting in overcooking product on the edges and bottom of the cart.
A knife-point design with a width of around 1” keeps the high and low-velocity airstreams along the oven walls to maintain velocity and make the breakpoint stronger when the airstreams collide.
A study sponsored by the National Institute of Food and Agriculture, found when one supply slot was fully open and the other was closed, the Venturi effect actually pulled the air across the cabinet with only a slip-stream pulled up into the return duct.
This discovery led them to develop a re-designed return duct that extended the duct down into the cabinet to reduce the Venturi effect. The new extended return duct not only reduced the pull of the Venturi, it also unexpectedly produced the most uniform, highest velocity airflow of all the test runs. The anemometer and fog machine data showed that the extended return duct favored pulling air through the historically “cold-spot” that exists at the top-center of conventional designs — generating the most uniform airflow and higher velocity air through all areas of the cabinet, including the “cold-spot.”
Using the extended-return duct in combination with the variable-width supply slots created much more uniform air velocities through the “cold-zone” at the top-center of the cabinet than conventional designs. Also, when used in further combination with the new high-volume air kit, the air velocities were measurably more uniform and almost double those of conventional designs.
Placing a truck in your oven affects the flow of the high and low velocity airstreams that create the breakpoint. Any obstruction in the oven cabinet will cause the air flow to change — meaning the design and placement of the trucks you use in your oven is critically important.
The final piece of the breakpoint puzzle is damper positioning. The ability to position the dampers at varying degrees and keep them in place for long periods of time (rather than a continual rotation), allows you to control exactly where the breakpoint occurs in the oven.
The breakpoint needs to be positioned at the height of the product, not too high, which bypasses the product envelope, and not too low that it is not directing airflow to the upper corners of the product envelope.
Adjusting the angle of the dampers allows more or less airflow into the oven cabinet. As the dampers adjust, the velocity of the air released changes — either increasing or decreasing the high velocity airflow to go further or less in the oven. When the airflows change velocity, the point where they collide (the breakpoint) changes locations in the oven.
The speed at which the breakpoint moves is dependent upon the damper shaft’s revolution per minute.
In order to get good heat transfer and enough exposure to the oscillating airflow for even drying of product, the RPM of the supply airflow dampers should run between 0.25 and 0.5 RPM, or its equivalency if the dampers move back and forth from 0 degrees to 90 degrees.
