A Department of Agriculture (USDA) regulation introduced to eliminate rare cases of salmonella in raw almonds has prompted many California almond processors to install steam pasteurization equipment that achieves a four-log reduction of the bacteria (a 10,000-fold decrease).
In most installations, the pasteurization equipment is oriented horizontally, but one top-10 (worldwide) almond producer in Ballico, Calif., has taken a different approach. At Hilltop Ranch, the almonds to be processed flow downward by gravity in a zigzag pattern through a vertically oriented, 22' pasteurization chamber. This enables steam to be utilized throughout the column more efficiently, according to the company, reducing energy consumption, treating all almond surfaces uniformly and reducing the equipment footprint by approximately 50 percent.
To further reduce energy consumption and floor space requirements, Hilltop Ranch pursued a fresh approach and installed two circular, vibratory fluid-bed processing systems from Kason Corp., Milburn, N.J., for drying and cooling the pasteurized almonds.
Complementing the Pasteurization Process“Although the original pasteurization process was designed to incorporate horizontal fluid bed processors, circular units from Kason caught our interest,” says Charlie Jahn, quality manager for Hilltop. “We considered a few fluidized bed processors and had some initial testing done with a conventional rectangular system. Most work well, but they’re twice as large, so they require extensive infrastructure and ancillary equipment, as well as energy-consuming levels of airflow.”
According to Jahn, a fluid bed processor had not previously been used at Hilltop for drying or cooling of almonds, so he first he had to establish specifications for several criteria such as:
- The heat and moisture ranges required
immediately after pasteurization.
- The cooling requirements after drying.
- The throughput requirement of 22,000 lb/hr (9,979 kg/hr) of almonds.
Dexter Long, vice president of operations at Hilltop, explains, “We chose the Kason fluid beds based on test results for both drying and cooling, and because the company guaranteed those results if we could supply the minimum temperatures for drying and maximum temperatures for cooling operations. We like small footprints and vertical systems around here, so after the testing and one customer recommendation, we ordered the two circular vibratory fluid bed units. They were easy to install, easy to operate and clean, and they’re working efficiently as guaranteed.”
The circular fluid bed processor offers a higher strength-to-weight ratio than rectangular units of equivalent capacity, according to David Long, founder of Hilltop Ranch, and does not require heavy steel sidewalls or cross braces to withstand extensive vibration. The inherent strength of the circular unit also allows materials of construction to be down-gauged and gyratory motors to be downsized. The unit’s small, circular footprint was also desirable to the company, which opted for an 84" diameter model, the largest currently offered.
Drying Pasteurized AlmondsImmediately following steam pasteurization, the elevated moisture content of almonds must be returned to between 4.5 and 5.5 percent, because at only 6.8 percent moisture, the almonds would become too soft and have a shorter shelf-life.
To remove excess moisture, almonds exiting the vertical pasteurization chamber are metered by a rotary airlock valve into the circular fluid bed dryer. Imbalanced weight gyratory motors cause the almonds to vibrate on a perforated plate within a rising column of heated (180°F [82°C] minimum) air blown into the center of the fluid bed chamber from below by a 25 hp (18.6 kw) variable-speed fan. Continuous airflow and vibration separate and fluidize individual almonds, maximizing the rate at which drying occurs. The vibratory motion also serves to convey the almonds in a controlled spiral pathway from the center to the periphery of the chamber on a first-in/first-out basis with a dwell time of approximately 1 min. The vibratory motion then conveys the almonds to evacuate the chamber at the end of each cycle.
Cooling Dried AlmondsHeated almonds exit through a discharge spout at the periphery of the fluid bed dryer and are elevated 35' by a Cablevey drag conveyor to a Kason circular vibratory fluid bed cooler, which differs from the dryer in only one respect. Instead of a thermal fluid heater with blower to introduce warm air, it is equipped with a heat exchanger (plumbed to a plant chiller) and blower to force cool (65°F [18.3°C] maximum) air into the center of the fluid bed chamber from below. The system cools the almonds to ambient temperature or less after a dwell time of approximately one minute.
Because rapid cooling creates a difference between the exterior and interior temperatures the almonds, they next are gravity-fed into a vertical-cone equilibration tank in which ambient air is blown onto the almonds. The tank walls are inclined at 70° to ensure that the almonds pass through on a first-in/first-out basis for uniform equilibrating.
“The equilibration step may be unique to Hilltop,” says Jahn. “The almonds are mostly equilibrated after a minute in the Kason fluid bed cooler, but their interior temperature is marginally warmer than the exterior, so we added this 30-minute step. Our quality-control ‘sweat-test’ indicates that this step eliminates all residual moisture and condensation during packaging, a problem we know that other processors have experienced. The whole vertical pasteurization process takes a little over 30 minutes, with most of that time spent in the equilibration tank.”
With Hilltop’s long history of innovative processing solutions, it’s likely that the vertical almond processing will not be its last unconventional approach to processing challenges.
For more information about circular fluid bed drying and cooling systems from Kason Corp., call (973) 467-8140; e-mail firstname.lastname@example.org; or visit www.kason.com. For more information from Hilltop Ranch, visit www.hilltopranch.com.