History of Blast Chilling
Cooked, partially cooked or “heat treated” meat and poultry products must be stabilized by cooling to prevent the growth of spore-forming bacteria. Best stabilization guidelines, FSIS Appendix B, require “that cooling be continuous through the given time/temperature control points”. But, how many or how few plant chilling devices can demonstrate control points being reached reliably so that random sampling of production lots can never challenge a plant’s validated processes?
The Process of Chilling Meat Efficiently Requires More Than a Recipe
The meat and poultry industry has long been suffering from a lack of understanding of what is required to chill their products efficiently and uniformly. Just as we may dial down our home refrigerator to a setting where milk is perfectly chilled only to find that soda cans have frozen and popped, processors’ first instinct is also to turn the dial down while degrading their products in the course. The refrigeration contractors that processors relied upon knew how to make air colder, cold enough to theoretically bring about convective heat removal, but understood very little about the thermal conductivity of the processor’s products. The result was that errantly crusted product later became sour as the unwanted layer of ice crystals “locked” the product, preventing it from aspirating heat and moisture naturally.
Cold air cannot be circulated and controlled in the same way that hot, moisture laden air is circulated and controlled. Circulation of cold air must be more precise, always through – and not around – the product mass and at a greater volume with variable control of velocity.
Marlen Industrial Chillers Yield Optimal Results
Surrounding product of any kind with “cold” has never been good enough. Prior to designing and engineering an efficient blast chill cell, Marlen examined the issue from the standpoint of the meat and poultry product’s needs. Different meat products with varying thermal properties have different abilities to give up heat and moisture. This is a physical reality that cannot be altered. By matching the abilities of the chilling apparatus to the thermal properties of the product – and just as importantly the processor’s objectives for that product – Marlen equipment yields the desired results.
Producing a chilling recipe for each product, similar to a cooking recipe, Marlen addresses the product’s need to aspirate naturally, giving up a precise amount of moisture and no more. The Marlen Blast Chill Cell adjusts itself to remove condensed moisture during an initial phase per the chilling recipe. The recipe then dictates adjustments to air velocity and chill temperature to step the product through the cycle with greatest efficiency. The chill recipe not only brings about the most rapid stabilization but does so with optimum uniformity – no “hot spots”, no errant crusting.
Called “looped airflow”, Marlen’s industrial chiller design calls for a massive volume of air to be moved – always through, not around – the product. With their better management of airflow, wasteful short-circuiting of the process media is eliminated, saving energy and process time. This advantage has been verified, independent of Marlen, in many blast chill cell installations. Processors using Marlen’s industrial chillers enjoy faster chill times and more uniform results as compared with other types of air chill systems. Airflow velocity of the chilled air mass is controlled, again by the specific recipe. Marlen moves air through the product with speed dictated by the products ability to give up its heat.
The Final Stage: Efficient Evaporation During Chilling of Meat and Poultry Products
When operating at colder temperatures, an undersized evaporator surface can produce errant crust-freezing of product thus degrading product quality. Excessive package purge is evidence of this damage. Crust freezing can also retard the thermal conductivity of the product preventing heat from reaching the surface in an efficient manner, slowing the cooling process. Therefore, immediate “deep chilling” practices are to be avoided.
Processors should insist evaporation surfaces are sized to a minimum of 12ᵒF operating differential across the coil itself. They should also be equally insistent that evaporator design and sizing take into full account the thermal conductivity of the product being processed. Also, any need to take product through the latent heat phase (chilling products below their freezing point) must be understood for proper equipment sizing. This match which results in surrounding the product with conditions that allow it to give up its heat most efficiently should not be compromised.
Marlen’s industrial chillers are equipped with tube and fin evaporators of 100% stainless steel construction. When coupled with Marlen’s highly efficient “looped airflow”, processors can meet guidelines for stabilization. But it is their electrolyzed aluminum fins that bring an extra margin of heat exchange efficiency that no other material can match. Concerns for safely sanitizing stainless/aluminum coils, with regard to the aluminum material, go away with Marlen’s dedicated clean-in-place (CIP) system.
Marlen’s website features additional technical information regarding critical elements of blast chill cell design.