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Why Nut Pasteurization

Are all Tree nuts Pasteurized?

Tree Nut Pasteurization
Is there a growing trend to pasteurize tree nuts worldwide? 

Common intuition certainly indicate that various tree nuts such as Almonds, Pistachios, etc. are low moisture foods.  Not surprisingly, they easily fit the FDA definition: “Low-moisture foods (LMFs) have been defined as those food products with a Water Activity (aw) less than 0.85 and are generally considered less susceptible to microbial spoilage and the growth of foodborne pathogens” (1)  This classification, however, does not by any means imply the product is inherently free of pathogenic organisms. 


Hence, the application of surface pasteurization treatments for tree nuts is becoming more commonplace.  Multiple factors influence a processors decision to install pasteurization systems including responsible business practice to ensure product safety, liability mitigation, product specifications from larger customers, as well as regulatory compliance since pasteurization of Almonds is now mandated by federal law.

Salmonella is a bacteria that commonly causes foodborne illness, sometimes called “food poisoning.” CDC estimates Salmonella causes 1 million foodborne illnesses every year in the United States. During the past few years, outbreaks of Salmonella illness have been linked to contaminated foods, including several types of nuts such as pistachios, almonds, cashews, and nut butters.


There is a growing trend and increased worldwide demand to pasteurize nuts and ensure the microbiological safety of the product with organic processes that maintain the organoleptic and nutritional characteristics of the tree nut.


CoolSteam refers to a forced convection system utilizing a homogeneous mixture of air and steam at temperatures below 212 F.  This mixture provides both condensational heating, and virtually simultaneous evaporation on the product surface due to the presence of air.  It’s an inherently gentle process, with much less moisture than 100% saturated steam, ideal for preserving product quality.   Forced convection is a well-accepted method of utilizing powerful fans to create a highly efficient environment for either heating or cooling.  It has the ability to literally force heat transfer coefficients up to 1000 times higher than static conditions but is controllable with a high degree of precision so just the right amount of heat can be applied, or removed, depending on the process objectives.

In total, this flexibility transforms the Laitram CoolSteam Pasteurization system into a powerful tool in the processor's arsenal, capable of responding to the challenges presented by real-world variability in raw product, always with complete assurance of achieving target lethality and food safety. 



Paul Favia

Crystal Process Equipment LLC

Consultant to Laitram Machinery

1 - Sánchez-Maldonado AF, Lee A, Farber JM. Methods for the Control of Foodborne Pathogens in Low-Moisture Foods. Annual Rev Food Sci Technol. 2018 Mar 25;9:177-208. doi: 10.1146/annurev-food-030117-012304. Epub 2018 Jan 12. PMID: 29328809

2 - FRANCISCO J. GARCES-VEGA ; ELLIOT T. RYSER ; BRADLEY P. MARKS  , Relationships of Water Activity and Moisture Content to the Thermal Inactivation Kinetics of Salmonella in Low-Moisture Foods. Journal of Food Protection (2019) 82 (6): 963–970.


3- CDC Factsheet: Salmonella pdf icon[1.38 MB]

Why Nut Pasteurizing

The unfortunate reality is that certain organisms, such as salmonella, can survive on the surface of a nut for an extended period of time in a dormant state and in fact, recent studies indicate the low moisture conditions actually strengthen the heat resistance and persistence of these organisms.

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Of the many steam-based technologies currently available, the emerging leader in nut pasteurization is the Laitram Machinery CoolSteam System.  For many years we have been leading innovators and suppliers of thermal processing systems specifically designed for delicate products such as Seafood, a variety of Vegetables, and Tree Nuts.  The technology combines the benefits of CoolSteam heating with the power of forced convection and excellent moisture management capability. 

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CoolSteam® Users
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