Explaining Moisture Flash Off

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During the high-shear, dry extrusion process, a lot of events occur at the same time.  The intense shear and pressure mechanically process the product to enhance several characteristics.  The extruder has many purposes, one of which being dehydration.  It is because of this phenomenon that antinutritional factors are deactivated, like in the case of soy processing.  A question to ask, however, is why does this occur?

The high-shear dry extruder is a unique machine.  Thermal processing occurs by friction alone.  Within the extruder, the product is put under extreme conditions, but only for a very short amount of time.  The short duration keeps nutrient availability high.  Within this retention time, the product not only undergoes intense shearing, but intense pressures as well.  Using pressure transducers, we’ve been able to measure this pressure to be several times greater than atmospheric pressure.  This compression increases as the product travels through the barrel, eventually reaching the discharge end and exiting the nose cone.  It is at this interface where physics takes over and a truly unique process happens.

It is known that water will boil at 100 degree Celsius (212 Fahrenheit) under standard atmospheric conditions (i.e. the regular air pressure you experience daily).  When water is placed under pressure, the temperature at which water boils increases.  The inverse is also true.  This explains why water will boil at a lower temperature at higher elevations since atmospheric pressure is less.  As mentioned, the environment inside the extruder barrel is under intense pressure.  There is a barrier where extruded product will go from the intense pressure into the regular atmosphere and it’s at nose cone.  The nose cone discharges into atmospheric conditions, which is a massive pressure drop.  Much like what scuba divers experience when diving to extreme depths (and the reason they need to slowly swim back to the surface to avoid decompression sickness), the extruded product experiences a similar phenomenon at a cellular level.  This massive pressure drop causes cell structures to explode, making certain aspects more bioavailable.  At the same time, the water which was under extreme pressure releases from the product, essentially “boiling” off, which is what you see in the form of steam.

The high-shear, dry extruder is a unique piece of equipment.  Dehydration is just one of the many benefits of processing through this type of extruder.  Harnessing this and other unique characteristics will enhance products you wish to process.

Please reach out to our engineering team if you have any questions.

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