Air Date: 8-2-2013| Episode: 294
This week on IAQ Radio we talk about a subject that can be as tough to pin down as water itself. What is “water activity” and why is it important? We learn the answer today with Brad Carter, Lead Research Scientist for Decagon Devices…
This week on IAQ Radio we talk about a subject that can be as tough to pin down as water itself. What is “water activity” and why is it important? We learn the answer today with Brad Carter, Lead Research Scientist for Decagon Devices. Mr. Carter is Lead Research Scientist at Decagon Devices, Inc. He provides scientific, application, and technical support to customers. In addition, he overseas product/technology development and testing in the area of complete moisture analysis. Prior to his work at Decagon, he was an Assistant Professor/Scientist at Washington State University in Wheat Quality Research. Mr. Carter graduated Suma Cum Laude from Weber State University in 1997 with a Bachelor’s degree in Botany and Chemistry and received his Master’s degree in Cereal Chemistry from Washington State University in 1999.
Mr. Carter has written numerous journal articles, trade journals, and application notes about water activity and its importance in determining product quality and stability. He has pioneered work on determining glass transitions using dynamic isotherms. He has given numerous presentations about water activity, moisture sorption isotherms, and complete moisture analysis at professional meetings and venues around the world.
Brady Carter, a foods scientist and lead researcher at Decagon Devices, Inc. gave the hosts and listeners of IAQradio much to think about. Decagon develops, manufactures and markets devices which measure and monitor water activity among other parameters. Decagon has developed sensors which can measure, transmit and record water activity readings, a new concept for structural drying and building environmental control management.
Nuggets mined from today’s episode:
Water activity originates in the 2nd law of thermodynamics, conservation of energy and the measurement of how fast water escapes from a material. Water activity measures the energy of water inside a material not the quantity of water. Water activity is very important and most widely accepted in the food industry because potential hazardous foods over time can support the growth of pathogenic microorganisms. Water activity >.70 aw is where fungal growth usually starts. As water activity increase the number and type of competing microorganism also increases.
Polar molecules- like to react with water. For example, salt has long been known to be an effective preservative for certain types of food. Moisture becomes bound to compounds within a material.
Bound water- has no scientific meaning.
Relative humidity within a room is not the RH at the surface of wet materials.
Vapor pressure is the pressure exerted by water molecules in a confined head space. A state of Equilibrium is attained when no further net changes occur.
The speed at which fungi will grow on building materials is condition dependent. When no or few hurdles exist growth can occur quickly within 24-48 hours.
Hazard analysis and critical control points, or HACCP is a systematic preventive approach to food safety food and allergenic, chemical and biological hazards in production processes that can cause the finished product to be unsafe, and designs measurements to reduce these risks to a safe level
Hurdle concept of HACCP’s combining effects to keep microorganisms under control.
Lyse- cells coming apart due to excessive presence of moisture or other factors.
Moisture Sorption Isotherms- The relationship between water activity and moisture content at a given temperature is called the moisture sorption isotherm. This relationship is complex and unique for each product due to different interactions (colligative, capillary, and surface effects) between the water and the solid components at different moisture contents. An increase in aw is almost always accompanied by an increase in the water content, but in a nonlinear fashion. Moisture sorption isotherms are sigmoidal in shape for most foods, although foods that contain large amounts of sugar or small soluble molecules have a J-type isotherm curve shape. There is a difference (called hysteresis) in the adsorption (wetting) and desorption (drying) isotherm curves.
Steady state aka equilibrium
Wetting up- Absorption aka wetting up
I wonder if industry wide we over extending structural drying periods unnecessarily? As water activity is the primary determining factor for microbial growth, perhaps the point at which the structural drying may be considered complete is when the water activity of the wetted vulnerable materials reaches equilibrium with the environment? Can the restoration industry harness the Hurdle Concept of controlling microbial growth?
Today’s music: “We’re Gonna Move” by Elvis Pressley
Z-Man signing off