Milling Journal - Q3 2008 - (Page 35)

humidity line in Figure 3 (on page 34), where the first line intersects the graph; draw a horizontal line intersecting the graph’s vertical axis. This is the moisture content that will place the flour/wheat at equilibrium, with its environment at a specified temperature. It is around 14% to15%. The equilibrium moisture content of a biological product in a closed container is influenced by product composition including initial moisture content and storage temperature. At a low temperature and relative humidity, equilibrium moisture content of a product drops. Remember those raisins from last year you found in the refrigerator just before the fall baking season? A compromised seal on bread sent to Arizona will lose moisture to the environment; it will become stale, taste bad, and be rejected by the customer. Bread packaged before it is properly cooled will mould quickly due to the freely available water and the presence of yeast and mold spores. Daily Relative Humidity Differences During certain times of the year in a Midwest city, the relative humidity difference during the day (24-hour period) exceeds 20% (See Figure 4 below). The head space maximum temperature exceeds the measured outside ambient temperature, perhaps more so in the summer than in the winter. Remember the earlier car example? Daily head space temperature swings exceed ambient swings by 10 to 40 degrees, for a total of 30 to 70 degrees difference. The mean minimum temperature in our Midwestern city example is either below or within a degree of the dew point. However, in an enclosed bin where moisture has been released into the head space and the relative humidity is higher than ambient, the dew point will be higher than the ambient temperature. Moisture will condense on the bin wall. Table I (below) shows the similarity between moisture in flour transportation and storage. Table I Moisture in Flour Transportation and Storage Bins • Flour in a transportation container is challenged the same as flour in a storage bin. • Both are basically closed systems constructed of metal, in most cases. • Both systems will consist of space occupied by flour and head space above the flour. • Metal will be relatively inert in both situations in terms of taking on and giving up water. Response No. 351 MILLING JOURNAL Third Quarter 2008 35 http://www.cetec.org http://www.cetec.org

Table of Contents Feed for the Digital Edition of Milling Journal - Q3 2008

Milling Journal - Q3 2008 Contents Milling News Far West Rice Generates Own Power New IAOM-KSU Resident Courses Theodore "Ted" Korolchuk: Miller of the Year IAOM News New IGP Wheat/Flour Web Site Wheat Tempering and Surfactants New ADM Milling Center 2008-09 IAOM Officers Controlling Condensation International IAOM Meetings Pest Management/Subramanyam 2008 Wheat Crop Quality Report Product Quality/Gwirtz Buhler 2009 Resident Courses Northern U.S. Wheat/Backman Horizon Milling to Close ON Mill 2nd Quarter Milling Production Chilled Rolls Belting Product Reviews Milling News Enrichments Phil Weisenberger Obituary Material Handling Pneumatic Systems Mixers Roller Mills Roll Corrugation Product Reviews Storage Transportation Equipment Product/Service Directory Ad Index

Milling Journal - Q3 2008

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