AGAR AND RELATED PHYCOCOLLOIDS 67 



no final separation of free water. In the case of agar, however, full hydration or 

 the formation of a colloidal solution occurs only when the temperature is 176° F 

 (80° C), or more. Thus, when agar ice is melted, most of the water involved in 

 the solution runs oflF. Only that amount (approximately) is held by the agar which 

 dry agar would absorb if soaked to a state of equilibrium in cold water. With 

 an agar gel of one to two per cent concentration 70 to 80 per cent of the water 

 is lost in freezing and thawing. With this water, as it runs off, go 70 to 80 per cent 



(.Cou>tesy Japan Agar Dtst>ibutio}i Control Co.) 



Fig. 5-11. According to the time-honored Japanese method, agar strips which 

 have frozen are thawed and partially dehydrated and allowed to dry in the sun. 



of the soluble salts and pigments that were in the original agar solution. Thus, 

 freezing and thawing are the most efficient means of purification and dehydration, 

 especially since both results are accomplished simultaneously. With Irish moss and 

 other soft-gel seaweed extractives most of the water is reabsorbed as melting oc- 

 curs so that freezing is not feasible. All degrees of water loss, from to 80 per cent, 

 are to be found among various phycocolloids when frozen and thawed. 



Yield. The yield of finished products from seaweeds is almost always expressed 

 as a percentage of the air-dry weight of the raw material. The raw material 

 usually contains from 10 to 20 per cent moisture when it is ready for processing. 

 Different species of seaweeds yield different amounts of phycocoUoid. In general 

 those that produce a soft gel yield considerably higher than those that produce 

 agar of high gel strength. The range of commercially used species runs from 15 

 to 80 per cent, or more. In the case of Gloiopeltis, from which "funori" and sizing 

 is made, the raw material is almost completely phycocoUoid, except for its moisture 

 content. The yield of Japan's principal agar source, Gelidium amansii, ranges 

 from about 20 to 35 per cent. Part of this rather wide range arises from the 

 seasonal variation in agar content and part from the efficiency of extraction in 

 the process used. Where a yield of 45 per cent is obtained by a careful laboratory 

 analysis of a raw material sample, the factory yield of the same material may 

 be only 25 per cent, sometimes less. A commercial process never extracts all the 



