66 



MARINE PRODUCTS OF COMMERCE 



wood is buined. When the water again comes to a boil, sufficient sulfuric acid is 

 added to bring the pH just to the acid side of neutrality (about 6.0). After an 

 hour or two of boiling those seaweeds which yield soft gels are added to the mix- 

 ture and the batch is simmered for another 12 hours. 



Japanese producers emphasize the importance of certain mixtures (Table 13) 

 of seaweeds for obtaining a high quality agar. The fact that American factories 

 obtain unexcelled agar by using pure Gelidittm cartiJagineum in California and 



(.Courtesy Japan Agar Distribution Control Co.) 



Fig. 5-10. In Japan agar which has been allowed to gel in wooden 

 trays is cut into bars and placed outside to freeze. 



Grdcilaria confervoides or G. foliifera (except for inadvertent contaminating 

 species) in North Carolina indicates that the Japanese add other species because 

 they are cheaper, or because the resulting gel has qualities desired for use as a 

 food. Since the admixture of soft gel species reduces gel strength and probably 

 increases elasticity, the resulting product is probably less suitable for bacteriologi- 

 cal and certain industrial uses than agar from pure Gelidiurn amansii. 



When cooking is finished, the solution from a second extraction of a previous 

 batch is added. As the solution cools, the seaweed residue slowly settles, and the 

 liquid is dipped off the top and poured into straining tanks that have perforated 

 bottoms and are lined with a straining cloth having about 20 meshes per linear 

 inch. The filtered liquid runs into a collection tank from which it is again dipped 

 and poured into shallow wooden trays, holding 14 liters each, to solidify. A rake- 

 type knife is used to cut the gel into bars. These bars are then placed outdoors 

 to freeze and thaw. In some cases the bars are first pushed through a screen 

 which cuts the agar into square straws. These, when dry, form the familiar strip 

 or shredded agar. 



When hydrophilic colloids are subjected to freezing temperatures, the force 

 of hydration is broken. The water held by the colloidal agar particles separates 

 from them in the form of ice crystals. In the case of those colloids in which 

 hydration takes place at low temperature, hydration, or reabsorption of the sepa- 

 rated water, will occur almost as fast as the ice melts and there will be little or 



