A DNA fragment derived from coffee encoding at least one enzyme involved in the hydrolysis of polysaccharides comprising pure or branched mannan molecules linked to each other via a \u03b2 linkage, and which has the the nucleic acid sequence SEQ ID NO. An internal ferrous armature attracts the magnet which provides flux holding a switch element open when the magnet provides at least a predetermined flux to the switch. A preferred polysulfide is a di-t-butyl polysulfide. The positive and negative probe is extended into the recess in contact with the sample water. The emission portion is formed to have a plurality of successive convex surfaces when seen in a cross section taken along the longitudinal direction thereof.