PURPOSE: To readily obtain an inexpensive and safe drink containing a silicate, by treating a plant of the family Equisetaceae of the class Pteridophyte with a weakly alkaline potassium salt.

CONSTITUTION: A nutrient stem of a plant of the family Equisetaceae of the class Pteridophyte is collected at 3W5 months growth period, directly dried in the shade and preserved. The resultant nurient stem is cut to about 2W10mm length, sufficiently washed with cold water and then dipped in an aqueous solution containing dissolved 1%, based on the weight of the dried material, potassium carbonate. The dipping time is normally 12W24hr. The dipped solution is then boiled to give the aimed brown extract solution for 3W5hr. The resultant extract solution has an amount of extracted silicates 3W5 times as much as that obtained without treating with the potassium carbonate solution under the same condition and the stable extract solution is obtained.