Agricultural biotech Ceres Inc. said Monday that it has completed a secondary stock offering totaling $23 million. The Thousand Oaks company sold 20 million shares at a price of $1 per share. Aegis Capital Corp. of New York, the sole book runner, exercised its option to purchase an additional 3 million shares. The company said the proceeds from the offering, after deducting underwriting discounts and commissions, will be used for general corporate purposes, including working capital. The stock has tumbled more than 21 percent since the company announced the offering last week. Ceres has been attempting to penetrate the Brazilian ethanol market for several years. The company’s genetically engineered sweet sorghum crop converts into ethanol, but breaking into the market dominated by sugar cane farmers and mills has proven difficult. The company has yet to turn a profit since going public in February 2012. Shares closed down 2 cents to $1.05 on the Nasdaq.