The new darling on the dairy shelf is almond milk.

Two brands—Silk Pure Almond, from Dean Foods Co., of Dallas, and Almond Breeze, from Blue Diamond Growers, of Sacramento, Calif.—are waging a Coke-and-Pepsi style market-share battle in the supermarket. Almond milk's appearance in the refrigerated dairy case in 2010 helped fuel 13% growth in milk alternatives, a category where sales were flat the year before, according to SymphonyIRI Group, a Chicago market research firm.

Milk...