First coffee, now this: Poor harvests combined with speculative buying have sent sugar futures soaring. Contract prices reached 15.16 cents on Nov. 28, up 37% from July. Historically, higher prices have scared off commercial buyers. But Algeria jolted the market with a huge purchase in mid-November. Now China, which, like Russia and Cuba, has had a paltry crop, is said to be buying heavily. Even with demand so robust, though, investors should beware: Sugar "usually goes down faster than it goes up," notes Smith Barney analyst Walter Spilka.