Amyris, an Emeryville, Calif.-based start-up that is developing farnesene as a building-block chemical, is pulling back on aggressive expansion plans in light of manufacturing difficulties. The company began production last year at sites run by contract manufacturers in the U.S., Spain, and Brazil. Amyris CEO John G. Melo told analysts in a Feb. 9 conference call that the Brazilian facility has “operational issues.” He said the company has learned that “it takes time to translate from the peak yield levels in the lab to maintaining those yields over longer operational periods in the field.” Amyris will not meet its stated goal of making 40 million to 50 million L of farnesene in 2012, he acknowledged. Additionally, Melo is no longer forecasting that the company will have positive cash flow in 2012. Amyris thus aims to raise money in a round of equity financing, although Melo declined to offer details. Amyris shares plunged 28% the day after his disclosure.