factories a decade earlier. In the late 1870s, the centrifugal cream separator was introduced, marketed most successfully by Swedish engineer Carl Gustaf Patrik de Laval. In 1920, Otto Hunziker authored The Butter Industry, Prepared for Factory, School and Laboratory, a well-known text in the industry that enjoyed at least three editions (1920, 1927, 1940). As part of the efforts of the American Dairy Science Association, Professor Hunziker and others published articles regarding: causes of tallowiness (an odor defect, distinct from rancidity, a taste defect); mottles (an aesthetic issue related to uneven color); introduced salts; the impact of creamery metals and liquids; and acidity measurement. These and other ADSA publications helped standardize practices internationally. Butter consumption declined in most western nations during the 20th century, mainly because of the rising popularity of margarine, which is less expensive and, until recent years, was perceived as being healthier. In the United States, margarine consumption overtook butter during the 1950s, and it is still the case today that more margarine than butter is eaten in the U.S. and the EU. Worldwide production In 1997, India produced of butter, most of which was consumed domestically. Second in production was the United States (), followed by France (), Germany (), and New Zealand (). France ranks first in per capita butter consumption with 8 kg per capita per year. In terms of absolute consumption, Germany was second after India, using of butter in 1997, followed by France (), Russia (), and the United States (). New Zealand, Australia, Denmark and Ukraine are among the few nations that export a significant percentage of the butter they produce. Different varieties are found around the world. Smen is a spiced Moroccan clarified butter, buried in the ground and aged for months or years. A similar product is maltash of the Hunza Valley, where cow and yak butter can be buried for decades, and is used at events such as weddings. Yak butter is a specialty in Tibet; tsampa, barley flour mixed with yak butter, is a staple food. Butter tea is consumed in the Himalayan regions of Tibet, Bhutan, Nepal and India. It consists of tea served with intensely flavored—or "rancid"—yak butter and salt. In African and Asian nations, butter is sometimes traditionally made from sour milk rather than cream. It can take several hours of churning to produce workable butter grains from fermented milk. Storage Normal butter softens