Excerpted from the Encyclopedia of New York City, Edited by Kenneth T. Jackson, Yale University Press, New Haven and London, the New-York Historical Society, New York

The production of matzo in New York City expanded rapidly during an influx of Jewish immigrants between 1880 and 1920. Most matzo bakeries were on the Lower East Side, including that of Horowitz brothers and Margareten, which had factories on East 4th Street, Meyer London's Matzos Bakery on Bayard Street, and the Finsilver Matzoh Baking Company on Pitt Street. Soon the slaughtering and meatpacking industry in the city also expanded to accommodate a rising demand for kosher meat. The wholesale value of kosher food increased 70 percent between 1900 and 1909, and by 1916 kosher meat retailers in the city had $50 million in sales. The number of butcher shops selling kosher meat increased from 1,500 in 1902 to 7,500 in 1930. Some of the largest kosher butchers and meat wholesalers were the firms of Isaac Gellis on Essex Street and S. Ershowsky and Brothers on East Houston Street. By 1934 there were about twelve thousand kosher food processors and dealers, with annual sales of more than $200 million.

The Kosher Meat Riots
Because demand for kosher food was sudden and large, kosher certification remained problematic for decades. The first efforts at regulation were made at the turn of the century by Rabbi Jacob Joseph of the Association of the United Hebrew Congregation. Later efforts continued to provoke controversy, including those of the New York Kehillah between 1910 and 1920, the Union of the Orthodox Jewish Congregations in the 1920s, and the Kashruth Association in the 1930s. Disputes over the cost of kosher meat resulted in several "kosher meat riots." The most severe occurred in May 1902 when butchers in the city closed their shops after packers raised the price of kosher meat. A settlement was reached but many customers still considered prices too high and organized a citywide boycott. Although this led to lower prices, similar incidents took place in 1910, 1929 and 1937.