Figure 4-7. Manufacture of sour cream.
need to add additional nonfat dry milk, as for yogurt and buttermilk, since achieving a firm gel and thick body is not an issue for these high-solids products. For the same reason, the cream is pasteurized at more typical time and temperature conditions (85 °C for twenty-five seconds). However, the cream must be homogenized (usually twice) to produce a smooth-textured product with good viscosity.After the mix is cooled, the sour cream culture is added. The culture, containing mesophilic acid-producing, flavor-producing, and body-forming strains, is often the same as that is used for cultured buttermilk. The mix is then either filled into cups and incubated or incubated directly in vats (analogous to the two styles of yogurt). Incubation is at 20°C to 25°C for ten to sixteen hours. When the pH reaches about 4.4 to 4.6 (about 0.7% to 0.9% lactic acid),the sour cream is cooled, either by moving the cup-fermented product into coolers or, in the case of vat-fermented product, by stirring the product in jacket-cooled vats.The product is then pumped into containers.Sour cream should have a similar flavor profile as cultured buttermilk, with lactic acid and diacetyl predominating. Body characteristics are especially important, and various gums and other stabilizing agents are frequently added to the mix. Some manufacturers even add a small amount of chymosin to provide additional firmness. When defects do occur, they are often due to poor quality ingredients and post-pasteurization contamination by acid-tolerant yeasts and molds and psy-chrotrophic bacteria.
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