CULTURED OR SOUR CREAM PROCESSING A. Processing

1. Sour cream Ingredients

According to the CFR (Title 21, Section 131.160), sour cream must contain at least 18%

milk fat and have a titratable acidity of at least 0.5%, expressed as lactic acid (36,37).

Optional ingredients may be used to improve texture, prevent syneresis, improve flavor, or extend shelf life, but sour cream may not contain more than 0.1% sodium citrate, salt, rennet, nutritive sweeteners, flavoring, or coloring (36,37).

Production of high-quality sour cream (Fig. 6) must begin with high-quality milk and/or cream. If high viscosity is desired, or if mechanical agitation will be employed, the body may be improved by including stabilizers (hydrophilic colloids bind water), WPC, NFDM, or by using cultures that naturally excrete polysaccharides. Sour cream made with 18% fat may not need stabilizer (38). Stabilizers may be used at about 0.5%, and 0.2%

citric acid may be used for flavor and enhanced culture activity. Occasionally, particularly outside the United States, chymosin, which is used in cheesemaking to augment coagu-Table 5 Continued

Observation Explanation Solution

Weak body Weak yogurt does not stand up in the spoon, and/or may appear watery due to 1) under-stabilization, 2) low casein or low total milk solids, 3) under incubation, or 4) low pasteurization temperature.

Careful yogurt base formulation and strict control of

pasteurization temperature.

Color leaching Pigment trails or leaching of color from fruit into yogurt, caused by low pH (<3.8) or incomplete blending of yogurt base with fruit flavoring material.

Free whey Whey release from curd may be due to (1) low milk solids, (2) excess acid development, (3) agitation during

MSNF must be at least 8.25%.

Practice good overall process

Shrunken Curd pulls away from carton due to tightening of curd structure; often associated with free whey.

Practice process control measures used to prevent free whey defect.

Source: Refs. 3 and 28.

lation, is used in sour cream production (0.5 mL single-strength chymosin/38 L cream) to improve gel strength (40).

Sour cream should have a mild, subtle, aromatic, and slightly acidic flavor (1,2) composed of lactic, acetic, butanoic and carbonic acids, and diacetyl (38). Desirable sour cream is bright, has a uniform smooth structure, and is relatively viscous or firm. Excessive addition of stabilizers and/or emulsifiers may impart an overly heavy body and can detract from the delicate, desirable flavor of cultured sour cream. Masking of flavor may occur when stabilizer/emulsifier levels exceed a recommended product usage level of 0.30–0.40% (w/w) (3). Under extended storage, quality breaks down as bacterial proteolytic enzymes cleave proteins into bitter peptides (1,2). Additionally, carbon dioxide and other aromatic sub-stances can diffuse through the packages, causing off-flavor formation (1). Yeasts and molds can develop on the surface of sour cream readily if packages are not airtight. Sometimes sorbate is added to suppress the growth of yeast and mold, but since sorbate can also slow down cultures, the manufacturing procedure may need to be extended 3–4 hr (39).

Lowfat and nonfat sour cream are also available in the market. Because reduced-fat sour creams are inherently thinner than their full-fat counterparts, a combination of agar, guar gum, and carrageenan is a good mix for lower-fat versions of sour cream (38). Balance is important because excessive use of gelatin may yield a body much like Jello, and high levels of modified food starch may result in a pasty product body (38). Additionally, Figure 6 Production of sour cream.

modified food starch and/or sugar may be used to cut the harsh flavor common to reduced fat sour cream.

2. Sour Cream Processing

Typically, cream with 18–20% fat and 25–28% total milk solids is heated to 60–71jC in order to inactivate lipase prior to homogenization (Fig. 6).The cream may be preheated or completely pasteurized (either at 74–82jC for 30 min or HTST pasteurized at 85jC for 25–

60 sec or 86–88jC for 3–5 min) prior to homogenization, depending on the processing plant layout. Preheating is necessary because homogenization of raw milk will result in rancid off-flavors in sour cream. The high pasteurization temperature not only inactivates bacteria, yeasts, and molds but denatures whey proteins, which improves water-binding capacity, so the sour cream is less likely to whey off. It has been noted (38) that LTLT pasteurization produces a strong-bodied sour cream compared to HTST pasteurization.

Homogenization is done at temperatures ranging from 40jC to 85jC at a pressure of 2,000–3,000 psi (14–21 MPa, 140–210 bar) (3). Cream with low fat (10–18%) is homog-enized at 2,100–2,500 psi (15–20 MPa, 150–200 bar). However, cream with high fat (20–

30%) is homogenized at 1,500–2,000 psi (10–12 MPa, 100–120 bar) because there is not enough casein to form membranes on the enlarged total surface area of the fat globules (1).

Homogenization at higher temperatures has been shown to improve sour cream consist-ency (1). Additionally, researchers at Cornell University found that dual-homogenization (homogenizing twice) of highly heated light cream can improve sour cream smoothness and viscosity (2). A high degree of viscosity results from dual-homogenization due to ex-tensive clumping of fat globules.

After pasteurization and homogenization, cream is cooled to 21–30jC and inocu-lated with 0.5%–2% starter culture. The starter organisms utilized to make sour cream include Lactoococcus lactis subsp lactis and cremoris. Citrate + Lactococcus lactis subsp lactisand Leuconostoc citrovorum are also used for aroma (1). Lactococcus can produce acetaldehyde while Leuconostoc can use acetaldehyde, so combining the two is useful, because excessive acetaldehyde is inappropriate in sour cream. Incubation can take place in a tank or in the packages. Either way, inoculated milk is held for 16–20 hr at 20–30jC (most typically 20–22jC) or until the proper acidity (0.70–0.90) and pH (4.50–4.55) are attained (1). After coagulation, the curd is quickly cooled to 10jC, or lower, to prevent further reduction in pH. If the product is fermented in containers, no breakage of curd is necessary, and fermentation may take 16–18 hr. If sour cream is fermented in a tank, stirring, pumping, and packing cause a slight deterioration of its structure, or thinning (1).

To minimize deterioration, ice water or coolant may be introduced to the jacket of the vat or processor. The agitator should only be rotated several turns, at intermittent intervals, throughout the time required to cool the product (3). Sour cream usually keeps for 3–4 weeks and the pH is generally 4.2–4.4.

After the curd is formed, at about pH 4.5, sour cream may be packaged cold or warm. If cooled in the vat, a TA of 0.70 or a pH of 4.5 must be attained prior to agitation.

Stirred cold sour cream can be pumped from the vat through a grid insert in the pipeline into the hopper of a mechanical filler. Alternatively, the warm sour cream can be pumped through an in-line grid or an in-line homogenizing valve assembly at 170 to 690 kPa (25–

100 psi) into a packaging machine hopper. This assembly is located in the sanitary pipeline at the discharge side of a variable-capacity sanitary positive pump. The warm or cold sour cream must be packaged immediately in 114–228 g consumer containers or 2.5–4.5 kg polyethylene-lined tins (40). The containers should be cooled overnight to 3–5jC and held for 24–48 hours before distribution to observe for bloats (gas production) or other rejects.

Once containers are packed, they are transferred to a blast cooler until the temper-ature is lowered to about 5–7jC. The product can be held in a regular cooler until dis-tribution. Boxes of packaged sour cream are palletized in a circulating air chillroom to maximize the cooling rate (40).

B. Troubleshooting

Even when strict controls have been enforced, sometimes product quality suffers.Table 6 outlines some of the defects that may be found in sour cream products, their probable cause, and possible ways to prevent or avoid these defects.

V. SUMMARY

Cultured dairy products, including yogurt and sour cream, continue to gain popularity in the United States as new products appeal to consumer tastes and consumers realize the potential health benefits. Manufacturers must maintain sanitary practices, formulate ap-propriately, and process consistently, to deliver what they promise: consistent, high-quality cultured dairy products to consumers.

Table 6 Troubleshooting Guide for Sour Cream Production

Observation Explanation Solution

Too firm body Overstabilized product base. Reduce stabilizer/emulsifier to less than 0.4%. Modify processing techniques (homogenization and/or pasteurization).

Weak body (too thin) Processing techniques not optimized. Lack of

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