Sour cream (sometimes known as soured cream in British English) is a dairy product obtained by fermenting regular cream with certain kinds of lactic acid bacteria. [1] The bacterial culture, which is introduced either deliberately or naturally, sours and thickens the cream. Its name comes from the production of lactic acid by bacterial fermentation, which is called souring. Crème fraîche is one type of sour cream with a high fat content and less sour taste.
Traditionally, sour cream was made by letting cream that was skimmed off the top of milk ferment at a moderate temperature. It can also be prepared by the souring of pasteurized cream with acid-producing bacterial culture. [2] The bacteria that developed during fermentation thickened the cream and made it more acidic, a natural way of preserving it. [3]
 | The examples and perspective in this section deal primarily with the United States and Canada and do not represent a worldwide view of the subject.(October 2021) |
According to US (FDA) regulations, commercially produced sour cream contains no less than 18% milkfat before bulking agents are added, and no less than 14.4% milkfat in the finished product. Additionally, it must have a total acidity of no less than 0.5%. [4] It may also contain milk and whey solids, buttermilk, starch in an amount not exceeding one percent, salt, and rennet derived from aqueous extracts from the fourth stomach of calves, kids or lambs, in an amount consistent with good manufacturing practice. [2] In addition, according to the Canadian food regulations, the emulsifying, gelling, stabilizing and thickening agents in sour cream are algin, carob bean gum (locust bean gum), carrageenan, gelatin, guar gum, pectin, or propylene glycol alginate or any combination thereof in an amount not exceeding 0.5 percent, [2] monoglycerides, mono- and diglycerides, or any combination thereof, in an amount not exceeding 0.3 percent, and sodium phosphate dibasic in an amount not exceeding 0.05 percent. [2]
Sour cream is not fully fermented, and like many dairy products, must be refrigerated both before and after opening the sealed container. Additionally, in Canadian regulations, a milk-coagulating enzyme derived from Rhizomucor miehei (Cooney and Emerson) from Mucor pusillus Lindt by pure culture fermentation process or from Aspergillus oryzae RET-1 (pBoel777) can also be added into sour cream production process, in an amount consistent with good manufacturing practice. [2] Sour cream is sold with an expiration date stamped on the container, though whether this is a "sell by", a "best by" or a "use by" date varies with local regulation. Refrigerated unopened sour cream can last for 1–2 weeks beyond its sell by date. Once it has been opened, refrigerated sour cream generally lasts for 7–10 days. [5]
Cultured cream. [6]
Processed sour cream can include any of the following additives and preservatives: grade A whey, modified food starch, sodium phosphate, sodium citrate, guar gum, carrageenan, calcium sulfate, potassium sorbate, and locust bean gum. [7]
The manufacturing of sour cream begins with the standardization of fat content; this step is to ensure that the desired or legal amount of milk fat is present. As previously mentioned the minimum amount of milk fat that must be present in sour cream is 18%. [8] During this step in the manufacturing process, other dry ingredients are added to the cream, such as additional whey. Another additive used during this processing step is a series of ingredients known as stabilizers. The common stabilizers that are added to sour cream are polysaccharides and gelatin, including modified food starch, guar gum, and carrageenans. Stabilizers provide a smoother texture, create specific gel structures, and reduce whey syneresis. This extends the product's shelf life. [9] Synresis can occur during the transportation, when sour cream containers are jostled and agitated. [10] The next step in the manufacturing process is acidification. Organic acids, such as citric acid or sodium citrate, are added to the cream prior to homogenization. This increases the metabolic activity of the starter culture. [9] Manufacturers heat the mixture for a short period of time to prepare it for homogenization.
Homogenization improves the quality of the sour cream in regards to color, consistency, creaming stability, and creaminess. [11] During homogenization, larger fat globules within the cream are broken down into smaller sized globules to allow an even suspension within the system. [11] At this point in the processing, the milk fat globules and the casein proteins do not interact with each other. The formation of the small globules (below 2 microns in size) increases the product's viscosity. There is also a reduction in the separation of whey, enhancing the white color of the sour cream. [12]
After homogenization of the cream, the mixture must undergo pasteurization. Pasteurization is a mild heat treatment of the cream, with the purpose of killing any harmful bacteria in the cream. The homogenized cream undergoes high temperature short time (HTST) pasteurization method. In this type of pasteurization the cream is heated to the high temperature of 85 °C for thirty minutes. This processing step creates a sterile medium in which the starter bacteria can thrive. [9]
After pasteurization, the mixture is cooled down to a temperature of 20˚C, an ideal temperature for mesophilic inoculation. It is then inoculated with 1-2% active starter culture. The starter culture initiates the fermentation process by enabling the homogenized cream to reach a pH of 4.5 to 4.8. Lactic acid bacteria (LAB) ferment lactose to lactic acid. Different LABs affect texture, aroma, and flavors, such as diacetyl. [13] [14] [15]
After inoculation the cream is portioned in packages and fermented for 18 hours, lowering the pH from about 6.5 to 4.6. After fermentation, one more cooling process takes place. After this cooling process, the sour cream is packaged into final containers and sent to market. [9]
During the pasteurization process, the temperature is raised past the point where all the particles in the system are stable. When cream is heated to temperatures above 70 °C, there is denaturation of whey proteins. To avoid phase separation brought on by the increased surface area, the fat globules readily bind with the denatured β-lactoglobulin. The adsorption of the denatured whey proteins (and whey proteins that bound with casein micelles) increases the number of structural components in the product; the texture of sour cream can be partly attributed to this. [12] [16] The denaturation of whey proteins is also known for increasing the strength of the cross-linking within the cream system, due to the formation of whey protein polymers. [17]
When the cream is inoculated with starter bacteria and the bacteria begin converting lactose to lactic acid, the pH begins a slow decrease. When this decrease begins, dissolution of calcium phosphate occurs, and causes a rapid drop in the pH. During fermentation the pH drops from around 6.5 to 4.6, this drop in pH brings on a physicochemical change to the casein micelles. Recall the casein proteins are heat stable, but they are not stable in certain acidic conditions. The colloidal particles are stable at the normal pH of milk which is 6.5-6.7, the micelles will precipitate at the isoelectric point (pI) of milk which is a pH of 4.6. At a pH of 6.5 the casein micelles repulse each other due to the electronegativity of the outer layer of the micelle. [18] During this drop in pH there is a reduction in zeta potential, from the highly net negative charges in cream to no net charge when approaching the pI. The formula shown is the Henry's equation, where z: zeta potential, Ue: electrophoretic mobility, ε: dielectric constant, η: viscosity, and f(ka): Henry's function. This equation is used to find the zeta potential, which is calculated to find the electrokinetic potential in colloidal dispersions. [19] Through electrostatic interactions the casein molecules begin approaching and aggregating together. The casein proteins enter a more ordered system, attributing to a strong gel structure formation. The whey proteins that were denatured in the heating steps of processing, are insoluble at this acidic pH and are precipitated with casein. [9] [12] [20]
The interactions involved in gelation and aggregation of casein micelles are hydrogen bonds, hydrophobic interactions, electrostatic attractions and van der Waals attractions [21] These interactions are highly dependent on pH, temperature and time. [22] At the isoelectric point, the net surface charge of casein micelle is zero and a minimum of electrostatic repulsion can be expected. [23] Furthermore, aggregation is taking place due to dominating hydrophobic interactions. Differences in the zeta potential of milk can be caused by differences in ionic strength differences, which in turn depend on the amount of calcium present in the milk. [24] The stability of milk is largely due to the electrostatic repulsion of casein micelles. These casein micelles aggregated and precipitated when they approach the absolute zeta potential values at pH 4.0 – 4.5. [25] When the heat treated and denatured, whey protein is covering the casein micelle, isoelectric point of the micelle elevated to the isoelectric point of β lactoglobulin (approximately pH 5.3). [26]
Sour cream exhibits time-dependent thixotropic behaviors. Thixotropic fluids reduce in viscosity as work is applied, and when the product is no longer under stress, the fluid returns to its previous viscosity. The viscosity of sour cream at room temperature is 100,000 cP, (for comparison: water has a viscosity of 1 cP at 20 °C). [27] The thixotropic properties exhibited by sour cream are what make it such a versatile product in the food industry.
Sour cream is commonly used as a condiment on foods, or combined with other ingredients to form a dipping sauce. It can be added to soups and sauces to help thicken and make them creamy, or in baking to help increase the moisture level over and above using milk.
In Tex–Mex cuisine, it is often used as a substitute for crema in nachos, tacos, burritos, and taquitos. [28]
Dairy products or milk products, also known as lacticinia, are food products made from milk. The most common dairy animals are cow, water buffalo, nanny goat, and ewe. Dairy products include common grocery store food around the world such as yogurt, cheese, milk and butter. A facility that produces dairy products is a dairy. Dairy products are consumed worldwide to varying degrees. Some people avoid some or all dairy products because of lactose intolerance, veganism, environmental concerns, other health reasons or beliefs.
Milk is a white liquid food produced by the mammary glands of mammals and the caecilian Siphonops annulatus. It is the primary source of nutrition for young mammals before they are able to digest solid food. Immune factors and immune-modulating components in milk contribute to milk immunity. Early-lactation milk, which is called colostrum, contains antibodies that strengthen the immune system and thus reduce the risk of many diseases. Milk contains many nutrients, including calcium and protein, but also lactose and saturated fat.
Rennet is a complex set of enzymes produced in the stomachs of ruminant mammals. Chymosin, its key component, is a protease enzyme that curdles the casein in milk. In addition to chymosin, rennet contains other enzymes, such as pepsin and a lipase.
Butter is a dairy product made from the fat and protein components of churned cream. It is a semi-solid emulsion at room temperature, consisting of approximately 80% butterfat. It is used at room temperature as a spread, melted as a condiment, and used as a fat in baking, sauce-making, pan frying, and other cooking procedures.
Yogurt is a food produced by bacterial fermentation of milk. Fermentation of sugars in the milk by these bacteria produces lactic acid, which acts on milk protein to give yogurt its texture and characteristic tart flavor. Cow's milk is most commonly used to make yogurt. Milk from water buffalo, goats, ewes, mares, camels, and yaks is also used to produce yogurt. The milk used may be homogenized or not. It may be pasteurized or raw. Each type of milk produces substantially different results.
Whey is the liquid remaining after milk has been curdled and strained. It is a byproduct of the manufacturing of cheese or casein and has several commercial uses. Sweet whey is a byproduct resulting from the manufacture of rennet types of hard cheese, like cheddar or Swiss cheese. Acid whey is a byproduct brought out during the making of acid types of dairy products, such as strained yogurt.
Cottage cheese is a curdled milk product with a mild flavour and a creamy, heterogeneous, soupy texture, made from skimmed milk. An essential step in the manufacturing process distinguishing cottage cheese from other fresh cheeses is the addition of a "dressing" to the curd grains, usually cream, which is mainly responsible for the taste of the product. Cottage cheese is not aged.
Curd is obtained by coagulating milk in a sequential process called curdling. It can be a final dairy product or the first stage in cheesemaking. The coagulation can be caused by adding rennet, a culture, or any edible acidic substance such as lemon juice or vinegar, and then allowing it to coagulate. The increased acidity causes the milk proteins (casein) to tangle into solid masses, or curds. Milk that has been left to sour will also naturally produce curds, and sour milk cheeses are produced this way.
Buttermilk is a fermented dairy drink. Traditionally, it was the liquid left behind after churning butter out of cultured cream. As most modern butter in western countries is not made with cultured cream but uncultured sweet cream, most modern buttermilk in western countries is cultured separately. It is common in warm climates where unrefrigerated milk sours quickly.
Cream cheese is a soft, usually mild-tasting fresh cheese made from milk and cream. Cream cheese is not naturally matured and is meant to be consumed fresh, so it differs from other soft cheeses such as Brie and Neufchâtel. It is more comparable in taste, texture, and production methods to Boursin and mascarpone. Stabilizers such as carob bean gum and carrageenan are often added in industrial production.
Cheesemaking is the craft of making cheese. The production of cheese, like many other food preservation processes, allows the nutritional and economic value of a food material, in this case milk, to be preserved in concentrated form. Cheesemaking allows the production of the cheese with diverse flavors and consistencies.
Blue cheese is any of a wide range of cheeses made with the addition of cultures of edible molds, which create blue-green spots or veins through the cheese. Blue cheeses vary in taste from very mild to strong, and from slightly sweet to salty or sharp; in colour from pale to dark; and in consistency from liquid or very soft to firm or hard. They may have a distinctive smell, either from the mold or from various specially cultivated bacteria such as Brevibacterium linens.
Acid-set or sour milk cheese is cheese that has been curdled (coagulated) by natural souring, often from lactic acid bacteria, or by the addition of acid. This type of cheese is technologically simple to produce.
Crème fraîche is a dairy product, a soured cream containing 10–45% butterfat, with a pH of approximately 4.5. It is soured with a bacterial culture. European labeling regulations specify the two ingredients must be cream and bacterial culture. It is served over fruit and baked goods, as well as being added to soups and sauces. It is used in a variety of other recipes. Sour cream is a similar foodstuff, except that crème fraîche is less sour and has a higher fat content. Sour cream may contain thickening agents not permitted in crème fraîche in many jurisdictions.
Skyr is a traditional Icelandic cultured dairy product. It has the consistency of strained yogurt, but a milder flavor. Skyr can be classified as a fresh sour milk cheese, similar to curd cheese consumed like a yogurt in the Baltic states, the Low Countries and Germany. It has been a part of Icelandic cuisine for centuries.
Viili (Finnish) is a mesophilic fermented milk product found in the Nordic countries, particularly Finland. Viili is similar to yoghurt or kefir, but when left unmixed, its texture is malleable, or "long". The metabolism of the bacteria used in the fermentation also gives viili a slightly different taste.
Easy Cheese is the trademark for a processed cheese spread product distributed by Mondelēz International. It is also commonly referred to by generic terms such as "spray cheese", "squirt cheese" or "cheese in a can". Easy Cheese is packaged in a metal can filled with air covered with a plastic cap that reveals a straight, flexible nozzle where the cheese is extruded.
The United States raw milk debate concerns issues of food safety and claimed health benefits of raw milk, and whether authorities responsible for regulating food safety should prohibit sale of raw milk for consumption.
Ymer is a Danish soured milk product with 6 percent protein. Compared to standard yogurt, it has a thicker, creamier consistency and a higher protein content. It has a slightly buttery taste and may be very subtly fizzy due to slight carbonation from the lactic fermentation. It was launched commercially in the 1930s. It is made by fermenting whole milk with the bacterial culture Lactococcus lactis.
Quark or quarg is a type of fresh dairy product made from milk. The milk is soured, usually by adding lactic acid bacteria cultures, and strained once the desired curdling is achieved. It can be classified as fresh acid-set cheese. Traditional quark can be made without rennet, but in modern dairies small quantities of rennet are typically added. It is soft, white and unaged, and usually has no salt added.
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