science

Sour cream

Sour cream is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sour cream rather than just read about it. In short: 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. The bacterial culture, which is introduced either deliberately or naturally, sours and thickens the cream.

Key takeaways

Sour cream belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sour cream to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sour cream from memory before moving on to harder problems.

Reference excerpt

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. 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.

Traditional 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. The bacteria that developed during fermentation thickened the cream and made it more acidic, a natural way of preserving it.

Commercial varieties

According to US (FDA) regulations, commercially produced sour cream contains no less than 18% milk fat before bulking agents are added, and no less than 14.4% milk fat in the finished product. Additionally, it must have a total acidity of no less than 0.5%. 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. 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, 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. Sour cream is not fully fermented, and like many dairy products, it 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 to the sour cream production process in an amount consistent with good manufacturing practice. Sour cream is sold with an expiration date stamped on the container, though whether this is a "sell by", a "best by" or "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.

Physicochemical properties

Ingredients Cultured cream. 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.

Processing 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%. 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. Synresis can occur during the transportation, when sour cream containers are jostled and agitated. 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. 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. During homogenization, larger fat globules within the cream are broken down into smaller sized globules to allow an even suspension within the system. 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. 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. 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. 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.

… excerpt ends here. Continue reading the full article.

Illustrations

Sour cream: Simple illustration of the processing order of sour cream manufacturing — Simple illustration of the processing order of sour cream manufacturing

Worked examples

Example 1 — a first encounter with Sour cream

Start with the simplest possible case. Write down what Sour cream claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sour cream before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sour cream ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sour cream

In research: Sour cream appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sour cream in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sour cream is common in secondary-school and first-year university syllabi. It links to neighbouring topics American cuisine, Australian cuisine, British cuisine, so understanding it makes those chapters shorter.
In everyday life: Look for Sour cream outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sour cream in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sour cream means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sour cream out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sour cream in simple terms?

Why does Sour cream matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sour cream?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sour cream.