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Fermented Milk Products

Read pages 44-51 Fresh Fermented Milks and Creams in Harold McGee’s On Food and Cooking and answer the following questions

  1. Explain how milk “invites its own preservation”

Milk can spontaneously foster a particular group of microbes that convert its sugar into acid, and thereby preserving it for some time from spoiling or harboring disease. At the same time, the microbes also change the milk’s texture and flavor in desirable ways. This transformation, or fermentation doesn’t happen all the time but it happens enough that it has become important to people all around the world. Yogurt and sour cream are both examples of this type of transformation.

  1. Explain the role of lactic acid bacteria in milk fermentation

Lactic acid is a broken down version of lactose. When lactic acid is released into the milk it accumulates and retards the growth of most other microbes, including those that sauce human disease. This also causes the casein proteins in milk to gather together in a semisolid curds that thicken the milk.

  1. Define the following

Yogurt- is a word of Turkish decent meaning milk that has been fermented into a tart, semisolid mass.

Buttermilk- True butter milk is the low fat portion of mild or cream remaining after it has been churned to make butter. Traditionally, that milk or cream would have started to ferment  before churning and afterwards the buttermilk would continue to thicken and develop flavor.

Sour creamSour cream is a leaner, firmer, less versatile version of crème fraiche, which will curdle if applied to heat.

Crème fraiche-Is a versatile preparation, which is thick tart and has a delicately nutty or buttery aroma. Because of its higher fat content and correspondingly low protein content it can be cooked in a sauce or even boiled down without curdling


  1. What does heating the milk due in the yogurt making process?

This helps concentrate the proteins and give a firmer texture, and would be boiled for 30 minutes at 185 or at 195 for 10 minutes. These treatments improve the consistency of the yogurt by denaturing the whey protein lactoglobulin. When this happens it causes the casein particles to bond only in select spots so they create more of a chain of matrixes that is much better at retaining liquid in its small interstices.

  1. What role does powdered milk play?

Dry powdered milk can boost protein content in milk to make yogurts thicker.

  1. Why is it important for “yogurt” fermentation not to occur to swiftly?

Slow gelling of the proteins produce a finer, more delicate, more intricately network whose individual strands are weaker but whose smaller pores are better at retaining the whey. This is also the difference between yogurt that weeps its whey and one that stay’s think given time.

  1. What is the difference between crème fraiche and sour cream?

Sour cream is a leaner, firmer, less versatile version of crème fraiche, which will curdle if applied to heat. Cream Fraiche has about 30% fat content where sour cream is only about 20%

  1. What is the shelf life of crème fraiche?

Liquid crème fraiche has a refrigerator shelf life of about 15 days, but it thick counterpart because of going through fermentation can last up to 30 days.


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