MOOlecules of Dairy

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Dairy can be found in a variety of food products such as milk, butter, cheese and even ice cream. The chemistry behind the dairy in all these foods remains the same and can explain why you get butter when you agitate heavy cream or what makes a smooth batch of homemade ice cream.

Dairy & Chemistry

Casein: This is the major protein in milk. Casein micelles contain much of milk’s calcium due to the presence of phosphate groups. Casein is also the cause of clumps, or coagulation, when the negative charge on the phosphate group is cleaved off.

Whey: Water-soluble proteins that contain enzymes and other proteins such as lactoglobulin. Denatured lactoclobulin binds with the casein micells.

Lactose (below): “Milk sugar” is composed of two sugars, glucose and galactose. The enzyme lactase is necessary to digest lactose (many adults do not have this enzyme).


Many everyday foods, such as butter and ice cream, can be made in the home with the right ingredients and knowledge! In class we used the following recipes to make homemade butter and ice cream with liquid nitrogen.

Homemade Butter

What You Will Need: 1 Jar with lid, Heavy Cream, Water (to wash with), Strainer

What You Will Do: Pour the heavy cream into the jar, close and shake! You may want to vent the jar occasionally to prevent the build up of pressure. Once the solid butter has formed wash away the buttermilk with water and strain.

The Chemistry of What You Will See: Cream contains fat and protein in a 10 to 1 ratio. The fat globules can be easily damaged through agitation (shaking the jar) causing the fat to leak out and come together into a mass large enough to gather. After enough shaking a large solid will form (that’s the butter!) Continue a little longer and you will see a liquid (that’s buttermilk).

Fat Facts (McGee, 2004)

Product

Fat Content

Heavy Cream

36+%

Half-and-half

12%

Light Cream

20%

Whipping Cream

35+%


Homemade Ice Cream with Liquid Nitrogen

A variety of ice cream bases, listed in the table below, were prepared to compare the effects of different amounts of cream, milk, sugar and egg yolks would have. To make the ice cream we used a standing kitchen mixer and liquid nitrogen!

The Bases: Philadelphia: Made from cream, milk (scalded) and sugar it is the standard ice cream base. Raw Philadelphia: In this base the milk is not scalded. Vanilla/Chocolate: The milk and sugar were heated to 170-180°C while whisking, the cold cream was then mixed in, followed by the vanilla (and 2 oz. chocolate powder that had been carefully incorporated into the mixture). French: Similar to a custard, contains egg yolks. Gelato: Also contains egg yolks but has a higher cream content than the French base. In addition to the ingredients listed in the table all the bases had 1 ½ teaspoons of vanilla extract.

Base

Cream

Milk

Sugar

Egg Yolks

Philadelphia

2 cup

2 cup

3/4 cup

Raw Philadelphia

2 cup

2 cup

3/4 cup

Vanilla

3 cup

1 cup

1 cup

 Chocolate

3 cup

1 cup

1 cup

French

1 cup

3 cup

3/4 cup

10

Gelato

3 cup

1 cup

3/4 cup

10

Ice cream consists of ice crystals, fat and air. The air aids in making the ice cream easy to serve because it weakens the matrix of ice crystals that form from the water.

The Results: The class came to the conclusion that the chocolate was our favorite. It had delicate and smooth texture due to the slow and careful incorporation of the cocoa powder (picture left) to insure that no lumps formed. In both the raw and regular Philly we detected ice crystals that were probably due to the low level of fat content in the base. The ice cream had also melted considerably before it was put in the freezer which could also be an additional factor leading to the formation of crystals. The French and Gelato had a strong egg flavor which was not acceptable by all.


Cheese

What would be a day on dairy without cheese?

Cheese is a delicious dairy product that comes in a variety of types. The basics parts that go into making cheese are milk and rennet enzymes. Essentially, the rennet, which was originally made from the stomach of a lamb or goat, produces an enzyme called chymosin (McGee, 2004). Chymosin cleaves the negative charge tail on kappa-casein protein, which consists of phosphate-substituted amino acids. By cleaving this negative charge the casein molecules can now bond to each other and form the curd and remove the water. Now, most cheeses are made with “vegetable rennets”, with the exception of traditional European and other artisan cheeses. (Picture from squaremeal.tumblr.com)

The Cheese Process (McGee, 2004):

  1. Lactic acid bacteria converts milk sugar (lactose) into lactic acid
  2. Rennet is added causing casein proteins to bond and curd
  3. Enzymes work together to ripen the cheese

Depending on the type of cheese the process will vary at this point. For example, a feta will be placed in brine while a parmesan will be heated and pressed to release more whey.

On the Chemical Level:  In mozzarella casein particles are cross-linked into long fibers by calcium. In ricotta casein is curdled exclusively by acid which dissolves calcium glue that hold casein together.


MOOlecules of Flavor

These molecules are just a few examples of the chemistry behind the aromas and flavors you taste when you are eating or cooking. Every flavor, after all, is a result of chemistry!

 References

  1. McGee, Harold. On Food and Cooking: The Science and Lore of the Kitchen. New York: Scribner, 2004. Print.
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