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Chemistry in the kitchen

May 31, 2009
By Bonnie Peck, For The Leader-Herald

One of the greatest ways to help kids continue to learn through the summer is by finding ways to incorporate what they learn in school into their every day lives.

This might mean reading a book in order to develop a new skill or find the answer to a burning question.

It might mean holding a lawn sale and adding and dividing the profits amongst those who helped.

It could even mean a trip to local historic sights and museums to learn about local history.

All of these are great ways to help children retain what they have learned in school and maybe even develop new understandings.

One of the best ways to incorporate science into the lives of children would be to examine it's role in one of a kids favorite places on earth the family kitchen.

Webster's Dictionary defines science as "such knowledge concerned with the physical world and it's phenomena."

Every time we cook a meal we are doing science.

Although we realize that baking a cake involves taking ingredients in various physical states (liquid, and various forms of solid) and transforming them into a different state altogether, kids often do not look at this as science.

However, one chemistry lesson you can do with your children that truly appeals to the scientist in them is that of making cheese.

You can make some form of cheese from any milk.

There are many recipes that require cows milk, or goats milk, or even milk from sheep.

There are endless chemistry experiments for kids in the realm of cheesemaking.

As with any chemistry lab, the kitchen must have the proper utensils, chemical ingredients, and conditions.

As with most experiments, one must follow the directions carefully in order to have consistent outcomes.

Sometimes even the slightest variation can impact the final result.

The most basic equipment needed to make the simplest variety of cheese include the following:

Glass or stainless steel measuring cup and spoons,

A dairy thermometer that accurately measures from 20 degrees to 220 degrees Farenheit.

This can be checked for accuracy by testing it in boiling water it should read 212 degree F. If not, adjustments can be made (math, anyone?) (a floating glass thermometer or stainless steel dial thermometer are best);

Pots that are stainless steel, glass or enamel lined that are large enough to hold the amount of milk you plan to work with;

A very large pot, large enough to fit the pot of milk into "double-boiler" style with water around it for indirect heating;

A stainless steel spoon and/or ladle;

Stainless steel colander;

Cheese cloth. This is not the cheap webbing that you can find at the grocery store. It should be more closely woven, almost like a loosely woven muslin.

In order to experiment with other types of cheese beyond an easy-to-make soft cheese, the list of supplies will be larger.

This list may include items such as a long stainless steel knife that can reach the bottom of the pot, butter muslin, molds, and a cheese press.

As previously noted, all the equipment needed should be either glass, stainless steel or enamel coated.

The reason for this is scientific.

During cheese making, milk becomes acidic. Aluminum and cast iron pots will release metallic salts into the curds, which will cause an undesirable flavor and may even be dangerous to eat.

As in all chemistry, there are certain ingredients that make the difference in how your "experiment" turns out.

If you were to make a very simple recipe of cheese, you would only need milk and either lemon juice or vinegar.

Lemon juice and vinegar are used for acid coagulation.

Milk can be coagulated using an acid substance, or by adding a bacterial culture which turns the lactose into lactic acid.

Both ways will produce a curd and each method involves a different procedure and will have different results.

More involved recipes would involve coagulation using cheese rennet (not to be confused with junket rennet).

Rennet can be either plant based or animal based. Animal- derived rennet is extracted from the stomach of a calf or young goat and contains an enzyme called rennin.

Plant based rennet is an enzyme that comes from the mold Mucor miehei.

Both types of rennet are available in both liquid and tablet form.

Most varieties are made incorporating different types of bacteria and molds as well as different growing "conditions."

Harder cheeses involve squeezing more of the liquid from the cheese.

Some varieties involve aging in controlled climates (specific temperature and humidity) and with injection of specific molds at different stages.

No matter what kind of cheese being made, the first and most importance factor is the environment.

All utensils must be carefully cleaned before and after making cheese.

The whole process is based on the action of friendly bacteria. If the area isn't clean and sterile you can allow "bad" bacteria to get involved in the process making the product either unsafe or unpalatable.

Utensils should be rinsed in cold water before being washed in hot soapy water. Why? The hot water on a hot ladle will "cook" the milk on, making it harder to get off.

After washing carefully, rinse with hot water.

Always wash utensils carefully just before using them as well.

For best results, sterilize all equipment. There are three ways this can be done.

First would be to immerse equipment in boiling water for at least 5 minutes.

Another option would be to Steam utensils for at least 5 minutes in a kettle with about 2 inches of water in the bottom and a tight lid on top. (Wooden items such as cheese boards and mats must be done in one of these two ways for at least 20 minutes).

A third method is to sterilize using a solution of household bleach mixed with water.

The concentration for this would be 2 tablespoons of bleach to one gallon of water. Note: this is the only way to sterilize food grade plastic, like that which many molds are made from. It is extremely important to rinse items thoroughly after using bleach. The bleach residue (sodium hypochlorite) can affect the growth of desired bacteria in your cheese.

Cheese cloth should be clean and can also be boiled or soaked in the bleach solution (be sure to rinse it well). It is best to air dry utensilsdo not use dish towelsthey usually have bacteria on them!

Wipe down clean counters with a cloth dampened by the bleach solution before beginning the activity The following is an easy recipe for "Lemon Cheese" which has only a very slight flavor of lemon. It is a moist cheese that spreads very easily. Place pot with 1 quart of milk in it into a pot of water on the stove and heat until the milk is 170 degrees F(double boiler style, this is called indirect heating). Add the juice of 2 lemons (about cup) and stir well. Let the milk stand until it sets (curds separate from whey). This should take about 15-30 minutes.

If the milk does not set, add more lemon juice.

Once it is set, pour the curds into a cheesecloth-lined colander. Tie the four corners of the cheesecloth into a knot and hang the bag to drain for 1 to 2 hours or until the curds have stopped draining.

Note: You can save the whey for use in cooking.

Take the cheese out of the cheesecloth. You may have to scrape some off the cloth.

The cheese can be lightly salted and herbs added if desired. The yield should be about 6 to 8 ounces of lemon cheese for each quart of milk.

A good experiment for kids would be to see what happens if you heat the milk more/or less, use more or less lemon juice, substitute vinegar for lemon juice, etc.

They can make predictions as to what might happen differently and then compare the outcome to that of the recipe.

4-H has a broad range of project materials that help connect science to the every day lives of youth.

For more information, contact Bonnie Peck at Cornell Cooperative Extension.



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