UTF-8Chemical Reactions: Activation Energy227223152
Reaction Rates, Catalysis, and Energy: Pasteurization.
Below is a very simplified model of "milk". Milk is a complex mixture of many different molecules, and bacteria are small organisms comprised of many molecules as well. However, in this model one type of molecule will represent "the bacteria" (or just an important molecule necessary for the bacteria to live), and the other type of molecule will represent the "milk flavor".
In Pasteurization, you want to provide enough heat energy to reach the activation energy necessary to break down bacteria (or molecules necessary for bacteria to live), but leave the milk flavor unchanged. To do this, run the model, and adjust the temperature silder below so you have the best balance between low % bacteria, and high % milk flavor (see the graphs next to the model).
Helpful hint: If you click once on the slider, you can then use the arrow keys to nudge the temperature up and down.
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<font size="4" face="Verdana, Arial, Helvetica, sans-serif">For a long
time many people got sick from bacteria that were growing in milk.
Scientists found that milk could be sterilized by boiling it, but that
made the milk taste bad. However, if the milk was heated to a high enough
temperature to kill bacteria (or most of them), then the taste of the milk
could be retained, and the negative health effects from the bacteria could
be mostly eliminated. This process of heating foods to kill bacteria
without heating them enough to ruin the flavor is called <strong>Pasteurization</strong>,
after Louis Pasteur who discovered this technique in the 1860's. </font>
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<font size="4" face="Times,serif"><strong>What happens to the amount of healthy bacteria (left graph) and the milk flavor (right graph) as you slowly increase the temperature using the arrow keys (see hint above the slider)?</strong></font>
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<font size="4" face="Times,serif"><strong>If high temperatures kill bacteria, why isn't the highest possible temperature used to make milk safe?</strong></font>
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