Hello, peeps! It's been a week since my last post. Now, I want to share with all of you about food preservation.
There are two techniques of food preservation based
on the temperature. The first one is using heat to kill bacteria while the
other is using cold to prevent the growth of micro-organism. The technique
which uses heat to preserve food is divided into two types. There are
pasteurization and sterilization. The purpose of pasteurization is only to
eliminate pathogenic microorganisms. Pasteurization is usually done at 60o
– 105o in Celsius. Unlike pasteurization, sterilization is intended
to kill all forms of micro-organisms inside foods. Sterilization is done at an
extremely high temperature so that no more microbes or viruses could stay
alive, as a result, food could last longer. Generally, pasteurization is used
in producing fresh milk, while sterilization is used in producing canned food.
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| http://www.cs.montana.edu |
The microbial growth curve in foods is divided into
five distinct phases.
- Lag Phase
When microbes
are introduced into new medium, they take some time to adapt in their new environment,
until they’re capable of doing ferment.
- Acceleration Phase
In this
phase, microbes have fully adapted and they‘re starting to replicate themselves,
so the number of microbes are slowly growing.
- Growth Phase
This phase sometimes
called logarithmic or exponential phase because the rate of growth number
plotting the natural logarithm of microbe number against time in a straight
line. During this phase, the replication will continue at a constant rate so
both the number of microbes and the rate of population increase doubles in each
period of time.
- Stationary Phase
As the numbers
of microbes are increasing, the nutrients inside medium are decreasing. As a
result, the rate of microbes’ growth and death are equal.
- Death Phase
At death
phase microbes are died, due to the lack of nutrients, an extreme temperature,
or alcohol level that is too high for living condition.
Every
fermentation pass through two kind of metabolism.
1.
Primary metabolism is occurs between the acceleration
and the growth phase, using energy inside the medium to replicate or reproduce.
2.
Secondary metabolism is occurs in stationary
phase. In this kind of metabolism, microbe is producing other compounds.
For an
example, in producing wine, we are using yeast fermentation. The first thing to
do is crush and squeeze the fruit (in this case is grape) until it releases its
juice, then add enough yeast and stir the mixture. This step called starter which is the first phase in microbial growth curve. Then
leave the mixture for about a week. In this period of time, the microbe will
grow following the curve and will produce alcohol as the other compound. In death
phase, the alcohol level will reach its maximum which about 8-12%. If you want
to produce wine with higher level of alcohol, you need to fortify the wine. To
fortify the wine, you need to do these three following steps. First, take the
first half of the wine, left the other half. Second, you need to distill the first
half of the wine until you obtain the pure 100% alcohol. Lastly, put the pure
alcohol into the other half of the wine. Now you have wine with higher level of
alcohol. After that, you need to leave the wine for aging at least a month. Aging
is needed to get the exact color and flavor of the wine as we wanted. During
this step, we could see pulps begin to form. You could remove the pulp before you
bottle the wine. Use bottle or barrel which made from wood to prevent any
unwanted changes.
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| http://www.bbc.co.uk |
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| http://www.bbc.co.uk |
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| http://www.bbc.co.uk |
There is another way of fermentation using enzyme instead of microbe. The principle is not much of a different, that enzyme also cannot work in an extreme temperature. Browning apples is only one of the examples of the enzyme inside food. To prevent food from browning, we could put the food inside salty water or blanch the food.
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