The secret is in the water: Moisture vs. Water Activity
Water is a key component of food, but it does not always appear in the same form. We need to distinguish between bound water, which is chemically linked to nutrients (such as sugars or proteins), and free water, which is the fraction not held by other compounds. It is precisely this free or available water that determines the life of the food, as it is the only water that microorganisms can use to grow and multiply.
When we want to express the water content of a food, we can do it in two ways:
Moisture (water weight): Measures the total amount of water in a food, whether free or bound to other molecules. It is expressed as a percentage (%), meaning the grams of water in 100 g of food. To measure moisture in food, a thermogravimetric balance can be used.
Water Activity (aw): Measures the availability of water for microorganisms. It is measured on a scale from 0 to 1. It has no unit and is a relative value. Water activity is measured with a water activity meter.
| Water Activity Range | Food |
| 0,95-1 | Most fresh foods, such as fresh fruits and vegetables, meat, and fish. |
| 0,75-0,80 |
Candied fruits or marmalades. |
| 0,60-0,65 | Dried fruits with 15-20% moisture. |
| 0,20-0,30 | Dried vegetables. |
Technology vs. Water
The Spanish Food Code defines the treatments for reducing water content in foods, but with the effect of zero gravity, the definitions have become mixed up. Help Lili match each treatment with its correct definition.
The Spanish Food Code defines the treatments for reducing water content in foods, but with the effect of zero gravity, the definitions have become mixed up. Help Lili match each treatment with its correct definition.
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