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Brix means "refractive index". This is used because a liquid has a different refractive index when other substances are dissolved in it. A refractometer therefore indicates a scale that indicates exactly how much of a particular substance is in the water. In practice, however, this is not so easy. This is only possible if it contains one substance that you want to measure (for example, think of only sugar in water).

In practice this works as follows: the juice from a fruit will not only consist of water and sugar. The value that is read on the refractometer is therefore not the "real" sugar content. This is because the refractive index will be "disturbed"/changed by the other dissolved substances that are also in the juice. That is why you should see it mainly as an empirical number. It is good to look at a certain trend in the brix value. This trend can be anticipated, so that products always have approximately the same value. In general, the higher the brix value, the better the quality. High brix values indicate a sweeter taste and better shelf life.

When a sugar-based liquid is measured, an actual concentration is calculated. When measuring a solution which also contains elements other than sugar, a conversion table is needed to correct the measured value and ensure that the value has been measured correctly. In general, these values are used. But it is also possible to deviate from them:

Brix-values/quality	Poor	Average	Good	Excellent
Fruits
Strawberry	8	12	16	18
Blueberry	4	8	16	22
Blackberry	6	8	12	14
Melon (Watermelon)	8	12	16	18
Grape	8	12	18	22
Raspberry	6	8	12	14
Cherry	6	8	14	16
Vegetables
Potato	3	5	7	10
Endive	4	6	10	12
Asparagus	4	6	8	10
Bell pepper	4	6	8	12
Pepper (red pepper)	4	6	8	10
Parsley	4	6	8	10
Celery	4	6	10	12
Lettuce	4	6	8	10
Tomato	4	6	10	14
Onion	4	6	10	12
Carrot	4	8	14	18

First, there are various types of refractometers. There are analog and digital refractometers. Both refractometers are described below. This is how you use an analog refractometer:

1. Open the cover and aim the refractometer with the prism towards bright light or a light source. If necessary, turn the focus ring until the scale is sharp.
2. Open the cover and wipe the prism with a soft cloth.
3. Apply a few drops of fluid to be measured to the prism. Close the cover and press lightly so that the liquid spreads over the prism without forming bubbles.
4. Hold the device horizontally and wait 30 seconds for temperature compensation to work.
5. Read the value on the dividing line between white and blue.
6. Clean and dry the prism.
   

In principle, calibration on a refractometer is not necessary. During normal use, a measurement will not shift. The same goes for maintenance. However, it is important to keep the refractometer clean. However, do not use water to clean the prism. This is to prevent water from entering the instrument. Clean the prism with a dry or slightly damp cloth. Never immerse the appliance in water or rinse it under running water.

Since the refractometer is an optical instrument, it should also be handled with care. This means that heavy shocks, large temperature fluctuations (internal condensation), storage in the vicinity of aggressive agents must be avoided.

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