The principle is the deduction of the dry soluble residue content of a product from its refractive index.

The measurement temperature shall be between 15 and 25 °C.

By using a digital refractometer the temperature shall be at 20 °C.

Bring the sample to the measurement temperature by immersing the container in a water bath at the required temperature.

Place a small sample on the lower prism of the refractometer, taking care to ensure that the sample covers the glass surface uniformly when the prisms are pressed against each other.

Measure in accordance with the operating instructions for the apparatus used.

Read the percentage weight of sucrose to the nearest 0,1 %.

Make at least two determinations on the same prepared sample.

The dry soluble residue content is expressed in grams per 100 grams of the product (g/100 g). This is equivalent to a value in °Brix.

The dry soluble residue content shall be calculated as follows:

The percentage sucrose content indicated by refractometry shall be used directly.

If the reading is made at a temperature other than + 20 °C, correct as indicated in table 1.

If the measurement has been made on a diluted solution, the dry soluble residue content (M) shall be calculated using the following formula:

M' being the weight (in grams) of dry soluble residue per 100 g of product indicated by the refractometer and E the weight (in grams) of product per 100 g of solution.

The result of that calculation shall be given to one decimal place (+/- 0,1 °Brix).

Corrections when determination is made at a temperature other than 20 °C

Temperature °C	Sucrose in grams per 100 grams of product
	5	10	15	20	30	40	50	60	70	75
	Subtract
15	0,25	0,27	0,31	0,31	0,34	0,35	0,36	0,37	0,36	0,36
16	0,21	0,23	0,27	0,27	0,29	0,31	0,31	0,32	0,31	0,23
17	0,16	0,18	0,20	0,20	0,22	0,23	0,23	0,23	0,20	0,17
18	0,11	0,12	0,14	0,15	0,16	0,16	0,15	0,12	0,12	0,09
19	0,06	0,07	0,08	0,08	0,08	0,09	0,09	0,08	0,07	0,05
	Add
21	0,06	0,07	0,07	0,07	0,07	0,07	0,07	0,07	0,07	0,07
22	0,12	0,14	0,14	0,14	0,14	0,14	0,14	0,14	0,14	0,14
23	0,18	0,20	0,20	0,21	0,21	0,21	0,21	0,22	0,22	0,22
24	0,24	0,26	0,26	0,27	0,28	0,28	0,28	0,28	0,29	0,29
25	0,30	0,32	0,32	0,34	0,36	0,36	0,36	0,36	0,36	0,37

The precision data were determined from an inter-laboratory test that was carried out in 1999/2000 with the participation of the European Customs Laboratories.

The evaluation of the precision data was performed according to ISO 5725.

Precision data

Sample name	Number of laboratories	Mean (°Brix)	Repeatability limit r (%)	Reproducibility limit R (%)
Fruit cocktail	11	18,9	3,0	4,7
Pineapple	10	19,4	1,7	1,7
Apple compote	12	19,5	2,0	2,7
Tropical fruit	9	12,8	2,9	4,0
Strawberry jam	12	59,8	4,0	7,2
Apple juice	12	11,1	1,4	4,7
Orange juice concentrate	9	65,2	1,3	2,6
Powder orange juice	11	99,8	2,3	5,3