Brix (Soluble Solids)

Degrees Brix (°Brix) express the total soluble solids of a juice as a percentage by weight: a reading of 1 °Brix is what a solution of 1 g of sucrose in 100 g gives on the scale. In fruit juice the dissolved solids are mostly sugars, so the reading is used as a proxy for sweetness and ripeness. It is read on a refractometer, from a few drops of juice placed on the prism, and the EU marketing standards call the same figure the "refractometric index".

The reference method for a conformity check is the OECD Guidance on Objective Tests, which the EU marketing standards cite for the refractometric index and the sugar/acid ratio: a refractometer graduated in 0.1 °Brix, zeroed with distilled water, reading at 20 °C or corrected to it.

How an inspector samples Brix in a packhouse, following the OECD method:

• Number of fruits: at least 10 fruits of each size, taken at random from the reduced sample. For small fruit sold in punnets, such as strawberries, 10 sales packages and at least 5 fruits from each.
• Table grapes: at least 5 berries from each bunch or package, taken from different places on the bunch. The berries can be tested one by one or squeezed together; squeezing the whole bunch is also allowed.
• Citrus: each fruit is cut in half crosswise and squeezed to extract all the juice.
• Sound, dry fruit only: fruit with sun scorch, pest or disease damage is left out, because the damage may have altered ripening. The fruit must be dry, since external moisture mixing with the juice lowers the reading.
• Reading: an equal number of drops on the prism, result noted to one decimal place, prism rinsed with distilled water and wiped dry after every test.
• Decision: the individual readings are averaged. If the mean is equal to or above the limit in the standard, the lot meets the minimum maturity level. If 3 or more of the 10 readings are at least 10 per cent below the limit, a second sample is taken; if the average of the two samples is still at least 10 per cent below the limit, the lot fails, with no tolerance.

In a FoodGate Audit pre-shipment report, the Brix line therefore states the variety, the number of fruits or bunches sampled, each reading, the mean, the juice temperature and the standard or buyer specification the mean is compared against. For table grapes and citrus, sugar/acid balance and firmness are measured on-site alongside it.

What Brix does not say:

• Acidity: a refractometer cannot separate sugar from acid. The sugar/acid ratio needs a titration of the juice with an alkali (sodium hydroxide) according to the OECD method, and the ratio is what the EU citrus standard uses, not Brix alone. Two lots of oranges with the same Brix can taste very different if their acidity differs.
• Firmness: berry or fruit firmness is measured with a penetrometer, a separate objective test.
• Condition: Brix says nothing about decay, shatter, bruising, cold-chain breaks or pesticide residues. It is one line of the report, next to the defect counts sampled per AQL.

The EU marketing standard thresholds, verified in Commission Delegated Regulation (EU) 2023/2429, applicable since 1 January 2025 and replacing Implementing Regulation (EU) No 543/2011, which carried the same values for table grapes and oranges:

• Table grapes (Annex I, Part B, Part 9, section II.B, maturity requirements): the juice must have a refractometric index of at least 12 °Brix for Alphonse Lavallée, Cardinal and Victoria, 13 °Brix for all other seeded varieties and 14 °Brix for all seedless varieties. All varieties must in addition show satisfactory sugar/acidity ratio levels. Egyptian seedless exports such as Early Sweet, Flame Seedless, Superior and Crimson therefore sit at the 14 °Brix floor.
• Citrus fruit (Annex I, Part B, Part 2, section II.B): maturity is defined by minimum juice content, minimum sugar content, minimum sugar/acid ratio and colouring. The standard's table gives no minimum Brix figure for oranges or mandarins. The values are: satsumas 33 % juice and 6.5:1; clementines 40 % and 7.0:1; other mandarin varieties and hybrids 33 % and 7.5:1; blood oranges 30 % and 6.5:1; Navels group 33 % and 6.5:1; other orange varieties, which is where a Valencia falls, 35 % and 6.5:1; lemons 20 % juice with no ratio; grapefruit 35 % juice. Only Oroblanco (9 °Brix) and pummelos (8 °Brix) carry a Brix minimum. Juice content is determined by the OECD method on at least 2 kg of fruit, each fruit halved and pressed, juice weight divided by fruit weight.
• Strawberries (Annex I, Part B, Part 7, section II.A): the standard only requires the fruit to be "sufficiently developed and display satisfactory ripeness". There is no minimum Brix, no refractometric index and no sugar/acid ratio in the EU text. Any Brix floor on Egyptian strawberries comes from the buyer's specification, and that is the figure the inspector checks against.

Can a lot of grapes be rejected on Brix alone? Under the EU standard, yes: a refractometric index below the minimum for the variety means the lot does not meet the maturity requirements, and the OECD method applies no tolerance once the second sample confirms the shortfall. A buyer specification can set a higher floor, never a lower one.

Does a high Brix mean the fruit is good? No. It means the juice holds a high share of soluble solids. Eating quality also depends on acidity, firmness and condition, which is why the citrus standard works on ratio and juice content, and why FoodGate Audit reads Brix next to firmness and defect counts rather than as a stand-alone verdict.

Why does the inspector note the temperature of the juice? Because a refractometer that does not compensate for temperature is calibrated to read at a fixed temperature, usually 20 °C. Juice from a cold room or from fruit standing in the sun reads differently, and unless the instrument compensates automatically the reading has to be corrected with the ISO 2173 table. Recording the temperature makes the figure reproducible if the importer re-tests on arrival.

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