🍎 Total extract (dry soluble residue) in processed fruit and vegetable products — refractometry

Food chemistry Rozporządzenie (UE) 974/2014

Overview

The total extract (the content of soluble solids) is in juice-making practice the parameter number one: it decides the concentration, the conformity with the declaration, the settlement for the raw material, and whether a juice reconstituted from concentrated juice has the proper strength.

The reference document of this entry is a REGULATION, not a standard, and this is a deliberate choice. The whole course described below — the preparation of the sample, the temperature of the cell, the way of filtering, the dilution and the way of giving the result — comes from the annex to Commission Implementing Regulation (EU) No 974/2014 of 11 September 2014, which establishes the refractometric method for processed fruit and vegetable products for the purpose of their classification in the Combined Nomenclature. The same quantity is described by the standard PN-EN 12143:2000 (implementing EN 12143:1996, withdrawn by PKN on 24.04.2024 without a successor being indicated), but we did not have its text — from the catalogue card we know only the scope. If we had put the number of the standard in the heading and described below the course taken from the regulation, a reader working "according to PN-EN 12143" would get the procedure of a different document precisely where the standard has its own values unknown to us: the temperature corrections, the acidity correction for citrus juices and the repeatability limits. That is why the entry bears the number of the document from which it really comes.

The practical consequence for the laboratory: if your accreditation scope or your contract with the client cites PN-EN 12143, check the differences in the standard itself — both routes measure the same refractive index, but the details of the preparation of the sample and of the corrections may differ, and the test report states the document according to which the testing was done.

Status: the standard was withdrawn on 24.04.2024. The PKN catalogue card does not indicate a superseding standard, and the catalogue of the PKN shop contains no Polish implementation of the parallel standard ISO 2173 (Fruit and vegetable products — Determination of soluble solids — Refractometric method). A laboratory which has this test in its scope therefore has to decide on what document it will base its procedure — the measuring method itself remains in circulation regardless of the fate of the standard: an identical principle and course of action is kept in force by the customs law of the Union.

That second document, still in force, is Commission Implementing Regulation (EU) No 974/2014, establishing the refractometric method for measuring the dry soluble residue (the Brix value) in processed fruit and vegetable products for the purpose of their classification in the Combined Nomenclature. It came into being because, despite the removal of Regulation (EEC) No 558/93 from the body of law, the refractometric method is still used in the customs laboratories of the Member States as an important and irreplaceable tool serving to determine the content of sugars expressed as sucrose. The course of the determination and the requirements for the refractometer given below come from the annex to that regulation — it is a document separate from PN-EN 12143 and describes its own customs method, not the content of the standard; when working on the standard one has to keep to its text.

In research practice the result is given in degrees Brix. Polish scientific papers of recent years determine the refractometric extract of juices expressly „zgodnie z normą PN-EN 12143:2000" [in accordance with the standard PN-EN 12143:2000] and express it in °Bx — this was done in examining mixed juices of chokeberry and honeysuckle berry (refractometer Refracto 30PX, Mettler Toledo) and in assessing the quality of citrus fruit (determination of the total extract by the refractometric method in accordance with that standard).

What this description does not contain: we have not seen the text of the standard — PKN supplies it for a fee, and after its withdrawal only in archival form. The values of the temperature corrections for juices, the way of carrying out the acidity correction for citrus juices and the numerical limits of repeatability and reproducibility from interlaboratory trials are in the standard, but we do not quote them — they have to be read from its text. A table of temperature corrections is also given by the annex to Regulation (EU) No 974/2014, but it is a table from that document and must not be equated with the table of the standard.

WHAT THIS METHOD DOES NOT CONTAIN AND THE PARALLEL STANDARD DOES: if you are testing according to PN-EN 12143, the standard additionally provides a so-called acidity correction for juices of citrus fruit — Regulation (EU) No 974/2014 does not provide for it at all and it is not in the procedure described below. The way of carrying out that correction is unknown to us: it is given by the text of the standard, which we did not have. The standard also contains data on repeatability and reproducibility from interlaboratory trials, which the regulation does not give.

THE NUMBER OF THE LEGAL ACT DOES NOT STAND AT THE BEGINNING OF THE STRING — THE ZERO IN THE TAB IS FALSE, AND IT CANNOT BE FIXED WITH THE KEY (23.09.2026). The key of the "Laboratories" tab has the form "Rozporządzenie (UE) 974/2014" and gives 0 entries at 0 laboratories. The measurement showed, however, that THIS REGULATION IS IN THE SCOPES — at THREE laboratories, in three different forms, and in none of them does the number stand at the beginning of the value (23.09, copy of the scopes, search for the string "974" in the whole set): • AB 411 — "Rozporządzenie wykonawcze Komisji (UE) nr 974/2014 z dnia 11 września 2014 r., Załącznik (Dz.U. L 274 z 16.9.2014)"; • AB 826 — "Rozporządzenie wykonawcze Komisji (UE) Nr 974/2014 z dnia 11 września 2014 r., załącznik" (difference: "Nr" with a capital letter); • AB 592 — "Rozporządzenie Komisji (WE) nr 974/2014 z dnia 11 września 2014 r. załącznik (Dz.U. L 274 z 16.9.2014 z późn. zm.)" — with an ERROR in the scope itself: the act is a (UE) [EU] regulation, not a (WE) [EC] one. Matching in the tab works by the BEGINNING of the value, and the beginning here is not the number but the generic name of the act. No prefix will cover the three records above without also pulling in others: "Rozporządzenie wykonawcze Komisji (UE)" [Commission Implementing Regulation (EU)] gives 37 entries at 12 laboratories (dozens of other regulations), "Rozporządzenie Komisji (WE)" [Commission Regulation (EC)] — 76 at 19, and "Rozporządzenie" [Regulation] alone — 800 entries at 95 laboratories in 689 different forms of the record. THAT IS WHY THE KEY STAYS AT THE EXACT FORM: a list of three laboratories that the tab will not show is less harmful than a list of a dozen or more that do not perform this method — and the reader has these three numbers above. THE SCALE OF THIS CLASS IN THE WHOLE SET: 898 ENTRIES AT 100 LABORATORIES have as their reference document a legal act with the number in the middle of the value. For standards the designation of the document is a prefix and the matching mechanism works; FOR LEGAL ACTS IT NEVER IS, so this whole domain is inaccessible to matching by the beginning by design, not through a mistake in any particular entry. CORRECTION OF THE FIGURE ORIGINALLY GIVEN HERE (23.09.2026). Until now this place read "1072 entries", with the breakdown: 800 "Rozporządzenie", 120 "Regulation", 71 "Dyrektywa" [Directive], 46 "Ustawa" [Act], 21 "Directive", 14 "Obwieszczenie" [Announcement]. EACH OF THESE SIX COMPONENTS IS TRUE, BUT THEIR SUM IS NOT THE NUMBER OF ENTRIES — THE CATEGORIES ARE NOT DISJOINT. One entry may cite several acts at once and is then counted in several components: the measurement of the distribution (23.09) gives 696 entries with one act, 126 with two, 31 with three, 21 with four, and beyond that a few each with five, six, seven, eight and ten. THE EXCESS OF THE SUM AMOUNTS TO 174 ENTRIES counted more than once. THE CORRECT STATEMENT OF THIS SCALE IS THEREFORE: 898 entries at 100 laboratories in the set, and 1072 — the sum of the hits of six separate patterns. Both numbers are true and answer two different questions; the one that was given was the one nobody had asked about.

Method principle

The principle is to infer the content of soluble solids from the refractive index of the product. The content of dry soluble residue (the Brix value determined refractometrically) is the mass percentage of sucrose in an aqueous sucrose solution which under defined conditions has the same refractive index as the product analysed. In other words: the refractometer does not measure sugar but refraction, and expresses the result on a conventional sucrose scale — which is why with products containing other dissolved substances the result is an approximation, conventionally taken as the content of soluble solids. The reading is made on the sugar scale of the refractometer in mass percentages of sucrose, and the result is referred to the reference temperature of 20 °C; a measurement made at another temperature requires a correction. The standard PN-EN 12143 additionally provides for juices of citrus fruit a so-called acidity correction; the way of carrying it out is given by the text of the standard.

Applications

• Control of the extract of fruit and vegetable juices and of concentrated juices — the basic parameter on acceptance and in settling for the raw material
• Checking the strength of a juice reconstituted from concentrated juice (conformity with the degree Brix declared for the given kind of fruit)
• Assessment of the ripeness and quality of fruit raw material before processing
• Scientific studies of the quality of juices — the refractometric extract in °Bx as a characteristic controlled before and after storage
• Customs classification of processed fruit and vegetable products in the Combined Nomenclature — on the basis of the refractometric method of Regulation (EU) No 974/2014
• Control of the process of concentration and standardisation in a processing plant

Key parameters

Standard

Standard number

Rozporządzenie wykonawcze (UE) nr 974/2014

Title (PL)

Rozporządzenie wykonawcze Komisji (UE) nr 974/2014 określające metodę refraktometrii polegającą na pomiarze suchych rozpuszczalnych pozostałości w przetworach owocowych i warzywnych do celów ich klasyfikacji w Nomenklaturze scalonej

Title (EN)

Commission Implementing Regulation (EU) No 974/2014 establishing the refractometric method for the measurement of dry soluble residue in fruit and vegetable processed products for the purpose of their classification in the Combined Nomenclature

Step-by-step procedure

1. Checking and calibrating the refractometer

   The instrument must permit a reading of the mass percentage of sucrose to an accuracy of ±0.1 % and be calibrated at 20 °C, with the possibility of setting the cell temperature in the range from +15 °C to +25 °C to an accuracy of ±0.5 °C. Follow the operating instructions strictly, especially the part on calibration and the light source.

2. Preparing the sample — liquid products

   Mix the clear juice carefully and proceed to the determination.

3. Preparing the sample — juices with suspended matter, purées

   Mix the average laboratory sample carefully and homogenise it. Strain part of the sample through dry gauze folded in four, discard the first drops and carry out the determination on the filtrate.

4. Preparing the sample — thick products

   If the product cannot be used directly: weigh out 40 g to an accuracy of 0.01 g into a 250 ml beaker, add 100 ml of distilled water, heat carefully for 2–3 minutes while stirring with a rod, cool, transfer quantitatively into a tared vessel, make up with water to about 200 g, weigh to an accuracy of 0.01 g and mix. Leave to stand for 20 minutes, filter through a fluted filter or a Büchner funnel and carry out the determination on the filtrate.

   ⏱ Time: 20 min

5. Bringing to the measuring temperature

   The measuring temperature is to lie between 15 and 25 °C; with a digital refractometer — 20 °C. Bring the sample to that temperature by immersing the container in a water bath.

   🌡 Temperature: 15–25 °C (digital: 20 °C)

6. Placing the sample on the prism

   Place a small quantity of the sample on the lower prism, making sure that it covers the glass surface evenly at the moment when the two prisms are pressed together.

7. Reading

   Carry out the measurement in accordance with the operating instructions of the instrument. Read the mass percentage of sucrose to an accuracy of 0.1 %. Make at least two determinations from the same prepared sample.

8. Temperature correction

   If the reading was made at a temperature other than 20 °C, correct it according to the table of corrections (the standard gives its own values of the corrections for substances determined refractometrically; Regulation (EU) No 974/2014 has its own Table 1 — do not mix the two sources).

9. Conversion in the case of dilution and the result

   If the measurement was made on a diluted solution, convert the result to the original product on the basis of the mass of the product in the solution. Express the content of soluble solids in grams per 100 g of product, which corresponds to the Brix value, and give it to one decimal place (±0.1 °Brix).

10. Test report

    Give the result in °Bx together with the measuring temperature, information on any acidity correction and on the dilution of the sample, and the reference document cited — when citing PN-EN 12143:2000, note that the standard is withdrawn.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The method requires no chemical reagents — the main hazards are mechanical and thermal.
• The prism of the refractometer is of glass and is easily scratched — clean it only with a soft cloth, do not scrape off sugar deposits.
• When preparing thick and dry products one works with a boiling water bath and hot beakers — use heat-resistant gloves and holders.
• Juice samples with added alcohol are heated in a water bath — keep them away from naked flames, work with ventilation.
• Fruit juices are a medium for microorganisms and moulds — remove the remains of samples as you go, wash the working place after work.

Frequently asked questions