🍎 Determination of fat content by the Weibull-Berntrop gravimetric method (reference method) in milk and liquid, concentrated or dried milk products for which the Röse-Gottlieb method does not work (high free fatty acids, lumps, non-milk ingredients insoluble in ammonia — e.g. flans, oat porridges, some dairy products for bakeries), and in fresh cheese, also with fruit, syrup or muesli — the test portion is boiled with hydrochloric acid of about 20 %, the hot solution is filtered through a moistened filter paper retaining the fat, the filter is dried, the fat is extracted with n-hexane or light petroleum 30–60 °C in a Soxhlet-type apparatus, the solvent is evaporated and the residue weighed; result in percent by mass, with blank tests of the solvent (≤ 1,0 mg) and filters (≤ 2,5 mg), PN-ISO 8262-3

Food chemistry PN-ISO 8262-3

Overview

WHAT THE STANDARD COVERS. We read the text of the standard in the iTeh sample of ISO 8262-3:2005 | FIL 124-3:2005 in the French version (“Produits laitiers et produits à base de lait — Détermination de la teneur en matière grasse par la méthode gravimétrique Weibull-Berntrop (Méthode de référence) — Partie 3: Cas particuliers”, second edition of 01.11.2005): title page, contents, ISO and IDF forewords, introduction and Clauses 1–6 — the sample ends on page 3, before Clause 7 (procedure). We do not read the procedure (sample preparation, test portion, blank test, flask preparation, determination), calculation, precision, notes on procedure and the test report (Clauses 7–11); we know the titles from the contents.

ACCORDING TO THE TEXT OF ISO 8262-3:2005. The standard was prepared by ISO/TC 34 “Food products”, Subcommittee SC 5 “Milk and milk products”, together with the International Dairy Federation (IDF), under the joint ISO-IDF action team on fat determination (E 31); this edition cancels and replaces ISO 8262-3:1987 and IDF 126A:1988 as a minor revision. The series ISO 8262 | IDF 124: Part 1 — infant foods, Part 2 — edible ices and ice mixes based on milk, Part 3 — special cases. Introduction: the series belongs to a set of harmonized reference methods for determining fat in milk, milk products and milk-based foods — by the Röse-Gottlieb (RG), Weibull-Berntrop (WB) or Schmid-Bondzynski-Ratzlaff (SBR) principle; WB was chosen for milk and liquid, concentrated or dried milk products made under poor conditions and/or with insoluble non-milk ingredients because: a) with much free fatty acid or with lumps and non-milk ingredients insoluble in ammonia, extraction in RG is incomplete; b) a high carbohydrate content increases in SBR the amount of ether-extractable compounds after acid hydrolysis and raises the result; c) in WB the hydrolysate is filtered and washed, and the dried residue on the filter contains no compounds extractable by light petroleum; d) the method is used for this purpose in many countries; Weibull’s original method was applied to bread, and Berntrop developed a heavily modified version. Scope (1): reference method for the fat content of milk and liquid, concentrated or dried milk products for which the Röse-Gottlieb method is unsuitable because they contain significant amounts of free fatty acids or do not dissolve completely in ammonia owing to lumps or non-milk ingredients — e.g. flans, oat porridges, some dairy products for the bakery trade; Note 1 — RG methods for milk, cream, sweetened condensed milk and dried products are in ISO 1211, ISO 2450, ISO 1737 and ISO 1736; the method also applies to fresh cheese (quark, fresh cheese) and fresh cheese with fruit, syrup, muesli etc., for which SBR is unsuitable because of a higher carbohydrate content and/or extreme heterogeneity; Note 2 — SBR for cheese and processed cheese with a lactose content below 5 % (mass fraction) of the fat-free dry matter is described in ISO 1735. Definition (2.1): fat content — all substances determined by this method, in percent by mass. Principle (3): hydrolysis of the test portion by boiling with dilute hydrochloric acid, filtration of the hot hydrolysate through a wet filter paper retaining the fat, extraction of the fat from the dried filter with n-hexane or light petroleum, removal of the solvent by distillation or evaporation and weighing. Reagents (4): analytical grade, without significant residue; distilled or demineralized water; hydrochloric acid of about 20 % (100 ml concentrated HCl of density 1,18 g/ml + 100 ml water, density about 1,10 g/ml); anhydrous solvent — n-hexane or light petroleum boiling at 30–60 °C, checked by distilling 100 ml from a prepared flask (residue not more than 1,0 mg, otherwise replacement or distillation); fluted filter papers 150 mm, medium speed, preferably defatted, checked by a blank test (residue not more than 2,5 mg); indicator paper; diatomaceous earth and pure lactose (optional, 7.5.3); cotton wool defatted by solvent extraction for 1,5 h. Apparatus (5): warning — with volatile flammable solvents, electrical equipment must comply with the regulations for such hazards; analytical balance; mill (e.g. high-speed with a 1 l bowl with lid); continuous or semi-continuous extraction apparatus, e.g. Soxhlet type — 150 ml flat-bottomed narrow-neck flask, extractor siphoning 40–60 ml, reflux condenser with a drying tube or cotton wool; thimbles of defatted paper, glass, aluminium oxide, PTFE or single-layer cellulose, 22 mm × 80 mm, without residue in the blank; water baths 40–60 °C and 30–40 °C; fat-free boiling aids; 250 ml conical flask with reflux condenser (preferably Liebig); apparatus for distilling the solvent below 100 °C; drying oven with open vents, 102 ± 2 °C uniformly throughout the chamber, with thermometer. Sampling (6): not part of the method, recommended procedure in ISO 707 | IDF 50; liquid, viscous and pasty samples are kept at 2–4 °C from sampling to analysis, and closed cans or bottles — unopened, below 20 °C.

STATUS (as of 03.10.2026). In the PKN search (term “8262-3”, 03.10.2026) PN-ISO 8262-3:2011 (Polish version, “Introduces: ISO 8262-3:2005 [IDT]”) has no withdrawal note; PN-ISO 8262-3:2002 — “Withdrawn and replaced by” PN-ISO 8262-3:2011. Card of PN-ISO 8262-3:2011: publication date 19.07.2011, 14 pages, KT 35 Milk and Milk Products, ICS 67.100.01, “Replaces PN-ISO 8262-3:2002”, no withdrawal note. In the iTeh catalogue (read 03.10.2026) ISO 8262-3:2005 has the status “Published”, stage 90.92 (international standard to be revised), since 24.04.2025.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, load up to 17.09.2026, read 03.10.2026). The number 8262-3 appears in 3 records at 3 laboratories: AB 285, AB 452, AB 1334. In the current PCA documents (read 03.10.2026; AB 452 issue No. 25 of 30.10.2025, AB 285 issue No. 28 of 13.01.2026, AB 1334 issue No. 31 of 04.05.2026) the number appears in 3 lines at the same 3 laboratories; in each document the number of page markers equals the number of PDF pages, without repetitions; a search of all PCA documents downloaded from the BIP on 03.10.2026 found no laboratories outside the database copy. The form is always “PN-ISO 8262-3:2011”, at AB 285 in one cell with PN-ISO 13580:2017-03 and “PN-EN 7208:2010” (as written in the document). None of these items is suspended. The “Laboratories” tab (term “PN-ISO 8262-3”) shows all 3 laboratories — checked by a tab query on the labcoda.pl production server on 03.10.2026.

WHAT THE LABORATORIES TEST (items in PCA). AB 452: milk products and milk-based products — total fat content (1,0–42,0) %, gravimetric method (Soxhlet extraction); AB 1334: milk and milk products — fat content after hydrolysis (0,10–99,00) %, gravimetric method; AB 285: fermented milk drinks — fat-free dry matter content by calculation, with three documents in one cell.

WHERE AN APPARENTLY CORRECT RESULT IS EASY TO GET. With the choice of method: this is a method for special cases — milk and liquid concentrated or dried products where RG fails, and fresh cheese where SBR fails (1); for ordinary milk, cream, condensed milk and powders the reference methods are ISO 1211, ISO 2450, ISO 1737 and ISO 1736 (Note 1), and the items of AB 452 and AB 1334 describe the object in general terms (“milk products”, “milk and milk products”). With residues: solvent up to 1,0 mg and filters up to 2,5 mg in the blank (4.2, 4.3) — at low fat contents (AB 1334 from 0,10 %) this is a significant part of the result. With the sample: storage at 2–4 °C, cans and bottles unopened below 20 °C (6). With the quantity: AB 285 gives fat-free dry matter by calculation — PN-ISO 8262-3 gives only fat, and the dry matter comes from another document in the same cell.

WHAT WE DO NOT GIVE. We do not quote sample preparation, test portions, the course of hydrolysis and extraction, the formula, precision data or the test report (Clauses 7–11) — they lie outside the sample. We have not read PN-ISO 13580 or the RG and SBR standards.

Method principle

The test portion is boiled with hydrochloric acid of about 20 %, which releases fat from proteins and carbohydrates; the hot hydrolysate is filtered through a moistened filter paper that retains the fat, while water-soluble compounds pass into the filtrate. The dried filter is extracted with n-hexane or light petroleum in a Soxhlet-type apparatus, the solvent is distilled off or evaporated and the residue weighed; the fat content is the mass of the extract in percent of the mass of the test portion, corrected for the blanks.

Applications

• Fat in milk and liquid, concentrated or dried milk products with free fatty acids, lumps or non-milk ingredients (flans, oat porridges, products for the bakery trade) (1)
• Fresh cheese, also with fruit, syrup or muesli (1)
• Milk products, milk, fermented milk drinks — items in the accreditation scopes of 3 laboratories in PCA

Key parameters

Standard

Standard number

PN-ISO 8262-3:2011

Title (PL)

Przetwory mleczne i żywność na bazie mleka — Oznaczanie zawartości tłuszczu metodą grawimetryczną Weibulla-Berntropa (Metoda odniesienia) — Część 3: Przypadki szczególne

Title (EN)

Milk products and milk-based foods — Determination of fat content by the Weibull-Berntrop gravimetric method (Reference method) — Part 3: Special cases

Step-by-step procedure

1. Sample

   Storage at 2–4 °C (cans and bottles unopened below 20 °C), grinding if necessary (5.2, 6). PN-ISO 8262-3:2011 without a withdrawal note in PKN (03.10.2026).

2. Checking reagents

   Blank test of the solvent (≤ 1,0 mg) and filters (≤ 2,5 mg) (4.2, 4.3).

3. Hydrolysis and filtration

   Boiling the test portion with HCl under reflux, hot filtration through a wet filter, washing and drying (3; details in 7, outside the sample).

4. Extraction

   Filter in a thimble, extraction with n-hexane or light petroleum in a Soxhlet apparatus (3, 5.3).

5. Result

   Distilling off the solvent, drying at 102 ± 2 °C, weighing; fat in % by mass (2.1, 3; formula in 8, outside the sample).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Volatile, flammable solvents — electrical equipment complying with the regulations for such hazards (warning in 5)
• Boiling hydrochloric acid — work in a fume hood, eye and hand protection

Frequently asked questions