🍎 Maize — moisture content of grains, ground grains, groats, grits and maize flour by the gravimetric method: reference method (drying 4 h at 130–133 °C, pre-conditioning of moist grain) and routine method on whole grains; PN-EN ISO 6540

Food chemistry PN-EN ISO 6540

Overview

WHAT THE STANDARD COVERS. ISO 6540:2021 (clause 1) specifies two methods: a reference method for the determination of the moisture content of maize grains and ground whole maize, groats, grits and maize flour (clause 4) and a routine method for the evaluation of the moisture content of maize in whole grains (clause 5). The routine method is not suitable for experts’ reports or for the calibration and checking of humidity meters because of its significant bias to the reference method (Table B.3). Moisture content of maize (point 3.1) — loss in mass undergone by a product under specified conditions, expressed as a percentage. The standard has no normative references. Introduction: the methods for cereals in ISO 712 apply only to cereals other than maize and to cereal products; the basic reference method for maize — the “absolute method” (Annex A) — requires special equipment and experienced personnel and can only be applied in specialized laboratories; maize can be very moist (sometimes above 40 %, mass fraction), and the size and texture of the grains make grinding and pre-drying difficult — hence the whole-grain method: easier, allowing work in series, with a longer response time and a lower workload, but with a positive bias of about 0.30 % (mass fraction) compared with the reference method. The standard was prepared by Technical Committee ISO/TC 34 “Food products”, Subcommittee SC 4 “Cereals and pulses”, in collaboration with CEN/TC 338 “Cereal and cereal products” (Vienna Agreement). The second edition replaced ISO 6540:1980 after technical revision: former clauses 7–10 and 17–20 (now 4.5–4.9 and 5.4–5.7) and the annexes were revised.

REFERENCE METHOD — PREPARATION OF THE SAMPLE (points 4.1–4.4, 4.8). Principle: if necessary, grinding of the sample, after pre-conditioning if required, and drying of the test portion at 130–133 °C under conditions that give a result in agreement with that of the absolute method. Sampling is not part of the method; recommended method — ISO 24333; the laboratory should receive a truly representative sample, in a sealed package, undamaged and unmodified during transport and storage. A product with particles ≤ 1.7 mm, in which less than 10 % (mass fraction) of the particles is over 1 mm and more than 50 % below 0.5 mm, does not need grinding. Grinding without pre-conditioning — for products whose moisture content does not change during grinding (generally from 9.00 % to 15.00 %): quickly about 30 g, mix with a spatula and determine immediately. With pre-conditioning — when the moisture content exceeds 15.00 % (the more frequent case) or is below 9.00 %: about 100 g, weighed to the nearest 0.1 g in a metal boat, is kept in an oven at 60–80 °C until a moisture content of 9.00–15.00 % is reached, then left in the laboratory atmosphere (at least 2 h) until the sample returns to laboratory temperature and the moisture is distributed fairly uniformly — without adding or removing material, at most under a sheet of paper, not under a lid, which would limit the exchange of moisture; after conditioning the sample is weighed to the nearest 0.1 g and about 30 g is ground quickly. A product with a moisture content below 9.00 % is left in a suitable atmosphere (usually that of the laboratory) until the moisture content is within that range. Notes on procedure (4.8): the range in which conditioning is not needed corresponds to a laboratory at (20 ± 2) °C and 45–75 % relative humidity, and should be modified for other conditions; conditioning 100 g and grinding 30 g for an 8 g test portion are intended to give a more representative sample — grinding only 8 g would lead to too great a dispersion of the results.

REFERENCE METHOD — DETERMINATION (points 4.2, 4.5). Two determinations on two ground test portions; if the absolute difference between the results exceeds the repeatability limit, the determination is repeated. About (8 ± 1) g is weighed quickly to the nearest 0.001 g into each of two metal capsules tared to the nearest 0.001 g; the capsule is non-corrodible under the test conditions (or a glass dish), has a tight-fitting lid and a surface area allowing the test portion to be spread at no more than 0.3 g per cm². The open capsule with its lid is dried in an oven at 130–133 °C for 4 h ± 5 min. Moist products must not be placed in an oven with test portions at the end of drying, the door must not be opened during drying, and new wet samples must not be introduced before the dry ones are removed — the dry portions would then take up moisture again. After drying, cover quickly, transfer to the desiccator (without placing dishes on top of one another) and, after cooling to laboratory temperature (generally after 30–45 min), weigh to the nearest 0.001 g. Apparatus: analytical balance with an accuracy of ±0.001 g (display 0.000 1 g) and a balance with an accuracy of ±0.1 g (display 0.01 g); grinding mill of material that does not absorb moisture, easy to clean, with as little dead space as possible, grinding 30 g of grain rapidly and uniformly, without appreciable heating and, as far as possible, without contact with the outside air, adjustable to the particle sizes of 4.4.1; metal boat without lid on which 100 g of grain lies in a single layer; electrically heated oven adjustable between 60 °C and 80 °C, with ventilation; electrically heated oven keeping 130–133 °C near the test portions which, set to 131 °C and loaded with the maximum number of test portions, returns to this temperature in less than 45 min (preferably less than 30 min); the effectiveness of the ventilation is checked with durum wheat semolina with particles up to 1 mm — with full loading, the results after 2 h and after a further 1 h of drying must not differ by more than 0.15 g of moisture per 100 g of sample; desiccator with an efficient desiccant.

RESULT AND PRECISION (points 4.6–4.7, 4.9). Moisture content wH2O as a percentage by mass of the product as received. Without pre-conditioning: wH2O = (m0 − m1) × 100 / m0, where m0 = m′0 − t — mass of the test portion, m1 = m′1 − t — mass of the test portion after drying, t — tare of the capsule. With pre-conditioning: wH2O = [(m0 − m1) × m3 / m0 + m2 − m3] × 100 / m2 = 100 × (1 − m1·m3 / (m0·m2)), where m2 — mass of the sample before conditioning, m3 — after conditioning. The result is the mean of the two values, provided that the repeatability requirement is met, given to two decimal places. The precision data from the interlaboratory test (Annex B) apply only to moisture contents from 11.90 % to 39.20 % and only to maize: repeatability limit r = 2.8 × sr = 2.8 × 0.07 = 0.19 (point 4.7.2); critical difference of two means (each of two results) within one laboratory Dr = 1.98 × sr = 0.14 (Formula 3), and between two laboratories DR = 0.68 (Formula 4) — the results of two laboratories are compared using the critical difference. The expanded uncertainty should be no more than ±2 reproducibility standard deviations (point 4.7.6). Compared with the absolute method, the results generally differ by less than 0.15 g of water per 100 g of sample (point 4.7.7). Test report (4.9): information identifying the sample, reference to ISO 6540, date and type of sampling procedure (if known), date of receipt and date of the test, results with units, operations not specified in the standard or optional which might have affected the result.

ROUTINE METHOD ON WHOLE GRAINS (clause 5 — titles only in the fragment we read). Table of contents: principle, apparatus, sampling, test portion, drying, number of determinations, method of calculation, repeatability, reproducibility, comparison of two groups of measurements within one and between two laboratories, application of fidelity limits (Annex C), remark, test report. The PKN card of the withdrawn PN-ISO 6540:1994 (ISO 6540:1980) describes the routine method as drying whole grains for 38 h at a temperature from 130 °C to 133 °C; whether the 2021 edition kept this time is not in the fragment we read.

STATUS (PKN card as of 07.11.2026). The card of PN-EN ISO 6540:2021-08 (English version) has no withdrawal note: published 27-08-2021, 38 pages, Food, Agriculture and Forestry Sector, KT 36 Cereals and Cereal Products, “Adopts: EN ISO 6540:2021 [IDT], ISO 6540:2021 [IDT]”, “Replaces: PN-EN ISO 6540:2010 - English version, PN-EN ISO 6540:2010 - Polish version”, ICS 67.060; Polish title “Kukurydza -- Oznaczanie wilgotności (rozdrobnionego i całego ziarna)”. There is no card of a Polish version of the 2021 edition in the PKN shop. Earlier editions (PKN cards, 07.11.2026): PN-ISO 6540:1994 (adopted ISO 6540:1980 [IDT], replaced PN-A-74011:1986) — withdrawn 29-06-2010, replaced by PN-EN ISO 6540:2010; PN-EN ISO 6540:2010 — Polish version published 15-10-2015, adopted EN ISO 6540:2010 and ISO 6540:1980 [IDT], withdrawn 27-08-2021 and replaced by PN-EN ISO 6540:2021-08 (the English version of the 2010 edition — also “withdrawn and replaced by” PN-EN ISO 6540:2021-08). The 1994 and 2010 editions thus carried the same text of ISO 6540:1980; the change of content came with ISO 6540:2021. ISO page (read on 07.11.2026): ISO 6540:2021 — “Published”, edition 2, published 2021-02-19, 25 pages, ISO/TC 34/SC 4, ICS 67.060; systematic review started 2026-01-15 and closed 2026-06-05 (stage 90.60) — the page does not give a decision on confirmation or revision. Other standards named in the entry (PKN cards, 07.11.2026): PN-EN ISO 712:2012 — withdrawn 03-03-2025, replaced by PN-EN ISO 712-1:2025-03 (card without a withdrawal note; adopts ISO 712-1:2024); a standard “PN-ISO 712:2012” from the scope of AB 583 does not exist in the PKN shop — there is PN-EN ISO 712:2012; PN-A-74108:1996 “Pieczywo -- Metody badań” (bread — test methods) — withdrawn 31-10-2023; PN-EN ISO 24333:2012 “Ziarno zbóż i przetwory zbożowe -- Pobieranie próbek” (cereals and cereal products — sampling) (Polish version, adopts ISO 24333:2009) — card without a withdrawal note.

REGULATION. Commission Implementing Regulation (EU) 2016/1240 (public intervention and aid for private storage), Annex I Part II point b: standard method for determining the moisture content for maize: standard EN ISO 6540, and for cereals other than maize — EN ISO 712 or an infrared method according to EN 15948; in case of dispute only the results of applying EN ISO 6540 for maize and EN ISO 712 for cereals other than maize are binding (our translation of the Polish text). Article 4(2) (as worded by Commission Implementing Regulation (EU) 2018/150): the methods are those of the latest versions of the relevant European or international standards in force at least 6 months before the first day of the public intervention period. The consolidated text of 07.02.2018 is the latest in the EUR-Lex list (read on 07.11.2026). This provision concerns cereals in public intervention, not every test of maize.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, read on 07.11.2026; “Laboratories” tab on labcoda.pl, 07.11.2026). The number 6540 in the reference document field appears in 7 items at 6 Polish laboratories: AB 103 (2 items), AB 411, AB 583, AB 1179, AB 1275, AB 1616 (1 each). Forms: “PN-EN ISO 6540:2021-08” — 5 items (two at AB 103, AB 1275, AB 1616, and at AB 411 together with the procedure “PU-10 V-2 wydanie z dnia 15.07.2022 r.”), “PN-EN ISO 6540” without a date (AB 1179) and “PN-ISO 6540:1994” — the edition withdrawn in 2010 (AB 583, in one item with the entries “PN-ISO 712:2012” and “PN-A-74108:1996 pkt 3.3.2”). Outside Poland there are 3 items at 3 Czech laboratories (1463, 1481, 1727), in which “ČSN EN ISO 6540” or “ČSN ISO 6540” appears in brackets of an in-house procedure (SOP) next to other moisture standards. The “Laboratories” tab (“PN-EN ISO 6540”, matching by the beginning of the entry — it also catches the entries “PN-ISO 6540” and “ČSN …”) shows 9 laboratories: 6 Polish and 3 Czech, AB 103 with two items, the others with one — the same as the copy. We did not compare the current PCA scope documents of these laboratories with the copy.

WHAT THE LABORATORIES TEST (database copy, complete items). Maize, moisture or water content, gravimetric method: AB 103 — “Agricultural products: Maize”, (12.58–37.84) %, and “Maize”, (13.0–35.0) %; AB 1616 — maize, (9.00–40.00) %; AB 411 — maize grain, (9.00–25.00) % by mass; AB 1275 — maize grains, (7.0–35.0) %; AB 1179 — maize (entry “KukurydzaE)” with a footnote marker whose content we did not check), water content, no range given. AB 583 — cereals and cereal products, water content (2.5–43) % and dry matter (calculated), in one item with three documents. No item states whether the laboratory uses the reference method (clause 4) or the routine method (clause 5) — all of them write only “gravimetric method”. Czech: 1463 — cereals and their products, oilseeds, pulses, feed; 1481 — food, feed and agricultural products; 1727 — oilseeds, plant material, cereal mixtures (sum of moisture and volatile matter).

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. Preparation: maize with a moisture content above 15.00 % or below 9.00 % changes its moisture during grinding and must first be pre-conditioned (point 4.4.2.3); grinding only 8 g instead of 30 g gives too great a dispersion (point 4.8.2); the 9–15 % range applies to a laboratory at (20 ± 2) °C and 45–75 % relative humidity (point 4.8.1). Choice of method: the routine method on whole grains has a positive bias of about 0.30 % and is not suitable for experts’ reports or for the calibration and checking of moisture meters — yet the scopes write only “gravimetric method” for all items; a result that does not state the clause of the standard does not say whether it is a reference result. Measurement: the oven must return to 131 °C after full loading in less than 45 min and pass the ventilation check; placing wet samples in an oven with test portions at the end of drying rehydrates them — mass m1 increases and the moisture result decreases. Calculation: after pre-conditioning the result is calculated with Formula (2) using masses m2 and m3 — Formula (1) applied to the conditioned sample gives the moisture of the pre-dried sample (9–15 %), not of the maize as received, because it omits the water lost during conditioning (m2 − m3); both masses are measured in this method (balance ±0.1 g). The precision data (r = 0.19; Dr = 0.14; DR = 0.68) apply only from 11.90 % to 39.20 %; the scopes of AB 1616 (from 9.00 % to 40.00 %), AB 411 (from 9.00 %), AB 1275 (from 7.0 %) and AB 583 (from 2.5 % to 43 %, cereals and cereal products) go beyond this range — there the standard gives no precision data. Edition: AB 583 cites PN-ISO 6540:1994, i.e. the text of ISO 6540:1980 — ISO 6540:2021 revised the procedure, the expression of results, precision, notes and test report of both methods (former clauses 7–10 and 17–20) and the annexes; in public intervention Regulation 2016/1240 requires the latest version of the standard. The dry matter at AB 583 is a quantity calculated from the moisture result, not a separate measurement. For cereals other than maize this standard does not apply — the moisture content of other cereal grains is described in the entry on PN-EN ISO 712-1 (reference method for cereal grains and cereal products).

WHAT WE DO NOT GIVE. The fragment of ISO 6540:2021 we read (iTeh preview) covers the foreword, the introduction and clauses 1–4 (up to point 4.9 — test report). We do not give the course of the routine method (clause 5: drying time in the 2021 edition, mass of the test portion, formulae, precision), the absolute method (Annex A), the results of the interlaboratory test, including the reproducibility standard deviation sR and the reproducibility limit R (Annex B), Table B.3 or Annex C. We did not compare the text of ISO 6540:1980 with the 2021 edition — we know only the list of revised clauses from the foreword. We did not check whether EN ISO 6540:2021 is current at CEN, or whether ISO 24333:2009 has a newer edition. We did not check the status of EN 15948, ISO 5725-2 or of the Czech standards. We did not check references to the standard in Polish legislation.

Method principle

Moisture content is the loss in mass of a maize sample under specified conditions. In the reference method a sample with a moisture content outside 9.00–15.00 % is first conditioned at 60–80 °C or in the laboratory air, then about 30 g is ground, and two test portions of about 8 g are dried for 4 h ± 5 min at 130–133 °C and weighed after cooling in a desiccator; result — mean of two determinations as a percentage by mass of the product as received, corrected for the water lost during conditioning (ISO 6540:2021, points 4.1–4.6). The routine method dries whole grains without grinding and gives results biased high by about 0.30 % (introduction; we did not read the course of clause 5).

Applications

• Maize grains, ground whole maize, groats, grits and maize flour — reference method (clauses 1 and 4)
• Whole maize grains — routine method, not for experts’ reports or for the calibration and checking of moisture meters (clauses 1 and 5)
• Public intervention: standard method for determining the moisture content of maize, binding in disputes (Implementing Regulation (EU) 2016/1240, Annex I Part II point b)
• In accreditation scopes: 6 Polish laboratories — maize grain in ranges from 7.0 % to 40.00 %, and in one item cereals and cereal products (2.5–43) %

Key parameters

Standard

Standard number

PN-EN ISO 6540:2021-08 (English version; adopts EN ISO 6540:2021 and ISO 6540:2021 [IDT])

Title (PL)

Kukurydza — Oznaczanie wilgotności (rozdrobnionego i całego ziarna)

Title (EN)

Maize — Determination of moisture content (on milled grains and on whole grains)

Step-by-step procedure

1. Receipt and assessment of the sample

   Representative sample, in a sealed package, undamaged (point 4.3; sampling — ISO 24333 recommended); checking whether the product needs grinding (particles ≤ 1.7 mm, < 10 % over 1 mm, > 50 % below 0.5 mm — no grinding) (point 4.4.1).

2. Conditioning and grinding

   Moisture 9.00–15.00 %: grind about 30 g immediately. Above 15.00 %: about 100 g weighed to the nearest 0.1 g in the boat (m2), oven 60–80 °C to 9.00–15.00 %, standing ≥ 2 h under a sheet of paper, weighing (m3), quick grinding of about 30 g. Below 9.00 %: about 100 g in the laboratory atmosphere until within that range (point 4.4.2).

   🌡 Temperature: 60–80 °C

3. Test portions

   Two capsules tared to the nearest 0.001 g (t); quickly about (8 ± 1) g each to the nearest 0.001 g (m′0) (points 4.5.1–4.5.2).

4. Drying and weighing

   Open capsule with lid in the oven; no wet samples placed in an oven with test portions at the end of drying and no opening of the door; then cover quickly, desiccator (dishes not on top of one another), after cooling (generally 30–45 min) weighing to the nearest 0.001 g (m′1) (points 4.5.3–4.5.4).

   ⏱ Time: 4 h ± 5 min • 🌡 Temperature: 130–133 °C

5. Calculation and result

   Formula (1) without conditioning or Formula (2) with masses m2 and m3; mean of two results if the difference ≤ r = 0.19 (otherwise repeat), to two decimal places; test report with reference to ISO 6540 (points 4.6, 4.7.2, 4.9). PN-EN ISO 6540:2021-08 — current (PKN card as of 07.11.2026; English version).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Ovens at 130–133 °C and hot capsules — protection of hands against burns (general rule; the fragment of the standard we read has no clause on safety)
• TECHNICAL NOTE: the routine method on whole grains gives results biased high by about 0.30 % and is not suitable for experts’ reports or for the calibration and checking of moisture meters (clause 1, introduction)
• TECHNICAL NOTE: with conditioning the result is calculated with Formula (2) — Formula (1) would give the moisture of the pre-dried sample, not of the maize as received (point 4.6)

Frequently asked questions