🦠 Yeasts and moulds in food, feed and swabs — colony count technique at 25 °C: plates with a specified selective medium inoculated with the sample and its tenfold dilutions, aerobic incubation for 3, 4 or 5 days, number of yeasts and moulds per gram or millilitre; PN-ISO 7954:1999 (withdrawn standard)

Microbiology PN-ISO 7954

Overview

WHAT THE STANDARD COVERS. The "Scope" field of the PKN card, in full: "The method described consists in preparing plates with a specified selective medium and inoculating them with an appropriate quantity of the test sample, and preparing further plates inoculated with tenfold dilutions of the sample. The plates are then incubated under aerobic conditions at 25 degrees C for 3, 4 or 5 days, and the number of yeasts and moulds per gram or millilitre of the sample is calculated from the number of colonies on selected plates from the dilutions giving a significant result" (our translation; no full stop at the end on the card). The description of ISO 7954:1987 in the Standard Norge catalogue speaks of poured plates. The card does not name the medium or say how colonies are told apart; we did not have the text of the standard (7 pages).

STATUS (cards as of 13.10.2026). The card of PN-ISO 7954:1999 (Polish version) bears the heading "Withdrawn and replaced by PN-ISO 21527-1:2009 - Polish version": publication 02-09-1999, "Withdrawal date: 08-06-2009", 7 pages, price group D, Food, Agriculture and Forestry Sector, KT 3 Food Chain Microbiology, "Adopts: ISO 7954:1987 [IDT]", ICS 07.100.30. The successor, PN-ISO 21527-1:2009 "Microbiology of food and animal feeding stuffs — Horizontal method for the enumeration of yeasts and moulds — Part 1: Colony count technique in products with water activity greater than 0.95" (publication 08-06-2009, 13 pages, adopts ISO 21527-1:2008 [IDT], "Replaces: PN-ISO 7954:1999"), bears the heading "Withdrawn" and "Withdrawal date: 25-09-2020", with no "Replaced by" field. The second part, PN-ISO 21527-2:2009 (products with water activity less than or equal to 0.95; "Replaces: PN-ISO 7698:2004"), was also withdrawn on 25-09-2020. The PKN search under "21527" (13.10.2026) returns only these two withdrawn parts — there is no current Polish standard in this chain. At the publisher: according to the Standard Norge catalogue (13.10.2026), ISO 7954:1987 (edition 1 of 15 October 1987, ISO/TC 34/SC 9) has the status "Withdrawn" dated 1 July 2008 and the notes "Revised by: ISO 21527-1:2008" and "Revised by: ISO 21527-2:2008"; ISO 21527-1:2008 has the status "Published" there.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database from the production server, refreshed on 12.10.2026). Number 7954 appears in 16 records at 10 laboratories, always in the form "PN-ISO 7954:1999" (at AB 819 in two records with the addition "+ I 15/PN-ISO 7954:1999 edition 2 of 01.09.2016"). In the current PCA documents (read on 12–13.10.2026; issues from 30.10.2025 — AB 452 — to 01.10.2026 — AB 438) the number appears in 13 rows at the same 10 laboratories; a search of all downloaded PCA documents found no laboratories outside the database copy, and no pages are repeated in any document. No row with the number is set in bold italics; in the AB 438 document (issue of 01.10.2026) a suspension at the laboratory's request covers other entries. The "Laboratories" tab (search term "PN-ISO 7954") shows all 10 laboratories — checked with the tab query on the labcoda.pl production server on 13.10.2026.

WHAT THE LABORATORIES TEST (database copy and PCA documents). Test object: food with long lists of groups (meat and meat products, milk and dairy products, fish, fruit and vegetables and their products, confectionery, cereals, spices, oils and fats, food concentrates, beverages, frozen food, ready meals) — AB 079, AB 313, AB 438, AB 452, AB 462, AB 510, AB 819, AB 1164; feed — AB 079 ("feed and pet food"), AB 313 and AB 462; food additives — AB 313 (separate entry), AB 462, AB 510; "Products with water activity aw ≤ 0.6, milk, spices, herbs, additives, flour, dried and freeze-dried products" — AB 483; surface swabs — AB 462 (environmental samples from the food production and trade area, in the same entry as food), AB 492 (environmental samples from technical surfaces: swab from a surface delimited by a template and from a surface not delimited) and AB 819 (environmental samples from food production and trade areas, separate entry). Characteristic: number of yeasts and moulds (at AB 079 "at 25°C"), at AB 510 also the number of yeasts and the number of moulds separately, at AB 819 only separately. Technique: colony count technique (pour plate) — 14 records; colony count technique (spiral surface plating) — 2 records of AB 819 (food, with instruction I 15).

ALONGSIDE THIS STANDARD. In the database copy, yeasts and moulds are enumerated by 58 laboratories (entries with "yeasts" or "moulds" in the test description or parameters, without cosmetics, pharmaceutical and medical products, air, waste water, and drinking or swimming-pool water); PN-ISO 21527-1 is cited by 37 of them, PN-ISO 21527-2 by 35, this standard by 10. Eight of the ten laboratories with this standard also have PN-ISO 21527-1 or PN-ISO 21527-2 in other entries (AB 079, AB 313, AB 452, AB 462, AB 483, AB 492, AB 510, AB 819); AB 438 and AB 1164 enumerate yeasts and moulds only according to this standard. At AB 079 the row with this standard stands directly below the row "Number of yeasts and moulds in products with water activity less than or equal to 0.95 — PN-ISO 21527-2:2009". Both parts of PN-ISO 21527 are described in separate Knowledge Base entries.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. First — status: the standard has been withdrawn since 2009, and the successor named on its card since 2020; there is no current Polish Standard in this chain, and ISO replaced ISO 7954 with two parts of ISO 21527. Second — water activity: the successors divide products into two groups (water activity greater than 0.95 — part 1; less than or equal to 0.95, including dried fruit, cereals, flours, nuts, spices and additives — part 2), while the card of this standard contains no such division; AB 483 applies it precisely to products with water activity ≤ 0.6, dried products and flour. Third — plating: the ISO description speaks of poured plates, while AB 819 plates food on the surface with a spiral plater according to its own instruction I 15 — a deviation from the description in the standard. Fourth — result: the card speaks of the number of yeasts and moulds per gram or millilitre of sample; how to express the result for a surface swab (AB 462, AB 492, AB 819) and how to report yeasts and moulds separately (AB 510, AB 819) does not follow from the card.

WHAT WE DO NOT GIVE. We did not have the text of the standard — we do not give the name and composition of the selective medium, the diluent, the inoculum volume, how yeast and mould colonies are told apart, the criteria for choosing plates for counting, the calculation formula or precision.

Method principle

An appropriate quantity of the sample and its tenfold dilutions are inoculated onto plates with a specified selective medium (according to the ISO description — poured plates), incubated under aerobic conditions at 25 °C for 3, 4 or 5 days, and the number of yeasts and moulds per gram or millilitre of the sample is calculated from the number of colonies on the plates of the dilutions giving a significant result (PKN card). WE DO NOT GIVE the medium or details — we did not have the text of the standard.

Applications

• Food — number of yeasts and moulds (withdrawn standard in the current accreditation scopes of 10 laboratories)
• Feed and food additives — entries at AB 079, AB 313, AB 462, AB 483 and AB 510
• Swabs from technical surfaces and from food production areas — entries at AB 462, AB 492 and AB 819

Key parameters

Standard

Standard number

PN-ISO 7954:1999

Title (PL)

Mikrobiologia — Ogólne zasady oznaczania drożdży i pleśni — Metoda płytkowa w 25 stopniach C

Title (EN)

Microbiology — General guidance for enumeration of yeasts and moulds — Colony count technique at 25 degrees C

Step-by-step procedure

1. Dilutions

   Inoculation of an appropriate quantity of the sample and its tenfold dilutions (PKN card). PN-ISO 7954:1999 withdrawn on 08-06-2009 (card as of 13.10.2026).

2. Inoculation

   Plates with a specified selective medium; according to the ISO description — poured plates (Standard Norge).

3. Incubation

   Aerobic conditions, 25 °C, 3, 4 or 5 days (PKN card).

4. Counting and result

   Number of yeasts and moulds per gram or millilitre of sample from plates of dilutions giving a significant result (PKN card); WE DO NOT GIVE the criteria or the formula.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Work with fungal cultures — rules of work in a microbiology laboratory
• SUBJECT-MATTER NOTE: the standard and the successor named on its card, PN-ISO 21527-1:2009, are both withdrawn; ISO replaced ISO 7954 with two parts of ISO 21527

Frequently asked questions