Yeast and Mold Counting — ISO 21527-1 / ISO 21527-2

What Is Yeast & Mold?

Yeast and mold counting is the determination of the number of fungal microorganisms that can grow in the sample. The method varies depending on the water activity of the product: ISO 21527-1 is applied for products with high water activity, and ISO 21527-2, which uses selective media, is applied for products with low water activity (dry).

Purpose of Yeast & Mold

The aim is to determine the level of yeast and molds that cause spoilage and to predict product quality throughout its shelf life. Additionally, mold growth is a sign of mycotoxin risk.

Which Products Is Yeast & Mold Applied To?

Bakery products and bread
Nuts and dried fruit
Cheese and dairy products
Juice and concentrates
Spices and grain products

In Which Sectors Is Yeast & Mold Used?

FoodAgricultureRetail

Standards Related to Yeast & Mold

TS ISO 21527-1 (yeast and mold counting in products with high water activity)
TS ISO 21527-2 (yeast and mold counting in products with low water activity)
TS EN ISO 6887 series (sample preparation)
TS EN ISO 7218 (genel kurallar)

Yeast & Mold Conditions

Method selection: According to the water activity of the product; wrong section gives wrong result
Incubation: At standard defined temperature and time
Census: Intermediate counting can be done during incubation.

Equipment for Yeast & Mold

Sterile cabinet and incubators
water activity meter
Autoclave and medium preparation
Colony counter

Sample Requirements for Yeast & Mold

The sample must be sent unopened and in its original packaging, maintaining the cold chain. Whether the sampling method is representative of the batch determines the validity of the result; The result from a single unit is not enough to make a decision about the party.
If water activity value is unknown, it should be measured
Areas that appear moldy can also be sampled
Sample quantity is determined according to the sampling plan

Duration of Yeast & Mold

Yeast and mold incubations are longer than bacterial counts; The result cannot be given before the time defined in the standard is completed.

Yeast & Mold Procedure

1The water activity of the sample is determined and the appropriate standard fraction is selected.
2The sample is prepared and diluted aseptically.
3Broadcast planting is done on suitable medium.
4It is incubated at defined temperature and time.
5Yeast and mold colonies are counted separately.
6The result is calculated as cfu/g or cfu/mL.

Yeast & Mold Acceptance Criteria

Acceptance criteria are microbiological criteria defined on a food category basis in (EU) 2073/2005. The regulation distinguishes two types of criteria: the food safety criterion (can the product be placed on the market) and the process hygiene criterion (is the production process under control). Which one applies depends on the product category and is confirmed by the text of the applicable regulation.

Evaluation of Results

Yeast and mold are reported separately because they refer to different problems: yeast mostly refers to fermentation and gas formation, while mold refers to surface degradation and mycotoxin risk. If mold counts are high, mycotoxin analysis should be evaluated.

Yeast & Mold Report

Sample description and water activity
Standard section and medium applied
Incubation conditions
Yeast and mold results separately
Measurement uncertainty

Accreditation

EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.

Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.

Scope and authorisations

Related Regulations

(EC) 2073/2005 Microbiological Criteria Regulation
Food Hygiene Regulation (EC) 852/2004

Food Testing — What Does This Testing Field Cover?

The section below describes the field that the Yeast & Mold test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.

Food testing shows that a product is safe for consumption and contains what its label states. The family works along three axes: microbiological safety, chemical safety and nutritional composition. All three require different laboratory infrastructure, a different body of methods and a different turnaround time.

The most distinctive feature of the field is TIME PRESSURE. A steel specimen can wait on a shelf; a raw milk or fresh meat sample cannot. The time the sample was taken, the transport temperature and how long it takes to reach the laboratory directly determine the validity of the result. In food microbiology the cold chain record is therefore an inseparable part of the test report.

On the microbiological side there are two different questions and they must not be confused. DETECTION of a pathogen is a qualitative question: is Salmonella present in the sample or not? ENUMERATION of indicator organisms is a quantitative question and an indicator of production hygiene. The absence of a pathogen in a product does not show that hygiene is good; if the total mesophilic aerobic count is high, there is a problem in the process.

On the chemical side, pesticide residues, mycotoxins, heavy metals, additives, veterinary drug residues and process contaminants (acrylamide, furan, PAH) are measured. Multi-residue methods in this area (QuEChERS-based LC-MS/MS and GC-MS/MS) can screen hundreds of active substances in a single analysis; limits are defined separately for each product–substance pair.

On the composition side, protein, fat, moisture, ash, fibre, sugar profile, fatty acid composition, vitamin and mineral content are determined. These values are the basis of the nutrition declaration on the label and the tolerance ranges are defined in legislation — the difference between the declared value and the measured value must stay within that tolerance.

There is NO CE marking on food, and this shapes how the field works. Conformity is demonstrated through operating a HACCP-based food safety system, complying with labelling rules and not exceeding contaminant, residue and microbiological limits. A test result produces evidence not for a certificate but for a functioning system.

Allergen management carries particular weight. The presence of an undeclared allergen in a product is one of the most frequent causes of food recalls. Analysis here runs together with cleaning validation: it is shown that the line has been cleaned adequately after a production run containing an allergen and that the risk of cross-contamination is under control.

Voluntary schemes have become effectively mandatory in this field. Retail chains require their suppliers to hold a certificate under a GFSI-recognised scheme (BRCGS, IFS, FSSC 22000); without it, getting onto the shelf is practically impossible.

Method groups in this field

Pathogen detection
Detection of Salmonella, Listeria monocytogenes, Campylobacter, Cronobacter and Shiga toxin-producing E. coli; culture-based and molecular methods.
Indicator counts
Total mesophilic aerobic count, Enterobacteriaceae, coliforms and E. coli, coagulase-positive staphylococci, yeasts and moulds, lactic acid bacteria, sulphite-reducing Clostridia.
Pesticide and veterinary residues
Multi-residue screening by LC-MS/MS and GC-MS/MS with QuEChERS extraction.
Mycotoxins and contaminants
Aflatoxins, ochratoxin A, deoxynivalenol, patulin; heavy metals (ICP-MS), acrylamide and PAH compounds.
Nutritional composition
Kjeldahl protein, fat and fatty acid profile, moisture, ash, dietary fibre, sugar profile, vitamin and mineral analyses.
Allergens and authenticity
Gluten, milk, egg, nut and soy allergen analyses; molecular methods for species identification and adulteration detection.

Commonly confused in this field

Sampling is half the result. A sample transported at the wrong temperature or delayed gives an invalid result even if it is analysed correctly in the laboratory.
The absence of a pathogen does not show that hygiene is good; indicator counts give separate information and the two are read together.
A result from a sample taken from a lot can be generalised to the whole lot only if the sampling plan was set up statistically.
Limits are defined in separate regulations by product group and are updated regularly; a conformity decision based on an outdated limit table may be wrong.
For exports, the limits of the destination country may differ from EU limits; the same product may be compliant in one market and non-compliant in another.

Which decisions these results support

Verification of the HACCP plan and process monitoring
The basis for the nutrition declaration and allergen information on the label
Health certificates before export and compliance with destination market limits
Supplier and lot-based acceptance control
Shelf-life studies and determining storage conditions
Producing evidence for audits under GFSI-recognised schemes

Related Tests

Frequently Asked Questions About Yeast & Mold

We saw mold but the count was low, why?

Mold is distributed unevenly throughout the product; While visible mold may be concentrated in one spot, the sample may have been taken from another spot. If there is visible deterioration, that area should be sampled separately.

If there is mold, are there mycotoxins?

Not necessarily. Not all molds produce mycotoxins, and those that do do not produce them under all conditions. However, mold growth is a risk indicator and calls for relevant mycotoxin analysis.