Role of Laboratories in the Milk Sampling Process

When a milk sample leaves the farm or processing plant and arrives at a testing facility, what happens to it has already been shaped – often long before collection even begins. Laboratories don’t just receive and test samples; they actively define the conditions under which those samples should be collected, preserved, and transported. This upstream involvement is what separates a reliable test result from one that is compromised at the source. Understanding how laboratories contribute to the milk sampling process reveals why accurate dairy quality assurance depends on far more than a well-equipped testing room.

The laboratory’s role begins before the sample arrives 🔗

Most people picture laboratory involvement as starting the moment a sample is handed over for analysis. In reality, ISO 707 | IDF 50 – the international standard governing milk and milk product sampling – makes clear that written sampling procedures are required by ISO/IEC 17025 when sampling is performed by laboratories. These procedures don’t just describe how to test; they set the framework for how samples should be obtained in the first place.

This means laboratories are directly responsible for producing the instructions that field personnel follow. They determine the type of containers to be used, the minimum sample sizes needed for each type of analysis, the temperature at which samples must be stored and transported, and whether preservatives may or may not be added. Dairy technology guidance confirms that testing personnel usually can, and should, participate in preparing sampling instructions – particularly regarding the number of units to be taken, the location of collection points, the volume of each sample unit, container specifications, and transport conditions to the laboratory.

Why sampling personnel and testing personnel are typically kept separate 🔗

In structured dairy quality systems, the person who collects the sample is generally not the same person who tests it. This separation is intentional. It reduces conflicts of interest, ensures objectivity, and distributes accountability across the quality chain. However, this separation does not mean the two roles operate independently of each other.

Industry practitioners describe the diagnostics chain as a sequence: the sampling plan is developed, samples are taken by operators, transferred to an internal or external laboratory for testing, and results are reported back to quality assurance teams. The key challenge in this chain, as noted in practice, is that communication between parties is not always made easy given the number of people involved. This is precisely why laboratory-defined instructions serve as the connective tissue – they standardise what each party does, even when they never interact directly.

Effective collaboration between field samplers and laboratory staff is therefore essential. According to ANAB, sampling is considered the largest single contributor to measurement uncertainty in any testing program – yet the quality assurance of sampling procedures and sample handling remains far less evaluated than the testing itself. Laboratories that invest in clear pre-sampling guidance help close this gap.

Defining sample container requirements 🔗

Container selection is one of the most technically specific areas where laboratory guidance is indispensable. The container must suit the type of analysis planned – and different tests demand different container materials, sizes, and closure types.

IS 11546:1999 (the Indian standard aligned with ISO 707) specifies that opaque containers are recommended to protect samples from photo-oxidation, particularly when fat indices are to be determined. For sensory examinations, carton boxes lined with aluminium foil or plastic-coated parchment paper are considered appropriate. In cases where fat testing or other composition analyses require minimal headspace, containers must be nearly completely filled or purged with inert gas to maintain sample integrity.

For microbiological analysis, the standard is unambiguous: samples for microbiological examination must always be taken first, using aseptic technique, in sterile containers that are pre-sealed to prevent contamination. The laboratory specifies which containers are acceptable for each test type. Field personnel selecting containers without laboratory guidance risk invalidating samples before analysis even begins.

The role of preservatives – and when not to use them 🔗

Preservatives are sometimes added to milk samples to slow biological or chemical changes during transport. However, their use is tightly controlled by laboratory directives. ISO/IDF guidance states that preservatives should normally not be added to samples intended for microbiological or sensory examination. Where preservatives are permitted for other tests, their addition must be authorised by the testing laboratory, must not interfere with subsequent analyses, and must be clearly stated on the label and in the sampling report.

For example, formaldehyde (at 40% volume, 36% weight) at 0.1 mL per 30 mL of sample is used in some chemical fat analyses but is entirely inappropriate for microbial testing – adding it to a bacteriological sample would destroy the very organisms being counted. Without laboratory-issued instructions, field personnel have no reliable way of knowing which preservative is acceptable for a given test.

Setting standards for transport conditions 🔗

Temperature control during transport is not a minor logistical detail – it directly determines whether a sample still reflects the original product when it arrives at the laboratory. The Nevada Department of Agriculture’s Food Safety Laboratory, for instance, requires that milk samples be maintained at 0.0°C to 4.4°C from collection until arrival, and must reach the laboratory within 48 hours or less. Similar standards are applied across state and national programs.

Research published by IntechOpen on the dairy processing chain confirms that milk samples using sterile containers are collected automatically from each supplier at source and delivered to a laboratory technician for detailed analysis, with the collection temperature required to be maintained at 4-6°C. When this cold chain is broken, bacterial counts can increase exponentially during transit, producing results that are unrepresentative of the original milk – and potentially leading to unjustified rejection or unsafe acceptance of product.

ISO 707 | IDF 50 further specifies that storage and dispatch conditions must ensure the sample remains essentially unaltered from the time of collection to the start of testing. During transport, samples must be protected from off-odours and direct light. When transport times are long, a separate temperature-control sample may also be taken to verify that cold chain requirements were maintained throughout transit.

Determining the number of units to be sampled 🔗

Laboratories also provide guidance on how many units need to be sampled from a lot or consignment to make results statistically valid. This is not an arbitrary decision. ISO 707 | IDF 50 references ISO 5538 | IDF 113 for determining the number of units for sampling by attributes (pass/fail inspection), and ISO 8197 | IDF 136A for sampling by variables (quantitative measurements). The required sample size may also increase based on the tests planned – a larger laboratory sample may be necessary for certain analyses, while smaller sizes are acceptable only when no analytical or statistical justification requires otherwise.

In practical terms, this means a dairy plant sampling a batch of cheese cannot simply take two units and send them for testing if the laboratory’s analytical method requires a minimum of five units for statistically sound conclusions. The International Dairy Federation (IDF), working with ISO, continuously develops and updates standards for the statistical evaluation of analytical methods – covering chemical, physical, and microbiological parameters – to ensure that results drawn from samples are both accurate and reproducible.

When poor sampling is mistaken for poor analysis 🔗

One of the most significant – and avoidable – problems in dairy quality assurance is misattributing inconsistent test results to laboratory error when the root cause is actually poor sampling. Dairy technology literature highlights this directly: different values obtained from different samples of the same consignment are unfortunately often blamed on poor analytical work or unsatisfactory methods of analysis, when the more likely cause is either improper sampling or inherent variability within the lot itself.

This misattribution has real consequences. It can lead to unnecessary audits of laboratory performance, strained relationships between samplers and analysts, and – most critically – failure to address the actual problem, which is inadequate sampling practice. ANAB’s guidance on sampling in laboratory testing reinforces this point: the quality assurance of sampling procedures and sample handling remains poorly evaluated compared to the testing itself, making it a weak link that undermines otherwise rigorous analytical work.

The solution lies in the laboratory taking an active role in preventing these failures – not by taking over the collection process, but by issuing clear, test-specific instructions that align sampling methods with analytical requirements. University of Wisconsin Veterinary Diagnostic Laboratory guidelines illustrate this well: they specify that plastic tubes with snap-on lids are preferred for milk sample collection, that Whirl-pack and Ziplock bags should not be used, and that bulk tank samples should be collected over 3-5 consecutive days for greater accuracy – all directives that originate from the laboratory’s understanding of what the tests require.

Documentation: the link between sampling and valid analysis 🔗

A sample without a complete record is, from the laboratory’s perspective, a sample with unknown history. New York State’s Circular 278 on sampling producer milk requires that all samples arriving at the laboratory be accompanied by records that include the time and date of sampling, the product type, the temperature at the point of sampling, the sampling location, and the sampler’s name or identifier. This documentation trail allows laboratory analysts to contextualise results and flag anything that may have compromised sample integrity during collection or transit.

ISO/IDF standards further specify that the sampling report should note relevant conditions such as the state of product containers, atmospheric temperature and humidity, the age of the product, the method of sterilisation used on sampling equipment, and whether a preservative was added. Together, the sampling report and the laboratory’s test report form a complete record that supports both regulatory compliance and internal quality management. Any gaps in this chain can render even technically sound analytical results difficult to defend – particularly if results are challenged in a legal or regulatory context.

The broader quality assurance picture 🔗

The laboratory’s involvement in milk sampling is, ultimately, an expression of a broader principle in quality assurance: the integrity of a test result is only as strong as the integrity of the sample. No analytical instrument, however precise, can compensate for a sample that was collected in the wrong container, stored at the wrong temperature, or drawn from an inadequately mixed tank. Industry sources reinforce that regulatory compliance, consumer safety, and brand reputation all depend on high-quality milk testing – and that begins with sampling protocols that are designed around the requirements of the laboratory, not around convenience in the field.

The International Dairy Federation frames its work on methods of analysis and sampling as fundamentally about building mutual trust across the dairy supply chain. Standardised sampling methods – developed with laboratory input – give producers, processors, regulators, and consumers a shared language for assessing milk quality. When sampling and analysis are aligned, results are reproducible, comparisons across batches and facilities become meaningful, and decisions about product safety and payment are grounded in data that can be trusted.

What do you think? Given that poor sampling is so often misidentified as poor analysis, how should dairy operations better communicate laboratory-issued sampling guidelines to field personnel? And should laboratories be more formally involved in auditing the sampling process itself – not just the results it produces?

References

1. https://cdn.standards.iteh.ai/samples/37882/0bfcc2f1e49bdd18e9d641651d/ISO-707-2008.pdf
2. https://dairy-technology.blogspot.com/2014/01/sampling.html
3. https://qualitru.com/the-process-of-sampling-and-testing/
4. https://blog.ansi.org/anab/importance-of-sampling-in-laboratory-testing/
5. https://ia800305.us.archive.org/0/items/gov.in.is.11546.1999/is.11546.1999.html
6. https://agri.nv.gov/Food/Food_Safety/Safety/Milk_and_Dairy_Safety/
7. https://www.intechopen.com/chapters/63169
8. https://cdn.standards.iteh.ai/samples/37882/0bfcc2f1e15f49e49bdd18e9d641651d/ISO-707-2008.pdf
9. https://fil-idf.org/our-work/methods-of-analysis-and-sampling/
10. https://www.wvdl.wisc.edu/wp-content/uploads/2024/04/CL-Res-59-milk-sample-collection-1.pdf
11. https://agriculture.ny.gov/circular-278-sampling-producer-milk
12. https://contractlaboratory.com/milk-testing-in-laboratories/