A reliable analysis starts with the right sampling
In the food industry, automatic systems are increasingly used to sample powdered raw materials and end products. This reduces manual handling, increases reproducibility and makes quality control more efficient.
Yet one question remains essential: does the collected sample actually represent the entire product batch?
An automatic sampler can function perfectly from a technical point of view and still give a distorted picture if the sampling is not well designed. With powders in particular, segregation, particle size and differences in density play an important role.
For QA managers and quality staff, it is therefore important to substantiate and validate not only the analytical method, but also the sampling itself.
Which standards are relevant for powder sampling?
There is no single universal international standard that applies to every type of powder sampling. Depending on the product, the application and the quality characteristic, various guidelines are available. The main references are:
| Standard or guideline | Application |
|---|---|
| Codex CXG 50-2004 | General guidelines on sampling of foods |
| ISO 707 / IDF 50 | Sampling of milk and dairy products, including powders |
| ISO 14488 | Sampling and sample preparation of fine- and coarse-grained materials |
| ISO 2859-1 | Sampling plans for inspection by attributes |
| ISO 3951 | Sampling plans for inspection by variables |
| FDA BAM Chapter 1 | Sampling and sample preparation for microbiological analyses |
The choice of standard must match the product and the specific analysis. For a QA manager working with milk powder, food ingredients or other powdered end products, it is advisable to state the applicable reference explicitly in the Sampling SOP.
The two golden rules of powder sampling
When sampling powders, two principles are particularly important.
1. Sample from a moving product stream
A sample taken only from the top of a silo or container does not necessarily represent the entire contents. During storage, conveying and filling, powders can segregate. Fine and coarse particles, as well as particles with different densities, can separate from each other.
As a result, the composition at the top of a silo can differ from that at the bottom. A sampling point in a moving product stream therefore often provides a better basis for representative sampling.
2. Take many small increments across the full product stream
One large sample at one specific moment can contain random deviations. A better method is to collect several small increments during production, preferably sampling the full cross-section of the product stream each time.
These increments can then be combined into one composite sample. This limits the influence of local deviations and gives a more reliable picture of the product batch.
How do you validate an automatic powder sampler?
A common mistake is to assume that an automatic sampler is reliable because it was built to technical specifications. The real question is whether the system collects representative samples.
A practical validation method is to compare automatic sampling with manual reference sampling. Over several production batches, two methods are applied side by side:
- Automatic sampling with the installed system.
- Manual sampling by full cross-cuts of the product stream.
The results are then compared for relevant product specifications, for example:
- Moisture content.
- Particle size distribution.
- Fat content.
- A specific ingredient or component marker.
The results must fall within predefined acceptance criteria and the relevant measurement variability. Also document the position of the sampler, the quantity per increment, the sampling frequency and how increments are combined. This gives a well-founded validation that can also be explained during an SQF or other quality system audit.
Why closed sampling is becoming more important
Besides representativeness, hygiene is an important point. An open sampling point or a manually opened sample port can lead to contamination of the product and the environment. This risk increases when several raw materials or product batches pass through the same installation.
A closed sampling solution can help limit these risks. Consider:
- Closed sampling points in conveying lines.
- Sampling directly during discharge.
- Suitable connections for closed sample bags.
- Minimising manual handling.
- Product contact parts that are easy to inspect and clean.
The sampling facility must be included in the hygiene plan and the risk assessment of the installation.
Powder handling and quality assurance start with design
At Hecht Technology we look at powder handling from the perspective of the complete production process. The choice of a discharge station, conveying system or silo affects more than capacity and productivity. Segregation, representative sampling, hygiene and dust control also deserve attention.
By taking these aspects into account during design, quality problems can be prevented before they occur in production.
Conclusion
An automatic powder sampler is only reliable once the representativeness of the sample has been demonstrated. The two key principles are sampling from a moving product stream and collecting several small increments across the full stream. Comparison with a reference method and a closed sampling concept further strengthen quality assurance.