Food packaging
In fixed-weight prepack control, the goal is not to have packages that are all identical to the gram, but to ensure that the declared quantity on the label is respected according to precise batch and tolerance rules.
When we talk about fixed weight (or nominal quantity) in the food industry, the basic rule is simple: the consumer must receive the quantity declared on the label, taking normal production variability into account.
European legislation on prepackages therefore allows small deviations, but within clearly defined limits: what matters is the batch average, the number of packages below threshold, and above all the fact that no single unit may fall below an absolute limit.
What Nominal Quantity (QN) means
The QN is the value declared on the label: for example 200 g, 500 g or 1,000 ml. It is the reference value used to calculate the permitted tolerances.
The correct principle is not that “every single package must weigh exactly what is indicated”, but rather that the batch must be compliant and any negative deviations must remain within the permitted limits.
The 3 key rules to remember
1
Batch average ≥ QN
For every batch checked, the average actual content must not be lower than the declared nominal quantity.
2
Small deviations are allowed
Some units may be below QN, but only within the permitted negative tolerance threshold, called TU1.
3
Never below TU2
The second threshold, TU2, is equal to 2 × TU1: below this limit, even a single unit is non-compliant and must be rejected.
In practical terms
The two abbreviations to remember are:
- TU1 = maximum permitted negative tolerance
- TU2 = absolute limit, equal to 2 times TU1
The correct logic is therefore: compliant average + few units below TU1 + no units below TU2.
Quick formula
For a product with a declared QN:
TU2 = 2 × TU1
If a package falls below TU2, it cannot be placed on the market.
Clear table: how to interpret the thresholds
One of the most common points of confusion is how to read the thresholds. Below you will find a practical, unambiguous table designed to clearly distinguish the three operating areas.
| Zone | Package weight | Meaning | Practical action |
|---|---|---|---|
| Compliant | ≥ QN − TU1 | The unit falls within the ordinary permitted tolerance. | The package is acceptable, provided that the batch average remains ≥ QN. |
| Attention zone | < QN − TU1 but ≥ QN − TU2 | The unit exceeds the first tolerance threshold, but does not yet go beyond the absolute limit. | It must remain a very limited share of the batch; it requires statistical control and process monitoring. |
| Non-compliant | < QN − TU2 | The unit is beyond the absolute permitted limit. | It must be rejected: it cannot be placed on the market. |
Compliant Attention zone Non-compliant
Practical example: QN = 200 g
In the case of a package with QN = 200 g, the example uses the following values: TU1 = 9 g and TU2 = 18 g.
This means:
- Compliant if the unit weighs 191 g or more
- Attention zone if the unit is between 182 g and 191 g
- Non-compliant if the unit falls below 182 g
Visual chart of the thresholds — example with QN 200 g
182 g 191 g 200 g QN − TU2 QN − TU1 QN NON-COMPLIANT ATTENTION COMPLIANT Reject Limited share in the batch Acceptable
Simple reading: below 182 g the package is non-compliant; from 182 g to 191 g it requires attention; from 191 g upwards it falls within the ordinary tolerance. Key point to remember: the chart helps you read the single unit, but true compliance must always be assessed at batch level as well. So it is not enough to look at one single weight: you also need to verify the overall average and the share of packages in the attention zone.
Common mistakes to avoid
- thinking that all packages must always be exactly equal to the declared QN;
- confusing TU1 with TU2;
- not distinguishing between single-unit control and batch control;
- using tables with overlapping rows or poor readability;
- not recording process data and therefore failing to intercept drift and giveaway in time.
Practical checklist for the packaging department
To manage fixed weight properly, it is useful to follow a simple and repeatable procedure.
1. Define the QN Clearly establish the weight or volume declared on the label. 2. Define the batch Same product, same QN, same packaging and homogeneous filling conditions. 3. Use the correct instruments Suitable measuring instruments and scales, verified and properly maintained. 4. Set up production controls Full weighing or statistical sampling, depending on the production process. 5. Manage tare correctly If control is carried out on the closed package, reliable packaging weight data are required. 6. Record and correct Keep the results, analyse deviations and intervene when variability or giveaway increases.
Conclusion
Fixed weight is not just a matter of weighing, but of method. The three rules to remember are always the same:
- batch average ≥ QN
- only a limited share of units below TU1
- no units below TU2
If these three points are under control, the process becomes much more robust and compliance much easier to manage every day.
