The savory snack weighing process presents characteristics that clearly distinguish it from other food sectors. The product is light, the packaging is inflated with inert gas, the lines operate at high speeds and the environment is dry but filled with salt and flavoring powders.
These conditions test both the measuring instrument and the way it is installed and managed.
Before even choosing the instrument, however, it is necessary to clarify a point that determines the entire control architecture: is the savory snack sold by nominal quantity or variable weight?
The necessary instrument, the applicable regulations, the parameters to be verified during the purchase phase and the periodic verification obligations depend on the answer. It is a distinction that in the dry sector is taken for granted more often than it should be.
Why savory snack weighing requires a dedicated approach
Many of the indications valid for dairy, meat or fruit and vegetables do not transfer directly to the snack sector. There are five variables that change.
Low unit weight. Typical formats range from 25 g for single-portion to 200 g for family size. The permitted tolerances, expressed in absolute value, are a few grams: the instrument resolution must be proportionate to the format, not simply adequate for the declared maximum capacity.
Protective atmosphere packaging. Nitrogen performs two functions: it protects the unsaturated fats typical of fried products from oxidation and mechanically cushions a fragile product. The result is a package with high volume and very low density, exposed to air flows and unstable on the conveyor belt. On a vacuum-packed meat line, this problem simply does not exist.
High line speeds. Vertical packaging machines usually work between 80 and 200 packs per minute per line, fed upstream by multihead weighers. The weight check system must sustain that pace without becoming the line bottleneck.
Dry but aggressive environment. There are no high-pressure washdowns as in dairy or meat, but salt (hygroscopic and corrosive), flavoring powders and oily residues. Cleaning typically takes place dry, with suction and compressed air. An IP65 rating is generally sufficient, while IP69K, indispensable in other food sectors, represents an over-dimensioning here with a cost impact that finds no operational justification.
Thermal instability of the product. The product comes out hot from the fryer or oven and must reach a stable temperature before packaging. Hot packaging generates internal condensation and weight drifts that compromise measurement repeatability, with an effect that adds to the normal filling variability.
Nominal quantity or variable weight: two different control logics
In the vast majority of cases, the savory snack is a pre-package with a pre-determined nominal quantity. The price is already printed on the film during the printing phase and does not depend on the weight of the individual package. The control therefore does not serve to determine a commercial value, but to demonstrate that the content respects the quantity declared on the label.
Italian regulations on pre-packages set three conditions for the application of the “e” mark:
- the actual average content of the batch must not be less than the nominal quantity;
- pre-packages with a negative error greater than the permitted negative tolerance (TNE) must not exceed 2.5% of the batch;
- no pre-package may have a negative error greater than double the TNE.
The TNE varies according to the nominal quantity: 9% for packages between 5 and 50 g (therefore 2.25 g on a 25 g format), fixed 4.5 g between 50 and 100 g, 4.5% between 100 and 200 g (6.75 g on a 150 g format), fixed 9 g between 200 and 300 g.
The instrument that verifies these conditions directly on the line, package by package, is the checkweigher. Its task is not to calculate a price, but to classify each unit with respect to acceptance thresholds and feed the batch statistics.
The variable weight also exists in dry food, but in specific niches: nuts and dried fruit repackaged in trays, savory baked products sold by weight, artisanal snacks, packaging at the point of sale. In these cases, the commercial value actually depends on the weight of the individual unit and an integrated weigh price and labelling solution is needed, which weighs, calculates the price and prints the label in a single cycle. The operation of these systems and their technical characteristics are covered in two dedicated in-depth studies.
Confusing the two regimes is the most expensive mistake that can be made during the specifications phase, because it leads to specifying an instrument that solves a different problem from the real one.
The regulatory framework: automatic instruments and periodic verification
Both the checkweigher and the weigh price labeller belong to the family of automatic weighing instruments, subject to European metrological regulations on measuring instruments. The CE marking is accompanied by a supplementary metrological marking that certifies its suitability for use with legal validity.
The multihead weigher that fills the packages upstream also falls under automatic instruments, as a gravimetric filling machine. These are different pieces of equipment with similar obligations, and it is advisable to treat them together during the project phase rather than addressing them separately once the plant is started.
The operational distinction is this: when the instrument is used exclusively for internal process control and its results have no commercial or legal relevance, metrological marking is not required. When, instead, the weighing determines a commercial value or is used to demonstrate pre-package compliance, the instrument is subject to metrological marking and periodic verification according to current regulations.
It is worth clarifying this point during the specifications phase, because it has a practical consequence: an investment in an instrument that is not metrologically verifiable becomes a constraint if the intended use changes later, for example when a large-scale distribution customer requires documentary evidence of the weight check.
The technical parameters that really matter
Declared speed and real speed. A figure of 250 packages per minute must always be read together with the weight and length of the package on which it was measured. That value does not automatically transfer from a 25 g single-portion to a 200 g family size. Always ask which format the declared performance refers to.
Verification scale division and accuracy class. On light packages, a fine scale division is needed. The value to be compared is that of the verification scale division associated with the maximum capacity, not the internal resolution of the instrument, which is a processing figure and not a metrological parameter.
Weighing belt geometry. Only one package at a time must be on the load cell. Long formats require longer belts and greater distances between packages, with a direct impact on the maximum speed actually achievable. It is the constraint that most often explains the gap between declared performance and obtained performance.
Signal filtering. Inflated packages generate oscillations during transit. High sampling frequency and adaptive digital filters are needed: a filter that is too aggressive lengthens the measurement time and reduces speed, one that is too light lets noise through and generates false positive rejects, i.e. compliant product expelled without reason.
Protection from air flows. This is a specific criticality of this sector. Shielding casings and positioning away from ventilation vents, doors and cooling fans affect repeatability more than is usually estimated during the layout phase.
Ejection system. On light and fragile products, an air blast is preferable to a mechanical pusher, which can deform or damage the package and compromise its seal. A reject confirmation sensor must always be provided to prevent a non-compliant package from continuing towards the end of the line.
Where margin is recovered: the reduction of overfilling
The multihead weigher, to simultaneously respect the three rules of pre-packages, tares the filling to an average value higher than the nominal quantity. That overfilling is product given away, and on industrial volumes it becomes a significant cost item.
A calculation example, purely illustrative: a line at 120 packages per minute, on two 8-hour shifts, for 220 days a year, produces about 25 million packages. Reducing the average overfilling by just one gram means not giving away about 25 tons of product in a year.
The interesting point is that the reduction margin does not depend on the line speed, but on the dispersion of the filling distribution. The more the standard deviation is contained, the more the average target can approach the nominal quantity while continuing to respect the three rules. It follows that reducing variability is worth exactly as much as lowering the target: maintenance and calibration of the multihead heads, dimensional stability of the product, humidity control and consistency of the packaging temperature are all interventions that act on the same lever.
This is where the checkweigher stops being a simple filter and becomes a process tool: by returning the average and standard deviation to the multihead weigher in real time, it closes a feedback loop that allows working closer to the nominal quantity while maintaining the regulatory safety margin.
Errors to avoid when choosing the weight check system
The first error is choosing the instrument before having defined the sales regime. Specifying a weigh price labeller for a nominal quantity line means purchasing a price calculation function that will never be used, neglecting the statistical functions that are actually needed.
The second error is reading the declared speed without the reference format. A performance measured on a short and heavy format does not describe the behavior of the machine on the family size, which is often the most critical for the line.
The third error is leaving the filling target unchanged over time. Many plants work with a value set years before, with a margin of prudence that has never been questioned despite maintenance interventions and process improvements.
The fourth error is underestimating the physical environment around the instrument. Air flows, vibrations transmitted by the frame and non-isolated supports generate instabilities that are attributed to the load cell when the cause is upstream.
The fifth error is not verifying the metrological intended use. An instrument purchased for process control only may need to be transformed into a compliance instrument when the sales channel or the final customer changes.
When to request a technical evaluation
A preliminary technical evaluation becomes particularly useful when the line works at high speeds, manages many different formats with frequent changes, or when the average overfilling has never been systematically measured. These are the conditions in which the gap between theoretical performance and real performance tends to be wider.
If you are evaluating an intervention on an existing line, the most useful starting point is almost always the same: collect two weeks of real weighing data and observe the distribution. Very often the problem is not the instrument, but a target set with too much prudence and never reviewed again.
The integration of weight check data with line systems passes through weighing terminals. To learn more about the available solutions, you can consult the page dedicated to checkweighers or contact Coop Bilanciai for an evaluation of the specific application.
FAQs
Is a weigh price labeller needed for savory snacks?
In most cases, no. Savory snacks are pre-packages with a nominal quantity with the weight already printed on the film. The correct instrument is the checkweigher. The weigh price labeller is only needed in variable weight niches, such as repackaged nuts.
What tolerance applies to a 100 gram package?
The permitted negative tolerance is 4.5 grams. A maximum number of packages equal to 2.5% of the batch is allowed to exceed the threshold up to the maximum value equal to double, i.e. 9 grams. The average content of the entire batch cannot in any case fall below 100 grams.
Must the checkweigher have the M marking?
It depends on the use. If it is only needed for internal process control, it is not required. If the results are used to demonstrate pre-package compliance or for commercial purposes, the instrument must be M-marked and subjected to periodic verification.
What IP protection rating is needed in snack packaging?
In a dry environment with suction and compressed air cleaning, IP65 is generally adequate.
Why are inflated packages more difficult to weigh?
The high volume and low density make them sensitive to air flows and unstable on the belt. Shielding, a belt sized for the format and adaptive digital filters that stabilize the signal without slowing down the measurement are needed.
How is overfilling reduced without risking non-compliance?
By reducing the filling dispersion, not just the target. Maintenance of the multihead heads, regular calibration and product stability tighten the distribution and allow the average value to approach the nominal quantity while maintaining the regulatory margin.