When a candy line starts running light, the quickest response is usually to raise the target weight. That may reduce underweight rejects, but it can also turn a process problem into permanent product giveaway.

The better approach is to separate the declared net weight, the multihead weigher target, and the checkweigher reject limits. Each has a different job. NIST Handbook 133 evaluates finished packages through a defined sampling procedure, not from the filler display alone.

Why a Good Weigher Reading Can Still Produce a Light Bag

A multihead weigher measures the candy dose before it enters the bag. The net quantity declaration applies to the finished package that reaches distribution.

Between those points, gummies may remain on a chute, hard candies may bounce during transfer, and pieces may become trapped in the seal. A mistimed discharge can also split a dose between two packaging cycles. The weigher can report a good combination while the sealed bag ends up light.

When upstream and downstream readings do not agree, increasing the target should not be the first adjustment. Check product transfer, discharge timing, scale zero, checkweigher setup, and packaging tare before adding more candy to every bag.

How NIST Handbook 133 Checks a Candy Lot

The current NIST Handbook 133 edition is the 2026 edition. It provides procedures for checking packaged goods at the point of pack and in distribution.

Bagged candy generally falls under the Category A sampling plan. An official defines an inspection lot from the packages available for testing and then selects a random sample.

Under the standard Category A plan:

Inspection Lot Size	Random Sample Size	Packages Allowed Beyond MAV
1–11	Test all	0
12–250	12	0
251–3,200	24	0
More than 3,200	48	1

Handbook 133 evaluates the finished inspection lot. It does not certify a multihead weigher, bagger, or checkweigher. Equipment displays are not substitutes for the prescribed package test. State and local adoption should also be confirmed for the markets where the candy will be sold.

The Lot Average and the MAV Are Two Separate Checks

A lot is evaluated against two separate requirements.

The average requirement addresses systematic underfilling. In general, the actual lot average must at least equal the declared quantity. Category A procedures use the sample mean, standard deviation, and a Sample Error Limit when the sample average error is negative. A slightly negative sample average is therefore not automatically a failed lot.

The individual package requirement addresses unreasonably large shortages. Handbook 133 calls the threshold the Maximum Allowable Variation, or MAV. Its value depends on the labeled quantity and the applicable table. The sampling plan limits how many packages may have a minus error greater than the MAV.

The MAV is not:

• A recommended filling tolerance
• A symmetric plus-or-minus machine accuracy
• Permission to operate below the labeled weight
• A universal checkweigher reject setting

A large overfill in one bag does not erase an unreasonable minus error in another. The average requirement and the MAV limit must be evaluated separately.

Why Tare Weight Needs to Be Verified

For a packaged product, net weight is the gross weight minus the packaging tare. Handbook 133 testing therefore works with a nominal gross weight:

Nominal gross weight = Declared net weight + Average tare weight

Film, labels, zippers, closures, and other packaging materials contribute to tare. For individually wrapped candy, the inner wrappers are also part of the packaging weight. Changes in film gauge, bag length, label stock, or zipper construction can shift the average tare.

For ordinary candy, the Handbook 133 gravimetric procedure generally uses used dry tare taken from opened, emptied, cleaned, and appropriately dried packages. It is not always enough to weigh one unused pouch and enter that value into every recipe.

If the checkweigher monitors gross package weight against a nominal gross target, an outdated tare value can create false rejects or allow light net-content packages to pass.

How Far Above the Label Weight Should the Target Be?

In practice, the multihead weigher target normally needs to be above the labeled quantity. However, Handbook 133 does not prescribe one universal amount to add.

A working target can be expressed as:

Operating target = Labeled net weight + Data-based process allowance

The required allowance depends on the line’s actual performance. Collect finished-package data during stable production, startup, hopper refill, restart, and film changes. Record:

• Average finished-package weight
• Standard deviation
• Minimum and maximum weights
• Packages below the declared quantity
• Packages beyond the applicable MAV
• Checkweigher reject rate
• Average product giveaway

Compare the multihead weigher, checkweigher, and verified bench-scale results to identify any offset between them.

If the weight distribution is too wide, work on the cause before raising the target. Uneven feeder levels, sticky contact surfaces, unstable load-cell readings, poor discharge timing, product caught in the seal, and an incorrect tare recipe are common places to check.

Raising the target treats the symptom. Reducing variation fixes the process and allows the operating target to move closer to the label without increasing shortage risk.

What Each Scale Does on the Packaging Line

The weighing devices on the line should work together without being treated as interchangeable.

Control Point	Main Job	What It Does Not Prove
Multihead weigher	Control the product dose and reduce filling variation	Finished-package net content or lot compliance
Checkweigher	Monitor sealed packages, reject exceptions, and identify drift	Formal acceptance of an inspection lot
QA bench scale	Verify random packages, tare, and net-content trends	A valid result without proper sampling procedures

A checkweigher provides valuable 100 percent production monitoring. It can detect empty bags, missed discharges, double fills, and gradual process drift. Some systems can also provide feedback to the upstream filler.

However, online checking does not automatically replace the random sampling, tare determination, and statistical calculations used in an official Handbook 133 test.

What to Test Before Full Production Starts

A factory acceptance test should use the actual candy, target weight, packaging film, and planned production speed whenever possible. A short run under ideal conditions says little about what will happen during a full shift.

Testing should include:

• Startup and steady production
• Hopper refilling and low product levels
• Stop-and-restart cycles
• Film splices
• Recipe and target-weight changes
• Different candy batches
• Enough running time for sticky residue or crumbs to accumulate

Record sustained bags per minute together with the weight data. If the weigher average looks correct but the checkweigher reads light, investigate product transfer, tare, and checkweigher zero. If the average is acceptable but underweight rejects remain high, the process variation is likely too wide.

A FAT can evaluate the line using Handbook 133 concepts, but it should not be presented as an official government compliance inspection.

What Weight Data Should Be Recorded

For each SKU, retain the label quantity, candy and film specification, average tare, recipe version, production lot, random sample results, checkweigher rejects, scale verification records, and corrective actions.

When a package carries both U.S. customary and metric declarations, verify that the converted quantities are consistent. Federal food labeling requirements also apply through 21 CFR §101.7.

Good records help QA separate filler problems from tare, transfer, or measurement problems. They also support target adjustments based on actual data instead of an arbitrary safety cushion.

Reducing Underweight Risk Without Adding Too Much Giveaway

Reliable candy bag net weight control comes from a stable product dose, clean transfer into the bag, correct tare data, finished-package monitoring, and a documented sampling program.

The multihead weigher controls the dose. The checkweigher monitors the packaged output. QA verifies the inspection lot using the applicable procedure. None of these functions should be expected to do the job of the other two.

Send Smart Weigh your candy samples, labeled net weight, bag specification, current weight data, and target speed. Smart Weigh can test the actual weight distribution and recommend a weighing and inspection setup that controls shortage risk without building unnecessary giveaway into every bag.