How do you inspect the quality of glass wine bottles?

When bottle quality slips, leaks and breakage hit the winery, not the glass plant. A tight inspection plan keeps corks sealing, screwcaps torquing, and pallets arriving intact.

Inspect wine bottles with a layered system: 100% critical defect vision, finish and capacity measurements, stress checks, and strength tests. The focus is closure fit, base stability, and durability through filling, shipping, and storage.

What does a complete wine-bottle QC plan look like?

Start with “fit, fill, survive”

A wine bottle is a packaging part, not a decoration. So the inspection plan should match how the bottle fails in real life. Most problems fall into four buckets: closure failure, instability on the line, cosmetic damage that becomes breakage later, and strength failures in transport.

A practical plan uses two layers of control. The first layer is process control at the glass plant: cavity traceability, stable gob weight, stable mold temperatures, and stable coatings. The second layer is product verification: measurements and tests on finished bottles that prove the lot can run on a corker or a Stelvin capper without surprises.

Classify defects so everyone speaks the same language

The fastest way to stop arguments is to define defect severity and the action for each class using Acceptance Quality Limit (AQL) sampling rules ¹.

Defect class	Examples	Risk to winery	Inspection style	Typical rule
Critical	cracks, open checks, stones, major blisters, bird swing, broken finish	leak, breakage, safety	100% vision + reject	AQL = 0
Major	heavy seams, bad finish geometry, base wobble, deep scuffs	line stoppage, high rejects	high sampling + containment	very low AQL
Minor	light scuffs, small bubbles not near surface, slight cosmetic haze	appearance complaints	sampling	agreed AQL

Use traceability to turn defects into fixes

Base codes and cavity numbers should be readable and recorded. When one cavity drifts, fast isolation saves the lot. A winery does not want 10,000 bottles quarantined because one cavity had a worn neck ring.

A short story from the field still sticks in my mind. One customer had “random” cap leaks. The leak rate vanished when bottles from one cavity were removed. The root cause was a small finish ovality drift after a mold repair. That problem only became visible because the inspection report tracked defects by cavity.

Now the deeper questions matter, because closure fit, visual defects, strength testing, and grading rules are the four places buyers win or lose.

If these four areas are locked, mass production becomes calm.

Which dimensions ensure cork and Stelvin sealing and torque?

Leaks feel like a closure problem, but the bottle finish is often the real cause. One millimeter of drift can destroy a cork seal or a screwcap thread.

The key dimensions are finish inner bore, seal land, thread geometry, and roundness. Verify them by gauge and by torque or pull tests on real closures, not only calipers.

For cork: bore, top surface, and insertion geometry

Cork sealing depends on controlled compression and a clean, round mouth. A standard still-wine cork is often around 24 mm diameter (#9 cork). The bottle mouth inner diameter is smaller, often around 18–19 mm at the bore, so the cork compresses and seals. That only works when the bore is round and smooth.

What matters most:

• Bore diameter and roundness (too large or oval = weak seal)
• Top surface flatness (chips or waviness = leak path)
• Mouth finish chips and checks (crack starters during corking)
• Neck alignment (tilt can scrape cork and create channels)

For Stelvin/BVS screwcaps: thread, seal diameter, and support ring

For BVS 30×60 systems, the bottle finish is not “generic.” It is a defined geometry. Typical BVS 30×60 specs include items like thread diameter, seal diameter, and locking ring diameter, each with tight tolerances (for example, thread diameter around 28.3 mm ± 0.3 and seal diameter around 26.1 mm ± 0.3 on common BVS 30×60 guides). The exact numbers should match the agreed finish sheet for the bottle—use a BVS 30×60 finish specification guide ² as the shared reference.

What matters most:

• Seal diameter and rim quality (liner needs even compression)
• Thread start and thread form (prevents cross-thread and slip)
• Locking ring geometry (controls tamper band behavior)
• Finish ovality (drives torque scatter)

Turn dimensions into acceptance criteria buyers can enforce

Do not stop at “in spec.” Connect dimensions to closure performance.

Closure system	Dimension to control	Why it matters	Quick functional proof
Cork	bore ID + roundness	controls cork compression	leak test after corking + vacuum/pressure hold
Cork	mouth chips/checks	creates leak and crack origin	100% finish vision + chip gauge
Stelvin/BVS	seal diameter + rim flatness	liner seal needs uniform land	torque + leak test after capping
Stelvin/BVS	thread diameter + lead	controls application torque and slip	slip/break torque window on real caps
Both	finish tilt/ovality	drives sealing scatter	go/no-go gauges + closure trial run

A purchase spec should name the finish standard (like BVS 30×60 or the agreed cork finish), set measurement methods, and require a short closure trial before full shipment approval.

What visual checks catch seams, checks, and base wobble?

Most defects are visible early if the inspection view is correct. The mistake is checking only “pretty” surfaces and ignoring finish and base details.

Use targeted visual checks: finish and thread, sidewall seams, shoulder and heel checks, and base flatness. Combine high-speed vision with simple manual confirmations like a wobble test and light-line inspection.

Where to look first: finish, heel, and seam line

For wine bottles, the most expensive rejects happen at the winery, not at the glass plant. So visual checks should follow failure risk:
1) Finish and sealing land (chips, checks, dirty rim, malformed thread)
2) Heel and base edge (impact sensitive, crack starts here)
3) Side seam and mold parting line (sharp seams can cut labels and start scratches)
4) Shoulder transitions (thin zones and stress zones)

A good inspection station uses controlled lighting:

• bright-field to see bubbles and stones
• dark-field to highlight surface scratches and checks
• finish cameras angled to catch thread damage
• base cameras for stones, thin heel, and rocker base

Base wobble: simple test, high value

Base wobble looks minor until it jams a conveyor or makes a labeler misplace. Wobble also hints at uneven glass distribution in the heel.

Fast checks that work:

• Rocker test on a flat plate (manual or automated)
• Base ring thickness sampling by cavity
• Punt symmetry check for premium bottles

Make visual inspection actionable with defect maps

The fastest improvement comes when defects are coded by location and cavity.

Visual defect	What it often means	Where it shows	Fast containment
sharp seam	worn mold or misalignment	vertical line on body	isolate cavity, repair mold edge
vertical check	mold too cold or drafts, stress	shoulder/heel	adjust cooling, verify annealing
bird swing	unstable gob/shear	random glass string	stop and correct shear timing
stones/blisters	melt/refining issue	body or base	quarantine lot, raise refining control
base wobble	uneven heel distribution	base edge	adjust bottom plate cooling and timing
finish chip/check	handling or neck ring wear	rim/threads	100% finish sort, fix transfer points

For buyers, the key is to require finish and base inspection data, not only “body cosmetics.” Those are the two zones that decide sealing and durability.

Which drop and pressure tests validate logistics durability?

A bottle can pass visual inspection and still fail in shipping. Logistics failure is a mix of bottle strength, packaging design, and handling shocks.

Use a test ladder: vertical top load for stacking, internal pressure for sparkling safety, and packaged drop/vibration to validate pallets. The goal is performance with real cartons and dividers, not only bare-bottle tests.

Vertical load: prove stacking and pallet strength

Top load testing checks how the bottle survives stacking forces in pallets and cases. This is critical for heavy bottles and for export routes with long storage.

What to do:

• test bottles from multiple cavities
• include wet conditions if your line sprays water
• set pass limits based on your pallet pattern and layer count

Internal pressure: essential for sparkling and safety margins

Still wine has low internal pressure, but sparkling wine bottles must hold pressure safely. Internal pressure tests aligned to ISO 7458 internal pressure resistance methods ³ prove that the glass distribution and defect control are strong enough.

What to do:

• define pressure ramp method and hold time
• test after thermal conditioning if bottles see warm warehouses
• confirm failure mode (base vs body vs finish) to guide improvements

Packaged drop and vibration: validate the real system

Most breakage happens as a packaging event, not as a bare bottle event. So drop and vibration tests should use:

• real cartons or trays
• real dividers
• real pallet wrap pattern
• real bottle coatings (COF matters for rub damage)

Test	What it proves	When it matters most	Buyer-friendly acceptance idea
Top load (axial compression)	stacking strength	pallets, warehousing	minimum load with safety factor
Internal pressure	safety for sparkling	sparkling lines	pass at target pressure + low scatter
Drop (packaged)	shock survival	courier, export, rough routes	no break at defined drop heights
Vibration (packaged)	rub and fatigue	long truck/sea routes	low scuff and no breaks after run
Leak test (post-closure)	seal integrity	all lines	0 leaks in defined sample

If the buyer wants fewer surprises, the best move is to require one “pre-production validation lot” that runs these tests before the first big shipment.

How do color tolerance and glass weight affect grading?

Color and weight decide whether the bottle looks premium and whether it behaves like a premium bottle. They also decide cost, carbon footprint, and break risk.

*Control color with spectro or Lab targets, not only by eye. Control weight by cavity and by minimum strength needs. Grade bottles by how color and mass affect light protection, feel, and logistics cost.**

Color tolerance: protect wine and protect brand identity

For wine, color is not only style. It controls light exposure. Green and amber help reduce light strike risk. Flint is popular for rosé, but it needs better storage control. So grading should include both appearance and performance.

Practical color control steps:

• set a target color family (flint, antique green, dead leaf, amber)
• define tolerance with ΔE or transmission bands based on the CIE Lab* color space ⁴
• check lot-to-lot consistency, not only average

Glass weight: strength, feel, and shipping trade-offs

Heavy bottles feel premium. They also cost more to ship and can raise break risk in handling if the line is not tuned, because heavier bottles hit harder. Lightweight bottles save cost and carbon, but they need tighter thickness control and better coatings.

A buyer should treat weight as a controlled spec:

• average weight target
• weight tolerance band
• minimum local thickness at heel and shoulder
• cavity-to-cavity scatter limit

A grading model that buyers can use in contracts

Instead of “premium vs standard” by opinion, grade with measurable bands.

Grading factor	What to measure	Why it changes value	Simple pass rule
Color match	ΔE or transmission band	brand consistency and light protection	within agreed tolerance per lot
Color uniformity	streaks, cords visible	looks cheap and signals melt issues	no visible streaking beyond limit
Bottle weight	average + cavity scatter	affects shipping and perceived quality	within band, low cavity spread
Weight distribution	heel/shoulder thickness	affects breakage and top load	minimum thickness at critical zones
Clarity and defects	bubbles, stones, haze	affects premium look and safety	critical defects at AQL 0
Surface condition	scuffs, coating	affects label and break risk	COF stable and low scuff rate

The best contracts tie color and weight grading to end use. A winery that sells long-aged reds may accept heavier antique green. A fast-turn rosé brand may accept flint and lighter weight but will demand tighter visual and closure performance.

How do audit results and references confirm reliability?

Many buyers stop at price lists and samples. The real test is how the factory runs on a normal day when nobody is watching.

Use audits, trial runs, and customer references to test if a manufacturer keeps promises on quality, delivery, and problem-solving, not just in the first order but over years.

Factory audits: what you should see on the ground

If you can visit, even once, it gives you a clear picture.

Walk through:

• Batch house and raw material storage. Are materials dry, labeled, and tracked?
• Furnace and forehearth area. Is there clear control of temperature and color?
• Forming area. Are operators trained, with clear work instructions at each line?
• Annealing lehrs. Is there recorded temperature control and belt speed logs?
• Cold-end inspection. Do they use 100% automatic vision inspection ⁵ for critical defects like cracks, blisters, and stones?
• QC lab. Do you see real testing gear for top-load, burst, ΔT, and dimensional checks?

You do not need to be an engineer to spot big issues. Dirty floors, poor lighting, and random piles of pallets are strong early warning signs.

If a visit is not possible, ask for a remote audit with photos, videos, and document review. Many of our overseas clients start this way.

First-article approval and ongoing quality data

Before full production, insist on a first-article inspection (FAI) or PPAP-style package:

• Full dimensional report vs drawing.
• Top-load, burst, and thermal shock (ΔT) testing ⁶ results.
• Visual defect rate data with AQL levels.
• Polariscope strain inspection ⁷ pictures for strain.

For mass runs, ask what AQL they use for critical, major, and minor defects. If they can speak about capability in simple terms, it shows they watch trends, not only reject after the fact.

References and reliability history

Finally, ask for references from customers in a similar segment:

• For example, a craft spirits brand if you are launching a new whiskey.
• A cosmetic brand if you buy for skincare.
• A food brand if you pack sauces or honey.

Good questions for references:

• How often do you see quality issues, and how fast are they fixed?
• How is on-time delivery performance?
• How did the manufacturer handle the biggest problem you had together?

Also listen for what they do not say. If a reference hesitates, or refuses to talk about current volumes, there may be a reason.

From our side as a manufacturer, we always invite new clients to start with a smaller project, review the first run together, and only then scale up. That way both sides see how we work under real pressure.

Evidence type	What it tells you	Warning sign
Audit report	Process control and housekeeping level	Many open nonconformities, no deadlines
FAI / PPAP pack	Real performance vs drawing and specs	Only visual approval, no test data
Long-term customer	Stability and problem-solving over years	Only very new or very small references

Conclusion

Inspect wine bottles by proving closure fit, visual integrity, strength in load and pressure, and stable color and weight. A clear defect class system and cavity traceability make mass production reliable.

Footnotes