Glass packaging material for foods and beverages

Glass packaging material for foods and beverages

Advantages and disadvantages of using glass as a packaging material for foods and beverages 
with reference to a high sales volume drinks bottle and a jar for jam (comfiture).

Quality defects that might be encountered with using glass containers and how these could be minimized
by the glass Manufacturer and Quality  tests  to be carried out by the glass Manufacturer to eliminate them.

 Gaetano Dagostino, CSQA Qualified BRC IOP  International Inspector
1.0 - Introduction
In this paper glass bottles for wine (both normal and sparkling) and jars for jam and comfiture will be considered.

1.1 - Wine
I would like to report some basic information of the products under consideration which will be helpful to understand the further technical considerations.

Wine is defined by Oxford dictionary as “an alcoholic drink made from fermented grape juice…”.
EC Reg. (CE) 1234/2007), defines wine as “the product obtained by a total or partial alcoholic fermentation of fresh grapes…". According to Italian Legislative Decree #109 (dated 27.01.2014), wine shall have alcohol content higher than 8.5% and up to 18.5%.
For the purpose of this paper, “wine” will include:
  • Non-sparkling red, white and rose’ wines, both “table” (or “normal”) wines and “quality wines”
  • Controlled Origin Denomination or Geographic Indication Protected or Typical)
  • Sparkling wines: Champaign and Italian Spumante
Narrow mouth bottles are used for wine.

1.2 - Jam and comfiture
Jam and comfiture, although commonly used synonyms, are two different types of food.
Jam is a food product obtained by boiling the fruit pulp with added sugar. From the point of view of Italian legislation (Decree of 20 February 2004 no. 50), jams (in Italian “marmellata’ ) is a product prepared from the pulp and / or purée of one or more fruits and shall have not less than 35% of pulp fruit; “extra” jams shall have a minimum of fruit pulp of no less than 45%.
Comfiture (in Italian ‘Confettura)” is a product prepared only by boiling the pulp, puree, juice, aqueous extracts and peel of citrus fruits. Minimum fruit content has to be 20%, of which at least 7.5% must come from the fruit endocarp (which is the edible portion of citrus fruit).

After boiling, both jam and comfiture are hot filled at a temperature ≥ 80°Cand pasteurized (normally for 1’ at 90°C). There is only one type of jam, called “freezer jam”, which is not pasteurized, but this is a homemade product not for sale.
Sugar is added to jams and comfitures with the dual purpose of improving the organoleptic characteristics and increasing product lifetime (because it reduces the availability of water, an essential element for the degenerative processes of the food).
Large mouth bottles are used for jam and comfiture.

2.0 – Advantages of using glass as a packaging material for foods and beverages
2.1 – Advantages
  • Impermeability -  Glass is impermeable to gases and moisture vapor. This property is important for all food and beverages and in particular wine and jam/comfiture. For wine, impermeability protects the wine from being contaminated by the odors of the ambient and from losing the organoleptic properties which is important for the long term storage of quality wines (mainly red). For Champaign and sparkling wines, impermeability ensures durability of the “perlage” (“sparkle” or “effervescence” in English). Internal pressure of sparkling wines ranges from 3 to 6 bars.
  • Visibility -  the consumer can immediately see the color of the product before buying it. Normally bottles for red wines are dark to protect wine from light, mainly ultraviolet component of sunlight which is responsible of the oxidation of colored components of red wines.
White and rose’ wines use either transparent or light dark bottles because of lower colored components content. For jam, transparent containers are used, since the effect of light is not a big issue.
  • Rigidity - this ensures the shape ad volume stability of the product both under vacuum (e.g., jams) or under pressure (e.g., sparkling wines). Rigidity implies also that wine bottles and jam jars are not deformed during transportation handling and volume declared on the label is reliable.
  • Inviolability - glass cannot be perforated by syringes and this is a big advantage to avoid and prevent product boycotting and bio-terroristic attacks. This is nowadays a more and more important issue for the food Companies. The evidence of the increasing importance of food safety in food packaging is the recent issue of PAS 223 which emphasizes the prerequisites required to prevent boycott and bioterrorism and to increase bio-vigilance.
  • Resistance to thermal shocks: this is important for those food and beverages requiring pasteurization, jam hot filling (normally at 80 C) and jam pasteurization (normally 1’ at 90 C)

2.2 – Disadvantages of using glass as a packaging material for foods and beverages.
The most common disadvantages reported in the literature are:
  • Weight: a bottle of sparkling wine can weigh up to 750 grams (which is roughly equal to the weight of the product !). A PET bottle, on the contrary, can weigh less than one tenth (75 grams). In addition to that, PET bottles can be transported as a pre-form having a much lower volume of the final content.
  • Breakability: this has an adverse effect on both operators health during manufacturing and handling operations and, much more important, on the final consumer, in case of glass fragments inside bottle coming either from a manufacturing defect or from broken edge during filling.
  • High transportation cost as compared to the cost of product: unfortunately glass bottles cannot be produced by…glass preforms as PET bottles can! A truck transporting 10,000 glass bottles of 750 ml each, transports a volume of air equal to 10,000 x 750 = 7,500,000 ml = 7.550 liters of air (7.5 m3 of… air !).
  • Noise generated during filling operations: this issue is nowadays achieving an increasing importance, mainly in Europe and US, where laws establish limits for the noise in production departments and unions are very sensitive to this issue!
  • Water footprint, i.e., the quantity of water needed to produce a bottle of glass. High demand of water needed in production process, mainly for cooling. This is a restriction factor for areas of low water availability. “Water footprint” is having an increasing importance in those countries of environmental friendly culture.
  • To produce one kg of PET 17.5 kg of water are needed ( now with one kg of PET around 25 bottles of 200 ml can be produced. Consequently, roughly 0.7 l of water is needed to produce a 200 ml PET bottle, while to produce a glass bottle of 200 ml about 230 liters of water are needed (
  • Sodium and other ions could migrate in some conditions from glass to the food.
  • CO2 footprint: CO2 is developed during glass production both from the combustion of fuel and from the decomposition of limestone and dolomite utilized as raw materials. According to Pilkinton ( to produce 1 kg of glass, 1.1kg of CO₂ is produced.
    On the contrary, according to (, to manufacture 1 ton of PET around 3 tons of CO2 are produced. According to this data:
  • to produce 1 ton of glass, 3.3 tons of CO2 are produced.
  • to produce 1 ton of PET, 3 tons of CO2 are produced.
Consequently, the CO2 footprint is not an issue against glass, as it is commonly rated.
  • Energy consumption: high energy is required by the glass production process which hardly compensates the low cost of raw materials utilized, easily available all around the world.
The following is a simple comparison between glass and PET, as far as energy consumption is concerned.
The energy necessary to produce 1 Kg of PET is equal to 100 MJ. If we consider that 1 ton of oil is equivalent to 42x103 MJ, then we can roughly say that to produce 1 ton of PET, 2 tons of oil are needed (personal calculation, based on data from and

To calculate the amount of energy needed to produce 1 ton of glass, in absence of reliable scientific data, I have made following reasoning: the literature reports that 2.55% of energy required to produce 1 ton of glass is equal to 130 l of oil. Consequently, if we indicate with x the amount of oil needed to produce 1 ton of glass, following equation will be valid:
2.55:130 l of oil = 100: x
x= (130 l of oil x 100) : 2.55 = 13.000 :2.55 = 33,150 l of oil = 33 tons of oil (rounded)
Consequently, to produce 1 ton of glass 33 TEP are needed, which is roughly 15 times more than the energy required to produce 1 ton of PET.

3.0 – Balance between advantages and disadvantages
Jams and comfitures: they are filled only in glass containers because both products are hot filled and pasteurized and no plastics containers, even laminated with an aluminum interlayer, would stand the temperatures of these two processes and migration could occur from plastic to the food. Metal containers would work, but they would be more expensive and heavier.
Wine – As of today, only a few percentage of wine (around 10%) is sold in containers other than glass. The two “rivals” of glass are the BIB (Bag-In-Box) which consist of a strong plastic bladder (or plastic bag), usually made of several layers of metalized film or other plastics, seated inside a corrugated fiberboard box) and metal ( in USA only). Apart from the described advantages, an overriding factor in favor of glass bottles for wine is the general belief, mainly in the historical wine producing countries like Italy, France, Spain, etc., that buying and drinking wine (especially quality wines), in containers other than glass is a clear negative status symbol for both the Consumer and the… wine.

4 0 - Quality defects in glass containers for wine and jam
Quality defects can be categorized per type, area of the container where they usually occur and gravity on consumers’ health:
  1. Type of defects:
    • Cracks
    • Splits
    • Checks
    • Seams
    • Non-glass inclusions
    • Dirt
    • Spikes, bird cages, glass filaments
    • Freaks
    • Marks
  2. Area of the bottle where they occur
    • sealing surface and finish area: off-set finish, bulged finish, broken finish, corkage check, neck ring seam, dirty or rough finish, bent or crooked finish
    • neck: seam on necking parting line, bent neck, long neck, dirty neck, punched neck, tear on neck
    • shoulder: checks, thin shoulders, sunken shoulders
    • body: stringy glass appearance, blank and blow mold seam, bird cage, checks, sunken sides, bulged sides, washboards.
    • heel and base: flanged, thin, thick, heavy, rocker bottom, slug bottom, baffle marks, heel tap, slug bottom, swung baffle.
  3. Gravity of their consequences on people
    • Critical defects: defects which can cause serious physical damage to the final consumer of the product or when containers are handled.
    • Major (or Primary or Functional) defects): defects which prevent the container from being used or which could cause a deterioration of the product due to an inefficient closure system.
    • Minor (or Aesthetic) defects: defects of only aesthetic nature which do not affect functionality of container or do not constitute a hazard for the consumer or when containers are handled.
The following Table A reports types and a short description of the main defects and possible corrective actions aiming to eliminate these defects during production:


Critical defects Description Corrective actions
  1. Unstuck or stuck pieces of glass inside bottle
Glass pieces (smaller or bigger than bore size) free or stuck inside container.
This is the most critical defects
  • Decrease glass or plunger temperature
  • Tighten the plunger adaptor to the rod of piston
  • Increase the exhaust hole size
  • Change the plunger
  • Optimize cooling air flow to plunger
  1. Glass spikes inside
A thorn of glass in the body or in the bottom of container
  • Remove glass remains in flow head
  • Reduce plunger time inlet
  • Change shears
  • Decrease the speed of the machine
  • Slightly delay the vacuum inlet
  • Remove glass particles when mold is changed
  1.  Bird cage/bird swings
A filament or a surface of glass connecting two sides of container Same as 2)
  1. Finish defects (split, checks, broken, chipped, off set, bulged, unfilled, crooked, overpress susceptible of breakage, tear)
Cuts, checks, incomplete filling, excessive material, tear initiations, etc., in the finish area
  • Adjust gob temperature
  • Shorten plunger contact time
  • Change neck ring
  • Dehumidify blow air
  • Optimize mold closing time/speed
  • Increase gob weight or modify shape
  1. Filaments
A hair like string of glass inside bottle Same as 2)
  1. Cracks
Small fractures mainly in heel area
  • Increase glass temperature
  • Increase machine speed
  • Stabilize Leher temperature
  1. Freaks
Completely distorted shape which make the container completely unusable
  • Correct set up parameters
  1. Uneven glass distribution affecting strength
Thin spot in the bottle well below the acceptable thickness
  • Decrease glass temperature
  • Eliminate glass temperature differences
  • Decrease the gob shape
  • Load correctly the gob
  • Increase hardness of parison
  1. Internal dirt
Foreign materials in the bottle, normally introduced during warehousing or transportation, e.g., dust, dirt, cobwebs, spiders, flies, mosquitoes, small butterflies, interlayers crumbs, etc.
  • Introduce GMP in warehousing, packaging and transport
  1. Blisters
Thin skin deep blisters near or on external surface
  • Dehumidify blow air
  1. – Main major defects
1)- Dimensions out of tolerances
2) Capacity out of tolerance
  1. Out of round or off gauge bore size
  2. Out of shape bottle
Reduce glass temperature, reduce the hot ring temperature, reduce machine speed, clean the neck ring, verify air blow pressure, change the blow mold.
If uneven or bad distribution of glass is causing off spec capacity: correct glass temperature, verify any temperature gradient in the gob, verify cooling speed rate of blank molds
3 ) Seams on top or on the side of finish Visible junction line of the two half mold Adjust feeder temperature, change neck ring, reduce pressing pressure
4) Washboards A wavy condition of horizontal lines in the body of the bottle Eliminate any temperature gradient in the gob, correct shape of gob, verify setting of drop guide, verify blank design
5) Skin blisters on the body Small bubbles in the body glass Increase the level of glass in the furnace, increase the temperature on the feeder plunge, decrease the temperature of blanks and plungers
6) Small inclusion of non glass material Small pieces of refractory or not melted batch materials Causes: pieces of refractory material of the furnace falling into molten glass. Contaminated batch materials. Contaminated cullet. Flame impinging on furnace refractories.
7) Rocker bottom A sunken centre portion at the base of the bottle which makes bottle unstable when placed on a flat surface  Reduce glass temperature, reduce takeout time, increase cooling time
8) Flanged bottom A rim of glass around the bottom at the parting line Adjust feeder temperature, correct bottom plate height, check blank/baffle matching
9) Orange peel appearance of external surface Orange peel-like external surface Correct the shear cut, change plunger and neck ring, reduce the oil spray, improve polishing of mold and neck ring
10)- Dirty on external surface Carbonized crumbs of foreign material on external surface Reduce oil spray on shears, clean blank and/or blow mold, reduce sulphur content in the cullet

Minor defects can be considered: washboard, external dirt, impact mark, prominent mold joint, hard air bubbles (deeply embedded in the glass body), neck ring seam, wavy internal surface, small bubbles (seeds)
  1. – Quality tests mandatory for glass bottles
    1. - Quality tests to be performed on-line on 100% of the bottles
      • Bottle spacer: creates a space between the bottles on the conveyor belt to avoid contact
      • Squeeze test: each bottle is squeezed between two discs to measure cross breaking resistance
      • Bore gauger: measures the bore gauge against agreed or established specifications and Tolerances
      • Checks detection: a beam of light focuses onto pre-established bottle areas where these defects are statistically located
      • Wall thickness: wall thickness measurement by using dielectric properties of glass
      • Visual check: bottles are visually inspected by an operator
      • Automatic hot end inspections should be carried out before annealing with more advanced techniques like optical devices to detect, blisters, checks, cuts, bird swings and other irregularities by rotating bottles
All faulty bottles are scrapped and crushed into cullet.
  1. – Quality tests to be performed in the lab on statistically basis
    • Capacity, ovality, verticality
    • Vertical load resistance: measures resistance of bottles during capping or through stacking products on top of each other
    • Impact test: resistance to impact, measured generally with Pendulum Impact Tester
    • Thermal shock resistance: to determine resistance to thermal shocks of hot fill or pasteurized products (e.g., jam). Testing methods: ASTM C149 or BS EN ISO 7459 at 420 ⁰C
    • Coating performance: to determine longevity of of the coating performance - Internal pressure resistance: for bottles containing sparkling wines - Residual strain measurement: measures the annealing stress/residual strain – Testing method: ASTM C 148
    • Hydraulic internal pressure: according to ISO 7458
Sampling procedures and schemes inspections by attributes are indexed by Acceptance Quality Limits (AQL), according to UNI ISO 2859/3 or to Military Standard 105 E.

CSQA Qualified BRC IOP  International Inspector for Paper and Cardboard, Wood, Plastic, Glass and Metal Packaging.
REFERENCES AND BIBLIOGRAPHY (Apart from the references reported in the text)
  • Glass containers defect – Causes and remedies – Copyright EMHART GLASS – TW0738/1191 (no date)
  • Packaging Technology – Chapter 8 – Glass containers
  • Glass in packaging - C.S. Purushothaman – CSP – TRG – AIDS – August 2008 – 1 – Power point presentation
  • Bruni Glass defects on bottles – available in
The Science of Quality – Italian monthly magazine – Special issue for jam and comfiture – March 2009