It is very important, for the good presentation of a preserves packed in glass jars, closed with “twist-off” type caps that are free of bumps and oxidations. To avoid the presence of the latter, the manufacturer of the covers should take all possible precautions to avoid damaging the exterior system, paying particular attention to the finishing varnish. But it is in the packaging operation that extreme measures have to be taken to reduce the chances of deterioration and corrosion of the varnish. Let’s see some factors that can affect the external oxidation of the caps:



Normally two types of hot treatment are applied to glass jars, based either on tin oxide or titanium oxide. In both cases it is good that the mouth finish of the jar is protected from contamination with these materials, being more critical caused by the tin, due to its conductivity. Thus, threads of a bottle contaminated with this treatment increase the risk of oxidation of the lids of the lids by electrolytic corrosion. Glass manufacturers already take this into account, not only because of the risk of oxidation of the lid but also because of the effect that such treatments can have on their opening pairs.



If the water in the boiler has been treated correctly to avoid corrosion, normally the steam condensation of the same will not be corrosive, being suitable for proper conditioning adequate values ​​of water alkalinity. The use of volatile alkalis, which are linked to steam, helps to neutralize the acidic effects of carbon dioxide in the condensed vapor.

An aggressive or polluting vapor can have its origin in: a) An inadequate way to operate the boiler (examples: try to produce more steam than the type of boiler admits, a high level of water in it that reduces steam space operate at lower pressures than the design pressure …), b) The chemical conditions of the water (examples: high concentrations of dissolved solids …)

The most common cause of water deterioration of a boiler is produced by not respecting the parameters of the process that the manufacturer recommends.



If pasteurizers, autoclaves, baskets or pipes have oxidations, they can cause oxide transfer to the lids during the process, increasing the possibility of corrosion of the lids. To avoid this, an appropriate treatment of the water used during pasteurization and cooling is required. When the water is recirculated, (in continuous pasteurizers and Rotomat type autoclaves) it is advisable to change the water at least once a week, or put a filter in the system, to remove accumulated rust particles that could be deposited on the covers.



The bottles can be processed in: a) To the “Maria bath” (open bath or continuous pasteurizer); b) Under pressure (closed bath with overpressure). In both cases during the heat treatment and cooling, the two necessary factors are present for oxidation to take place: humidity and air. It is therefore advisable to reduce as much as possible the other corrosive effects of the water used, for which the “inhibitors” are used.

The suppliers of water treatment agents offer a range of appropriate additives in each case. It is desirable to be advised by them to choose the most effective additive / inhibitor depending on the type of water and circulation system used.

The products used should not have an adverse effect on the external decoration of the caps, even at temperatures of up to 125 ° C and in the cooling water they should not reduce the disinfection or the bactericidal treatment used. Such additives can also serve as film-forming agents by spreading the water retained on the lid in the form of a thin layer, avoiding the permanence of drops which are difficult to remove and which dry very slowly.

Care must be taken that the cooling water does not contain excessive concentrations of chlorides or sulfates, which would facilitate corrosion. As a general criterion, chlorine levels of more than 10 ppm should not be exceeded.



It is advisable not to overcool the bottles after the process, thus facilitating the possibility of the lids and bottles drying out with the help of residual heat. The ideal temperature for this is of the order of 40º C. If it were greater it would help drying, but there could be an excessive appearance of spores of thermophilic micro-organisms that would have survived the process. On the contrary, excessive cooling of the bottles, apart from significantly reducing the efficiency of drying the lid, can also make labeling more difficult. If baskets are used, they should be tilted to allow drainage of excessive water remaining in the lids.



Improper drying of the lids before packing can cause oxidation during storage. Usually the residual heat contained in the jars is not enough to evaporate the water from the lid itself. To complete the operation, it is appropriate to use air dryers. The design and arrangement of the air jets in the drying units is very important in order to eliminate as much moisture in the skirt of the covers, especially in the nails of the Twist-off type. It is also convenient to keep the bottles for a time not less than 2 minutes in the transporters before their arrival at the packaging station.




Ideally, jars should be stored in a cool, dry place. For this, apart from avoiding rain and steam in this area, it is also necessary to avoid the condensation of atmospheric humidity in the covers, this condensation can happen as long as the temperature of the bottles is below the dew point of the ambient air . Such conditions are created when moist air has access to a relatively cool store. To avoid this, the doors should be left open only when the outside humidity is low. You can also install air conditioning, we recommend a temperature between 10 to 15 º C in the room.

As for the packaging material, it is advisable to specify paper or cardboard with a chloride content less than 0.05% and sulfates at 0.15%.



To minimize the possibility of external oxidation of the caps, attention should be paid to the following points:


1.- Manipulate the covers with care before, during and after the closing operation.

2.- Check that the bottles do not get too cold.

3.- Maintain pasteurizers, autoclaves and auxiliary equipment without oxidation.

4.- Incorporate the appropriate additives into the process water.

5.- Establish a procedure that ensures that the lids arrive dry when packed.

6.- Use in packaging, paper or cardboard low in chlorides and sulfates.

7.- Control humidity and temperature in the warehouses of finished product.

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