Pressure relief valve (food packaging)

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Aroma protection valve on the inside of the coffee packaging

A pressure relief valve is used in the area of food packaging to allow the gases released by the food to escape in a controlled manner and at the same time to prevent air from entering the packaging. This prevents the packaging from inflating or even bursting and protects the quality of the packaged goods. Typical areas of application are, for example, the packaging of roasted coffee , fresh yeast dough or sauerkraut .

history

The first patent for the small plastic valve was filed in 1993 by the Italian Luigi Goglio. The design corresponds to the shape that is still often found today. In the patent EP0659657B1 (degassing valve for aromatic products such as coffee and comparable products), however, an additional upstream filter is described as an option, which is intended to allow only small molecules through, while retaining complex aroma molecules.

Despite the advantages for gas-generating foodstuffs, such valves could not gain acceptance for a long time, since the thermal sealing of the valves significantly extended the cycle times of the packaging machines. Only by welding the valves in by ultrasound could the valves be applied without extending the cycle times, as the process only takes a few milliseconds and there is no cooling time for thermal sealing.

Areas of application

Aroma protection valve of a coffee package (outside)

Coffee packaging

Freshly roasted coffee beans release larger amounts of carbon dioxide (CO 2 ) even after days . This can be up to six liters of gas per kilogram of coffee. It would be possible to let the coffee beans outgas for a longer period of time before packing, but flavoring substances would also be lost in the process. By using an overpressure valve in the packaging, the freshly roasted beans can be filled and packaged, with the carbon dioxide escaping from the packaging even at a very low overpressure of a few millibars without the packaging deforming. When the overpressure is released, the valve closes automatically. A penetration of oxygen and thus the Verranzen the aroma-bearing oils is prevented. Because of this protective function, the valves are also referred to as aroma protection valves or aroma valves for short.

In the case of coffee packaging, an internal valve is usually used, which is only visible from the outside through the imprint of the seal ring for fastening the valve and through one or more small holes in the film. Usually the valve is attached to the front of the product in the upper area. The constant outgassing of the coffee causes gas to flow out of the packaging together with some aroma molecules, which spreads a light coffee smell in the vicinity of the coffee department, which can be an incentive for customers to buy. The internal pressure is also slightly increased when the coffee packet is removed from the shelf and the coffee aroma escapes.

A cheaper alternative for the valve would be a simple hole. This, too, would lead off the resulting gases to the outside and prevent the packaging from inflating. However, oxygen penetrates the packaging through a simple hole so that the aroma would not be protected. Nevertheless, this variant is used.

Packaging of other outgassing foods

Fresh yeast dough contains yeasts which, when fermented, give off carbon dioxide even at lower temperatures. Ready-to-eat pizza dough is hermetically sealed in foil, which would inflate without a degassing valve and give the customer the false impression of spoilage. At the same time, the valve also prevents the ingress of atmospheric oxygen in this application if a negative pressure occurs as the temperature drops.

Even with fresh sauerkraut, fermentation takes place without thermal treatment. But there is also gas development in soy products , cheese or some pet foods.

Steam cooking in the microwave

Special one-way pressure relief valves enable food to be steam-cooked directly in the packaging in the microwave. While the valve is tightly closed during transport and storage and thus protects the product, the overpressure in the packaging that is necessary for steaming is created in the microwave by the formation of water vapor. The pressure is regulated by the valve, which opens when the pressure is too high.

Designs

Aroma protection valve (cross section), two-part housing (yellow) and sealing washer (gray) on the inside of a film (blue)

The pressure relief valve is one of the packaging aids that are applied shortly before or during packaging. There are internal and external valves for the designs.

Internal valve

Aroma protection valve (disassembled)

The internal valve consists of a two-part housing (valve body) and a flexible sealing washer in between. An elevation on the inner valve body presses the sealing disk downwards in the idle state, so that it rests flat on the lower housing part and the valve is closed. If the internal pressure increases, gas flows through the openings in the lower part of the housing and pushes the sealing washer upwards. Gas is released to the outside through the hole in the inner valve body and the holes in the packaging film. Typical response pressures of aroma protection valves are in the range of a few millibars . In order to guarantee the gas tightness of the valve, there is often a sealing oil on the sealing disc.

The valve housing has a typical diameter of 22-23 mm and a height of less than 4 mm. If the valve is used for products with a small particle size (e.g. powder coffee), there is usually a filter fleece in front of the openings , which prevents the particles from penetrating the valve and thus preventing malfunction.

Polyethylene is usually used as the housing material; the valve housings are occasionally made of polypropylene . The valve is welded to the foil either thermally or by ultrasound . With the latter method, higher clock frequencies can be achieved. The inside valve can only be recognized from the outside through the sealing edge and a few small holes in the foil. It is therefore inconspicuous and does not disturb the design of the packaging.

External valve

The variant on the outside is applied self-adhesive to the outside of the packaging material, but in principle has comparable properties.

Individual evidence

  1. ↑ a b Stefanie Krauß: It's a matter of taste: valve technology for the best product protection . Ed .: Bosch Packaging Technology. November 12, 2012 ( boschpackaging.com [accessed September 17, 2018]).
  2. ↑ a b Small valve with a big effect. wipf AG, accessed on September 15, 2018 .
  3. ↑ a b c What is the function of the valve in coffee packs? In: The coffee side - everything about coffee. Tim Kröner Internet Services, accessed on August 10, 2018 .
  4. ↑ Luigi Goglio: Degassing valve for aromatic products, such as coffee and similar products. (pdf) In: Patent EP 0 659 657 B1. June 21, 1994, accessed September 18, 2018 .
  5. ↑ valve applicator. Valves vent packaging. Kunststoffe.de, January 23, 2004, accessed on September 19, 2018 .
  6. ↑ What is the function of the valve in coffee packs? Kaffee.de, June 9, 2015, accessed on September 18, 2018 .
  7. ↑ Pizza packaging with pressure relief valve . In: bread and baked goods . tape 5 . f2m food multimedia gmbh, Hamburg 2006, p. 70–71 ( brotundbackwaren.de [PDF]).
  8. ↑ a b WICOVALVE for thermal sealing. Wipf AG, accessed on September 19, 2018 .
  9. ↑ a b Internal valve VIS / VAP. In: Bosch Packaging Technology. Retrieved September 19, 2018 .