Shelf Life extension of food can be by a number of techniques. We explain and demystify how these processes work and give examples of applications they are suitable for.
Hot fill/Cook –Chill
Cook Chill is a very cost effective means of adding shelf life to food. The technique involves fully cooking the product, filling into a pouch (typically) at temperatures in excess of 85 Deg C followed by rapid chilling and storage at 0-4 Deg C. Common applications are bulk food manufacture for institutions such as hospitals and schools and soup and sauces in retail ready standup pouches.
This is a process that occurs after food is packed. The pack is then heated to a temperature in excess of 100 Deg C. Pasteurisation will normally achieve a longer shelf life than Hot fill. Depending on what constituents are in a soup or sauce mentioned above, often this additional thermal treatment is required for shelf life extension.
Retorting in flexible packaging is a food processing method normally using trays and pouches, where the food is packaged first, and then heated to temperatures typically in excess of 120 Deg C in a retort chamber to sterilize the product hence achieving a long shelf life at ambient temperatures which can be up to 1 year. Hence the barrier required for this process is the most demanding of all at < 1 cc/m2/24 hrs. Common applications are meat based casseroles, long life sweetcorn, Abalone.
Modified Atmospheric Packaging [MAP]/Gas Flush
Unlike the techniques that utilise thermal processes to extend shelf life, MAP changes the ambient atmosphere in the pack to stifle bug growth. Normal oxygen (O2) levels are around 21% so often we will try the reduce that level as low as possible and replace it with carbon dioxide (CO2) and perhaps an inert buffer such as Nitrogen (N2) to stop pack collapse once a large portion of the CO2 has been taken up in the product.
Red meat however discolours at low O2 levels so we then modify the atmosphere in the other direction and increase the O2 levels to say 80% once again curbing the rate of bug growth but preserving good colour in the meat.
There are many applications such as red meat, as mentioned, in rigid trays with a clear lidding film, bulk MAP of whole chickens and nitrogen displacement of O2 in snack food packs such as potato chips.
Probably the most economical means of extending shelf life. Again the idea is to reduce the oxygen (O2) levels to as low as possible via extreme vacuum. The pouch or thermoformed pack must have a good barrier to prevent O2 re-entering the pack. In some cases where say bone-in meat is being vacuum packed, a high puncture resistance pouch maybe be required.
As the name suggests, this packing process uses heat to form a flexible “pocket” or rigid tray out of a base material called Bottom Web. The product is loaded into these pockets or trays and then a film (top web) is heat sealed to the bottom web after vacuum to form a vacuum pack. Two common variations on this technique are using the thermoformer to make a rigid tray but substitute a top web for a lidding film and gas flushing the pack. The other variation is forming a shallow tray then using a skin to drape around the product before pulling full vacuum to create a skin pack. Thermoforming is widespread in the Meat, Dairy and Smallgoods industries.
Vertical Form Fill Seal [VFFS]
VFFS is effectively making a pack out of a roll of film. Normally the VFFS machine will have a weighing machine over it which dumps product down a shute. The film wraps around this shute and is normally fin sealed on the back to form a tube. As the tube drops down one repeat, jaws seal the bottom of the pack and seal and cut off the previous pack which drops onto a conveyor. Packing of snack foods such as nut and chips is a common application in conjuction with an oxygen purge MAP system to extend shelf life.
Horizontal Form Fill Seal [HFFS] /Flow Wrapping
HFFS or Flow wrapping works on a similar principle to VFFS except the formed tube runs horizontally through the Flow Wrapper. Once again, these products can be gas flushed as well. This technique is ideally suited to bulky items such as bakery products.
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Probably the earliest means of extending shelf life in food. The product is inserted into a vacuum pouch then placed in a Vacuum chamber with the mouth of the pouch resting over a sealing bar. The chamber is closed, a vacuum is pulled then the mouth of the bag is heat sealed to retain the vacuum. Not generally to any products that will crush easily, common applications are smallgoods, fresh meat, cheese, smoked seafood and the like.
MAP Packing/Gas Flushing
MAP or Gas Flushing can be achieved on several types of machine. Already discussed is how we modify the gas balance on Thermoformers, VFFS and HFFS machines but this can also be achieved on Vacuum Packers that are equipped with a Gas function or for bulk packs, a “Snorkel” type machine that clamps the mouth of the bag firmly while 2 snorkels inside the bag pull a vacuum and blow back a gas mix, retract out of the bag and then the bag is sealed. A prime example is the Oakham A310 pictured.
Standup Pouch Packing
High volume applications typically utilise carousel type pouch fillers and sealers. The standup pouches are loaded into a magazine from where the machine picks them up to join a carousel. Then the pouch progresses around several stations for pouch opening, pouch filling, possible gas flushing, sealing and ejection. There are specialised models for powder, liquid and retort applications.
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Spouted Pouch Packing
In much the same way as the Standup Pouch machine operates, the spouted pouch machines are generally a carousel configuration where the pouch is gripped by the neck of the spout leaving the pouch itself suspended below the carousel platform to progress around stations for vacuum, filling, gas flush, spout wash, capping and ejection. The spouted pouches are also loaded into a magazine and can come loaded on rails for easy magazine loading.
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