Extrusion is a process where the objective is to achieve cooking of the mixture of raw materials and ingredients, shaping it into a croquette. Cold extrusion, however, differs. The temperature of the food does not increase, and products with high density and humidity are produced – such as cookies, muffins or sweet. The primary difference between ordinary extrusion and cold extrusion rests in the temperature.
In traditional extrusion, more than 100 degrees celsius is required to achieve desired results. Currently, cold extrusion is applied internationally for the production of a number of products, such as sweets, supplements and medicines. These can be obtained in different forms, such as: cool, damp, half damp, dry, freeze-dried and dehydrated.
Contextualising this process in the petfood industry
This process is gaining popularity as consumer preferences shift to products processed at lower temperatures to maintain nutritional value. Its growth is also related to the increase in demand for pellets, which is a result of the growing need of owners to provide their pets with more quality and nutritional content, not only in balanced feed, but also in sweets, snacks and supplements.
Brief explanation of the cold extrusion process
The idea behind cold extrusion, is to form a dough in the shape of a tube or dense rope from the extruder of a diameter close to the one desired for the finished product. These ‘strings’ of product that come out of the extruder are transported to a machine that turns them into small granules, which will subsequently be subjected to the drying process.
Advantage of using cold extrusion
One of the main advantages of this particular extrusion process is that it can be used to handle heat sensitive ingredients and components, as can be the case with some vitamins and minerals.
Cold extrusion is used for the manufacturing of products where it is necessary to complete the product before the cooking or drying processes. This could be, for instance, the cold extrusion of a co-product or a product with high, fresh meat content. With cold extrusion, it is possible to control the reduction in pH (preventing certain microbes and pathogenic bacteria from replicating), which provides a stable pH level to avoid reactions such as protein denaturation, moisture purging or discolouration. Ingredients with high levels of protein, amino acids, fats and fatty acids experience a reduction in pH when processing the matrix thermally.
Additionally, this process avoids using water, an element that increases the chances of producing yeast and/or mould. Because of this, a considerable amount of preservatives are added to ensure an expiration date of 24 months.
Some ingredients and raw materials that are used for cold extrusion products are pieces, bone material, fish liver and/or lungs, pigs, cows and poultry.
To summarise, the advantages of cold extrusion are:
- Nutrients are not subject to high levels of mechanical shear and temperature, maximising nutrient supply and minimising costs, as hot extrusion adds nutrients to compensate for damage caused during the process
- Crumbs can be obtained in an easier way as heat damage does not occur
- Final product cost is reduced by lower use of energy and other inputs
- A greater quantity of wet ingredients can be incorporated, allowing for the use of more fresh ingredients
- A lower level of lipid oxidation is obtained, making the final product more nutritious and durable
- There is the possibility of joining two formulas in response to the needs of a particular species or breed
- In carnivorous species feed, it is not necessary to use starchy ingredients, thus reducing feed costs
Disadvantages of cold extrusion
One of the main challenges cold extrusion faces, is the temperature of the material being extruded, which can affect the viscosity or consistency of the product, and therefore its ability to maintain its shape.
On the other hand, you need to pay special attention, in order to not lose the stability and moisture of fresh meat before processing begins. This can happen due to time delays between processing, extrusion, and the final cooking of the product. In terms of post-extrusion and processing stability, it is essential to control oxidative reduction and associated reactions prior to final cooking.
Conclusion
Cold extrusion presents the opportunity to create more profitable products providing better nutritional quality and, in turn, contribute to a more sustainable aquaculture industry, by improving the health of different species. This process can prove very challenging depending on the desired formula and nutrient goals in the finished product. Undoubtedly, companies and producers of sweets, supplements, and snacks for the petfood industry that adopt cold extrusion, will be opening a wide range of possibilities with innovative, nutritional, and sustainable products.