Topics of the month include hammermills, unadulterated products, the extruder barrel and organic and/or functional petfoods – quite a range, so let’s get started with hammermills.

Grinding petfoods is typically done with hammermills as some plant’s pre-grind ingredients upon receipt at the plant and an example is whole corn and other grains. Usually once all ingredients are received and a mix or batch is weighed it then goes to final grinding.

The final grind hammermill yields the final mix going to the extrusion cooker. The exception might be the micro ingredients which can be added before the final mixer right after this final grinding step.

What should be expected of the hammermill? The extrusion process, including the preconditioner, is where moisture and steam are added, and pressure increased so as to get the degree of expansion out of the final die.

Grinding reduces particle size which is an important part of the process. The idea is to have as even particle size as possible, no fines and no oversized particles to be exact. Ground mash is sieved and graphed to produce a tight, vertical, bell curve where most of the materials is relatively of the same particle size.

The typical grinding result chart (Table 1) shows an effective grind, most of the materials is on the three middle sieves. Low overs and relatively low fines when you consider the process. The preconditioning process as well as the extrusion process is enhanced when low flour levels or low large particles are present.

The moisture and steam added is more effectively and evenly absorbed yielding a better control on expansion and product appearance. The finer the grind the prettier the kibbles appearance, simply shift the curve to a smaller average particle size.

Hammermill grinding is a science on its own and designs vary therefore it is recommended to do test grinding of your possible formulas to visually see the results you will have in your process.

Screen sizes in terms of openings, hammer hardness, the number of hammers as well as the speed in RPM’s or the tip speed are all critical factors in grinding efficiency.

Air assistance packages moving air through the screen is also effective in hammermill operations keeping the screen clean lowering the temperature and promoting capacity through the mill.

A rather big topic

Due to regulations in salmonella levels in finished products, unadulterated petfoods has once again become a rather big topic recently. The bacteria normally seen in some raw materials will always be present. There are tests in some cases to determine their presence before processing such as tests for mycotoxins.

Foss recently developed a test for this with their equipment. Melamine was another historic topic and a test for this is also possible. The extrusion process when making petfoods can and does have the ability to eliminate many non-desirable elements.

Dr Daniel Fung in January of 2008 in the ‘Synopsis of Food Microbiology’ Seminar reported that bacteria at 77°C, yeast spores at 95°C, mould spores at 104°C and bacteria spores at 125°C are eliminated if that temperature is reached.

In petfood extrusion this is where the term critical control points developed and the technology to monitor the temperature at different locations became apparent. Exiting the conditioning cylinder at 77°C is relatively easy, controlled if a slide gate is programs to stay closed until this temperature is achieved.

At the end of the extruder barrel 125°C is also not so hard to do with a properly located probe checking temperature and by passes the product until the temperature is reached. All of this is also greatly assisted by the existing and advancing computer controls in extrusion.

Most of the undesirable elements are critical or survive the process when starting and stopping the extrusion process, once heated up the standards are usually easily met. It should be noted that Extru-Tech Inc has a verified validation kill step with their process. It should also be noted Wenger did 770 or so tests on salmonella elimination years ago, salmonella added to the formula and tested post extrusion and not one sample was positive.

Having said this the key is not infecting the extruded product post extrusion. A totally different topic, plant design to effectively keeping the sanitised clean product from contacting any bacteria before packaging. The reason for all of this is regulations so as pet owners do not handle petfoods that contain salmonella. Separation of the plant in terms of personnel and airflow control in areas of production are a big part of new plant designs.

Growing at a rapid pace

Organic and or functional petfoods have been growing at a rapid pace. These would be petfoods made from natural organic sources, much like human foods. There are regulations of organic petfoods. In order for a petfood to be labelled as certified organic, USDA ORGANIC, it must contain at least 95 percent organic ingredients.

Petfoods sold as organic without the USDA label are considered partially organic which means the food contains some organic ingredients. There is allot of information out there on the web regarding this topic.

The USDA Organic Regulations website: https://mymag.info/e/1680 is a good start for a search on organic regulations.

An example would be use of free-range chicken meat as an ingredient source with no antibiotics used raising these chickens. Traceability of ingredients is a topic that is needed when claims are made so as to prove the ingredient source.

Providing some sort of health benefit

Functional petfoods are products that contain what are called functional ingredients. Ingredients that provide some sort of health benefit to the pet while meeting the nutritional needs of the animal.

Ingredients such as prebiotic fibres, bacteria, omega 3 fatty acids, probiotics and others such as beet pulp, fruits, vegetables, whole grains, glucosamine are examples of what to see on the label for functional foods.

These ingredients tend to assist in many pet situations such as age and mobility, but most are designed for intestinal modifications for aiding digestions or weight loss as examples. Let’s discuss the extruder barrel in the troubleshooting section.

Article contributed by Joe Kearns, Editor, International Petfood Magazine.