Shelf life of chilled food

The words used for the shelf life of food after production are either  ‘Use By’ or ‘Best Before’ in the UK. We are looking at chilled shelf life products or fresh products in this blog. These have the “Use By” shelf life which is all about food safety. These products are more likely to be excellent places for pathogens, or disease causing micro organisms to grow, in the right circumstance. They are often referred to as “High risk”, because the risk of illness is higher. They are produced in “high care” areas for that very reason.

food microbiology

High Risk Products

As you can imagine, if you are producing a High-Risk product, there will be more extensive microbiological testing to be carried out.

High Risk products include Ready to Eat (RTE) Chilled products. Long life products such as canned, vacuum packed and jarred foods also need specialised microbiological testing due to the Clostridium risk, especially botulinum (which causes botulism and is very resistant to heat, dessication and thrives in no oxygen atmospheres). C.botulinum can have extremely nasty consequences. Botox is derived from the botulinum organism and works by paralysing the muscles where it is used. Botulism does the same, but in a more systemic way. 

 

Microbiological risks for chilled shelf life

There are many microbiological considerations. Firstly, you need to consider all of the ingredients you are using and the microbiological risks which apply to them. For example, chicken you may consider Salmonella spp, Campylobacter spp and Clostridium perfringens. But these “bugs” are not just in chicken and eggs, but also other raw materials such as nuts, cocoa beans, veg and fruits.

E. coli, you may know comes from animal’s (and human) intestines. It can also be found in raw milk or even contaminated vegetables. So perhaps there are some ingredients which you might not expect to be at risk from these pathogens. 

shelf life chilled part two
hand washing

More pathogens 

Staphylococcus aureus comes from human and animals’ skin. Humans can be carriers of S.aureus, and if they are, and they are handling your product, at any stage of processing a product, where the product is open to handling, they could potentially contaminate it. Personal hygiene is of utmost importance. There are many carriers of this pathogen so it cannot be eliminated from the population, and it varies during the year too. In winter, the incidence goes up, and in summer it goes down. In some food production sites, there are routine hand hygiene swabs taken and one of the tests is for S.aureus .At these sites, the company policy is often that anyone who is a carrier is moved to an area where the food is already packed, such as despatch

Risks abound

Consider all of the microbiological risks that are posed to your finished product, from raw materials to people to the environment to the processing. Get specifications from your suppliers. If you are aiming for SALSA or BRCGS accreditation, this is a “must have”. Ensure that they are read and understood, not just filed away. Check incoming raw materials against the specification and agree it in any case with your supplier.

In addition to the pathogens, you need to consider spoilage and the packaging that you use for the finished product. The type of packaging will make the product shelf life vary. Every time you change an ingredient or packaging, any element of your product, you must test again.

microbiology
training records

Any microbiological tests must be carried out with the correct storage conditions in mind. The law in the UK states that you have to state storage conditions on the pack for the consumer to follow, where this is important for product safety. The shelf life data from your tests will back up the stated durability coding or shelf life.

In my opinion, accelerated shelf life testing is not a valuable set of data. The conditions do not reflect those in real life.

It is an extremely good idea to get an expert to help you define the testing required, as it is so important to get it right.

The limits for Ready to Eat products are stated in this publication from the Health Protection Agency:

‘Guidelines for Assessing the Microbiological Safety of Ready-to-Eat Foods Placed on the Market’

Organoleptic testing

You should carry out Organoleptic Testing when developing a new product, then at the very least annually thereafter for each finished product. Photographs can help with reviews too. High risk products should have this type of assessment carried out on them. This is in addition to microbiological shelf life testing.

It may be necessary to keep a sample of each batch of product you make. This is in case of quality or food safety complaints. Organoleptic Testing more frequently than annually, is best practice, and also gives your team experience in monitoring quality .It can be a great time to discuss other issues too. Try to include someone from each area of the production. The frequency depends on how many SKUs you have. A schedule of testing will help ensure that all SKUs are captured.

You need to record your testing, Record the product, batch, the shelf life you applied, then carry out testing from the Date of Production (DOP) + however many days or weeks is appropriate for your product type. For the first assessment, go beyond the anticipated shelf life test if the product is still safe and palatable. Record scores for pass / borderline / unacceptable, for each sensory test that you perform.