Achieving a desirable shelf life for ambient stable bakery is not necessarily a simple process, as microbial hazards come in all shapes and forms – and the protection needed depends on the goods themselves. Andy Walker of Premier Analytical Services (PAS) offers insights into what works well and what not so well.

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Bakery goods cover a wide range of product types and these have a correspondingly wide range of robustness when it comes to microbial hazards.

Some, such as long-life ambient cakes – which are controlled inherently by recipes designed to lower the water activity – are very resilient and perform well in the marketplace.

However, controls available can be limited or more challenging for other product types, such as hotplate goods and standard bread loaves, while still achieving quality, taste, texture and other attributes desired by consumers and retailers.

While these products have had, and continue to have, a very good microbiological safety record, there does need to be recognition of how this has been achieved, with an understanding of the science behind the controls. This is to avoid mistakes when striving for longer shelf life and changes to processes.

Here, Premier Analytical Services’ Andy Walker discusses some of the microbiological hazards and control strategies that need to be adhered to in order to keep such a staple product safe for consumers.

Hazards defined

So, what are these hazards and why can they be a concern if not controlled in bread and hot plate goods?

The incidence of pathogens such as Salmonella remains a risk. In addition, incidences1 of Shiga toxin producing E.coli (STECs) in raw flours and recurring food poisoning outbreaks2,3 in raw dough products such as cookie dough serve to support such concerns. The key control is heat, as Walker comments: “Thankfully, such a control is inherent in the bread baking process, so it is not possible to form the desired bread structure without eliminating such pathogens. However, the next job for the food quality team is to protect post-baked bread from contamination from raw flour, which is of course plentiful in bakeries.”

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Nowadays, any post-bake flour used is heat-treated to ensure that food safety4 can be assured. This treatment of the flours should be validated to demonstrate the absence of vegetative pathogens.

Next, bakeries need to consider the level of airborne contamination from raw flour. This can be started off through asking simple questions such as, “What is stopping the air flow, or the direction of air transfer, from moving flour from pre- to post-bake areas?”

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It is therefore essential to measure air flows and air pressures across a bakery where there is no physical segregation between pre- and post-bake areas.

Such information can also help start to assess the number one microbiological shelf life limiter – mould. Air movement is a mainstay of a carefully designed and executed mould survey strategy, which takes place across the plant and environment. Such surveys are key to understand how to reduce mould complaints in ‘at-risk’ bakery products.

Hotplate goods, including crumpets, muffins and scotch pancakes for example, do not have the luxury of an inherent thermal kill for vegetative pathogens – these can pass a general product quality check without achieving adequate bacterial kill, so careful maintenance of plant is essential and regular temperature monitoring required.

Vegetative pathogens are far from the only hazard of potential concern, though. There are other pathogens that can produce toxins in vulnerable products, including various Bacillus species and Coagulase positive staphylococci. The former can be inherently controlled in bread through the use of preservatives, such as vinegar inclusion or calcium propionates (E282), which help extend shelf life by interfering with the growth of microorganisms. However, these have little or no effect on the latter, which rely on management and procedures control from food handlers to mitigate the risk.

“There is a misperception that propionates are the magic bullet in the war on moulds. While they can have some effect, their key impact is on Bacillus”

So, preservatives play a valuable role in the bakery industry, provided that they are used correctly. However, it is important to know which preservatives target which hazards. There is a misperception that propionates are the magic bullet in the war on moulds. While they can have some effect, their key impact is on Bacillus, as detailed above.

Sorbate, however, is much more of a controlling preservative against moulds and also yeasts. If used as directed, introduced at the correct stage of the process by mixing into the water phase before any acidic ingredients are added, and at the correct level, it can have a huge impact on enabling an increase in the shelf life. While sorbate is most effective in acidic products, products with a pH close to neutral can also benefit from this preservative.

The problem with moulds

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When it comes to moulds, however, because of their ubiquitous presence, even with diligent hygiene teams and the application of controls recommended from mould surveys, there is still only so much that can be achieved; there comes a point when, as shelf life increases, the failure rate due to mould growth also does. This is due to the difficulty in completely controlling the environment and the need to hold post-baked product within that environment during the cooling stage and prior to packing. During this time, any mould contamination can be exacerbated when applying forced cooling air over the product.

A range of so-called solutions for mould contamination are often considered. However, an understanding of the problem and how solutions work is essential to determine if they are viable, practical and an effective use of resource.

The use of UV light, for example, is frequently recommended as it is known that UV damages nucleic acids, so will successfully kill moulds that are exposed to the UV light. However, the shape of the surface of bakery products can create valleys which are effectively in shadow and, as such, any mould spores can be hidden from the UV and thus protected.

Outside the UK, the use of a pasteurisation step post-packing is used. This has an incredible impact on mould-free shelf life but at a cost; heat-resistant packaging can be expensive, and the secondary heat input is usually considered cost-prohibitive for the UK market. It’s also worth noting that this treatment only serves to protect the shelf life while sealed. Once opened by the consumer, the clock starts ticking again.

The use of modified atmosphere packaging can also be very effective against mould, provided it is used correctly with low oxygen permeable packaging and effective seal integrity. Also, there is a need to pull a slight vacuum to remove the trapped air within the bread structure from equilibrating in the packaging headspace and removing the control. This leads to added cost, as well as decreased throughput through the plant.

In theory, the reduction of oxygen introduces the need to consider the potential risk of botulism. However, such products have a long and healthy place in the market, such that this hazard is not realised in this sector of the food industry.

All of these hazards require an ongoing series of control strategies, including elimination (killing the microbes), inhibition (slowing or stopping their growth) and – the hardest of them all – exclusion (stopping recontamination).

Despite all of this, the bakery industry continues to have a rightful place as producing high volumes of safe food despite the ever-increasing burden of price reductions and squeezed margins, minimising the ability to invest in such an important sector.

This article hopefully provides an insight into just a few of those hazards and the ongoing hard work required to feed the nation with this essential, but not so robust, foodstuff.

To discuss more about shelf-life protection of your bakery goods, please email

Journal: S. Crowe et al. Shiga toxin-producing E. coli infections associated with flour. The New England Journal of Medicine, Vol. 377, November 23, 2017. doi:10.1056/NEJMoa1615910. Regulation (EC) No 178/2002 general principles and requirements of food law