Nitrite Free Bacon: Barriers against clostridium botulinum

The development of a framework for nitrite free bacon is challenging.  Especially considerations related to botulism and preventing this food safety risk.  Due to its importance, we present our considerations and conclusions here for comment.  It is not a matter to consider on ones own.

In order to produce a nitrite free bacon, consideration must be given to:

1.  colour
2.  taste
3.  preventing clostridium botulinum toxin formation.

Colour and Taste are part of intellectual property and will not be discussed here.  Workable strategies exist to overcome these challenges.

What can not be treated as Intellectual Property is the matter of managing the risk of botulism. The broad outline presented here is from the FDA Guidance Regulation UCM252416, available for download at

Where other sources have been brought into the consideration, these are noted.  All other work is from UCM252416.

Clostridium Botulinum

“Clostridium botulism toxin formation can result in consumer illness and death.  It is the toxin responsible for botulism.”  (  By removing nitrite from the product, a significant hurdle is removed to prevent this. Nitrite allows a lower level of salt to be used. Salt and nitrite are the principal inhibitors to c. botulinum type E and non-proteolytic type B and F toxin formation. (, p 257)

We propose the following barriers:

*  Sell product frozen.

– freeze immediately after processing
–  maintain frozen during storage in production facility
–  label: “to be held frozen and thawed under refrigeration immediately before use”.
– The following additional instruction on the packaging: “Once thawed, store below 5 deg C. Consume within 2 days – 48 hours” (refer to note 1) (Peck, M. W. et al.  2006:  9, 10)

This recommendation is based on the likely average temperature in a refrigerator, the current limits on storage of chilled foods and the speed of toxin formation measured at different temperatures based on four predictive models.

The position in the UK, other European countries and internationally with respect to guidance on control of non-proteolytic C. botulinum in chilled VP/MAP foods is that the only legal requirements in the UK in relation to VP/MAP chilled foods are that they should be produced using HACCP principles, as required under European hygiene law, and that they should be stored at a maximum of 8°C (as defined in law in England, Wales and Northern Ireland), or a refrigerator, refrigerating chamber, or a cool ventilated place (as specified in regulations in Scotland).  (Peck, M. W. et al.  2006:  12)

Data on home refrigeration is based on UK figures.  No similar study exist to our knowledge for South Africa and the UK figures will be used as a guideline. Domestic refrigerators are present in >99% of households in the UK, and on average are replaced every 8 years. Refrigerators provide a key food safety device within the domestic kitchen, their correct operation will reduce the risks of the growth of food poisoning organisms in foods stored within them. Unfortunately there is a lack of recent published data on the temperatures of domestic refrigerators and the last UK domestic refrigerator survey was carried out in 1990. In order to ensure the UK has up to date information on domestic refrigerator temperatures, a new survey is required. (Peck, M. W. et al.  2006:  13)

The 1990 UK survey found that the mean domestic fridge temperature ranged from -1°C to 11°C over a 7 day period, and that the overall mean temperature was 6.6°C, with 65-70% of fridges at more than 5°C. There was variation in performance between fridges, and within each fridge over time. Different temperatures were also recorded in different parts of single fridges. Overall, for all domestic fridges the time spent at various temperatures were as follows; 28% of the time at <5.0°C, 35% of the time at 5.0-6.9°C, 28% of the time at 7.0-8.9°C, and 9% of the time at >9°C. The position appears similar in other countries, and an average temperature of 6.64°C has been reported for European fridges. It was recommended by Richmond in 1991 that the maximum temperature of domestic fridges in the UK should not exceed 5°C. (Peck, M. W. et al.  2006:  12)

A survey of consumer behaviour in France established that for short shelf life chilled products, approximately 60% of the shelf life was spent in commercial refrigeration, and 40% in domestic refrigeration. The general applicability of this to other countries is not known, given different practices in various countries.  (Peck, M. W. et al.  2006:  13)

Data from four predictive models have been considered that gives the time of toxin formation when other factors are not limiting.   All four models predict that toxin formation will occur in less than 10 days at 8°C (Fig. 1, Table 6). The different predictions of time to toxin formation reflect the different datasets on which the models were based. The model in ComBase Predictor is designed to be most robust at ≤10°C, and may give more reliable predictions in this region than the other two original models. The Skinner/Larkin model is designed to be an ultimate failsafe model. It may be that the prediction of toxin formation in 5-6 days at 8°C is the most reasonable fail-safe prediction from the models, and the prediction of toxin formation in 4 days at 8°C is the most conservative failsafe prediction. It is important to recognise, however, that these models are designed to represent various worstcase scenarios, and the issue that must be addressed is how closely predictions from these models relate to toxin production in actual chilled foods sold in the UK and elsewhere.  (Peck, M. W. et al.  2006:  16, 17)

In order to collect literature data on toxin formation in chilled foods/food materials, an extensive literature search was carried out in January 2006, and combined with articles held in the personal libraries of the authors of this report. Data extracted from 61 literature publications yielded 887 independent tests of time to toxin formation. Additionally, 27 confidential datasets that contained 420 independent tests of time to toxin formation were kindly donated by members of the food industry. This gave a total of 1307 independent tests. One independent test would typically be one product, inoculated with a defined number of spores of non-proteolytic C. botulinum (a mixture of strains), incubated at one temperature, and sampled a number of times. Replicate samples would be removed and tested for toxin at various time points (often in duplicate or triplicate), and the last time when all the replicate samples were negative, and the first time that one of the replicate samples was positive noted. Toxin would typically be detected using a mouse test, although some data were based on growth tests. All the data are therefore from “challenge tests”, where spores of non-proteolytic C. botulinum have been added to foods/food materials.

It should be noted that most of the data included in this assessment had not been generated for the purpose of evaluating the potential for growth and toxin production by non-proteolytic C. botulinum in chilled foods sold in the UK within 10 days or less at 10°C or below. The relevance of these data to short shelf-life chilled foods sold in the UK is in some cases, therefore, limited. Also, the number and proportion of positive tests is to some extent a reflection of the experimental design in the tests that have been carried out. For example, some tests have been carried out in sterile raw materials where conditions are very favourable for growth and toxin formation, while other tests have been carried in conditions not at all conducive to growth and toxin formation (e.g. preservatives added). The proportion of positive tests is a reflection of the balance between these extremes (and all intermediate positions). It is not easy to relate the number and proportion of positive tests to the safety of short shelf life chilled foods sold in the UK.

The results from 1307 independent challenge tests do, however, demonstrate that nonproteolytic C. botulinum, if present, is in some circumstances able to form toxin in foods and food materials at ≤10°C within 10 days. In total, 237 individual tests were positive for toxin formation by day 10 (19%). At 10°C, 132 of the tests were positive at day 10 (36%); at 8°C, 100 of the tests were positive at day 10 (19%); and at 4°C-7°C, five of the tests were positive (1%) (Table 7).

toxin formation

The instruction on the packaging of “store at 5 deg C; consume within 2 days (48 hours)” is then based on the assumption that the average refrigerator will not maintain a temperature of 5 deg C (probably closer to 10 deg C) and that 7% of the samples were tested positive for the toxin at 10 deg C in under 5 days.  Based on this, we suggest that the product is consumed within 48 hours after it has been thawed.

The consideration above is done on the assumption that storage time and temperature was the only consideration.  We will consider an instruction on packaging suggestion of “store at 5 deg C; consume within 4 days (96 hours)” based on all the different hurdles in combination.  We will present this for expert analysis, review and comment and after the relevant professional input, a final decision will be made.

*  Water salt phase of 20% or more.

Calculated as (% NaCl x 100/ (% + moisture) = %

Water Activity of 0.84

*  Water activity <0.85.

Method:  Drying, adding salt and other functional ingredients to bind water

* pH of < 4.6, salt at 5% wps or more

* Vacuum oxygen packaging

*  Set limits for the maximum processing time allowed for each production step and the maximum temperature allowed for the meat. (Woodys team)

The processing temperature and storage temperature suggested is 5 deg C.   Storage at temperatures of less than 3°C are generally recognised as being a means of preventing growth and toxin formation by non-proteolytic C. botulinum. In all approaches the main emphasis is on low temperature storage (not necessarily with specific limitation of shelf life). However, the specified temperatures vary. For example the Canadian and French approaches refer to 4°C as the national legal maximum, while in England, Wales and Northern Ireland this is 8°C. Further details are also given below.  (Peck, M. W. et al.  2006:  13)

The 5 deg C limit for Woodys is chosen based on the short overall processing time.  From receiving of meat till blast freezing is done in at least 36 hours.

Receiving till after injection: Within 5 hours at < 5 deg C. Temp is controlled through “ice wash” in acetic acid upon receipt (within three hours of receiving meat) and ambient temp of > 7 deg C; trimming, a second ice wash in a 2.5% acetic acid solution and then injection.
– Meat may have to rest for up to 12 hours before its tumbled due to production scheduling factors. Meat rest at < 5 deg C.
Tumbling the meat -> 3 hours cycle and allowing one hour to load the meat maintaining meat temp < 5 deg C.
(- If the meat did not rest before tumbling, the product now rests for a max of two hours at a meat temp of < 5 deg C).
– Product is smoked. Core temp in increased to at least 62.8 deg C for at least 30 minutes.  Total smoke time is expected to be 3 hours to achieve the right core temp.
– Product cools down and must reach a core temp of < 10 within 5 hours.
– Product is blast frozen to – 14 deg C. Bellys for 6 hours and other cuts for 8 hours.

Total processing time so far is 36 hours.

– Product is kept in equalizing freezer at < 7 deg C, for no longer than 48 hours.
– Product is sliced and immediately vacuum packed.
– Nitrite Free bacon is vacuum packed and frozen immediately – 10 deg C and distributed frozen.

Setting maximum time limits on each processing step as well as the overall processing time will allow us to:

– evaluate the effect of lag in terms of micro activity in each processing step;
–  evaluate the efficacy of each step in terms of any micro activity

*   NaCl 3.5% (aq) throughout a product and its components. (Peck, M. W. et al.  2006:  12)

*  Add  lysozyme and nisin as antimicrobial in the brine.  We are awaiting data from a Danish producer related to verification of efficacy and product prices and suggested dilution levels.


– the formation in a vacuum packed environment.
– every processing step must be considered in terms of possible c. botulinum formation.


– acidification step with equilibrium pH of < 4.6; a drying step;  There is not an in-package pasteurization step, a combination of cooking and hot-fill step or a retorting step.  there is a par-cooked step.
– brining step (water phase salt levels and antimicrobial’s added)
– product smoking and drying  (water phase salt levels and water activity)
– cold-smoked step should be sufficient to damage the spores and make them more susceptible to inhibition by salt. (62.8 deg C for at least 30 minutes)
– time and temperature exposure of finished product storage (refrigeration).  This must include a consideration for the storage temperature after thawing and the maximum storage time under thawed conditions.  We recommend the following additional instruction on the packaging: “Once thawed, store below 5 deg C. Consume within 5 days” (refer to note 1)  (Peck, M. W. et al.  2006:  9, 10)
–  finished product storage steps must be identified as part of CCP’s.
–  time and temperature exposure must be measured and controlled in every step.

*  note:  certain types of c. botulinum will grow at temperatures as low as 3.3 deg C.  Temp control must be particularly stringent.   Originally 3.3°C, but growth has now been demonstrated at 3.0°C .  It is suggested that meat temp be kept to < 3 deg C during processing and after processing it must be frozen.  (Peck, M. W. et al.  2006:  9) The need for this in light of the overall set of hurdles must be evaluated under review of the proposed system. –  Consider the use of a TTI. CONTROL STRATEGY ONE 1.A. Factors that are necessary to ensure that the finished product has not less than 3.5% wps or, where permitted, the combination of 3% wps and no less than 100ppm nitrite. The last is however not an option since we are looking at removing nitrite from the curing mix. Critical factors may include: – brine strength – brine to meat ratio – brining time – brining temp – thickness, texture, fat content, quality and meat type – drying time – input/ output of air temp – humidity – velocity – smoke density – drier load ESTABLISH MONITORING PROCEDURE What to monitor: – brine strength, brine to meat ratio, brining time, brining temp, thickness, texture, fat content, quality, type of meat, drying time, input/ output air temp, humidity, velocity of smoke, smoke density, drier load. OR wps HOW TO DO IT? brine strength with a salometer brine time with a clock brine temp with a thermometer and the ambient air with a continuous temperature-recording device drying time and the input/ output air temp using a continuous temperature recording device OR collect a sample and and conduct a water phase salt analysis HOW OFTEN? – brine strength – at least at the start of brining – brine time – per batch – brine temp – at the start of brining – brine to meat ratio – at the start of brining – drying time – per batch – wps – per batch IDENTIFY WHO WILL DO THE RECORDINGS ESTABLISH A CORRECTIVE ACTION PROCEDURE ESTABLISH A RECORD KEEPING SYSTEM ESTABLISH VERIFICATION PROCEDURE 1B. COLD SMOKING Critical limits – internal temp maintained > 62.8 deg C for at least 30 mins.

The following must be included:
a. Unactivated TTI receipt
b. Unactivated TTI storage
c. Application and activation of TTI
d. Freezing finished product storage

In each case:
– set critical limits
– establish monitoring procedure
– corrective action procedures
– record keeping system
– Verification procedure


Set Critical limit
– Finished product must contain statement “important, keep frozen until used, thaw under refrigeration immediately before use”
– Clear post-thawing instructions: “Once thawed, store below 5 deg C. Consume within 5 days” (refer to note 1) (Peck, M. W. et al. 2006: 9, 10)

Establish monitoring procedure
– what will be monitored
– how will it be monitored
– how often will it be monitored
– who will do the monitoring

Establish corrective action procedures

Establish record keeping system

Establish verification procedure


The strategy includes:
– brining, pickling, salting, formulation and adding antimicrobials
– frozen finished product storage

Set critical limits:
The limits used for fish:
– wfs level of > 5%, or
– pH of < 4.6, or
– water activity of < .97, or
– wps level of at least 2.4%

Establish monitoring procedure
– what will be monitored: pickling, brining, formulation (including levels of antimicrobials ans well as functional ingredients) . Including brine and acid strength; brine/ acid ratio to meat; brining and pickling time; brine and acid temperatures; thickness, texture, fat content, quality and species of fish OR wps, pH and/ or water activity of the finished product.

How will monitoring be done?
Frequency of monitoring
Who will do it

Corrective action procedures

Record keeping system

Verification procedure


1.  “In response to questions raised by a team drawing up an industry code of practice (at CCFRA), in 1995 the ACMSF revised this recommendation on the basis of a review of 31 references from the literature on the production of toxin by non-proteolytic C. botulinum within 10 days at ≤10°C in foods or food materials. The ACMSF also took account of predictions from a PC based version of Food MicroModel and unpublished data on C. botulinum (both provided by Dr. BairdParker, Unilever Research). In 1995, the ACMSF revised the second recommendation (10 day rule) to “storage at ≤5°C and a shelf-life of ≤10 days, or storage at 5°-10°C and a shelf-life of ≤5 days”.

The group involved in drawing up an industry code of practice at CCFRA, considered the recommendations of the ACMSF (made in 1992 and in 1995), and replaced the second recommendation (10 day rule) with “storage at ≤8°C and a shelf-life of ≤10 days”. The temperature of 8°C was selected as it is the legal upper limit for chilled food storage in England, Wales and Northern Ireland, rather than there being any scientific evidence regarding unsuitability of storage at 10°C. This code of practice was developed in conjunction with representatives of MAFF/Department of Health, and probably reflects much current industrial practice as it stands today, where specific controlling factors (e.g. 6 log reduction process, Aw, pH controls, other specific controls) are not present.

In response to a request from the ACMSF, in 2003 the FSA produced a draft small concise guidance document on the safe production of VP/MAP chilled foods with respect to C. botulinum. The recommendations included in this document are similar to those made by the ACMSF in 1995, and the industry code of practice in 1996, with an important difference for foods with a short shelf-life where other specific controlling factors cannot be demonstrated (10 day rule) (Table 2). At the ACMSF meeting held on 18th September 2003, the ACMSF agreed that the FSA concise document should go out to full public consultation. The consultation period ended in August 2004. The most significant issue raised by the consultation surrounded a perceived change in the “10 day rule”, and highlighted differences between the ACMSF recommendations and the industry code of practice. The different recommendations are summarised in Table 2.

storage time

At its meeting in December 2004, the ACMSF concluded that in the light of the concerns that were raised in response to the consultation, it needed to examine recent scientific evidence before advising on the FSA concise guidance document with respect to recommendations for foods with a short shelf-life where other specific controlling factors cannot be demonstrated (10 day rule). The ACMSF proposed that the FSA commission an independent review of the current scientific evidence, with the findings to be presented at a future ACMSF meeting. The purpose of this document is to provide the ACMSF with all the necessary up to date information to enable them to judge recommendations included in the FSA document on “foods with a short shelf-life where other specific controlling factors cannot be demonstrated”.  (Peck, M. W. et al.  2006:  9, 10)


All above from:

Peck, M. W. et al.  2006  Clostridium botulinum in vacuum packed (VP) and modified atmosphere packed (MAP) chilled foods.  (

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