Thermal Process Validation Cooker Characterisation Temperature Distribution vs Heat Distribution

Transcription

1 Thermal Process Validation Cooker Characterisation Temperature Distribution vs Heat Distribution Graham Bown, Thermal Process Specialist Food Manufacturing Technology: Process Support HPF MIG: 28 Jan 2016

2 The Issue Cooking assumes the same thermal process is delivered to each particulate / container so even-heating is a pre-requisite to satisfactory pasteurising and sterilising Applies to all cooking vessels including closed pasteurisers and sterilisers; batch and continuous (meat ovens, retorts, hydrostats etc) Closed cookers that contain air must avoid static air or air pockets to ensure heat transfer rates (to the product) are the same throughout the cooker Traditionally determined by studying temperature distribution throughout the cooker (eg, minimum 5 strategic points per retort basket) But air can be at the correct temperature and may only deliver 1/100 th to 1/1,000th of the energy otherwise delivered by the heating medium (steam, superheat water etc) So measuring temperature environment may not detect low heat transfer rates!

3 A Solution Measure the rate of heat transfer throughout the cooker Applied by measuring f h 1 throughout the cooker Has the advantage of indicating heat transfer rate with time throughout the cook Uses product simulants to avoid variables associated with real products and complex packages Uses lots of loggers 1: f h is the time taken to reduce the temperature difference between the heating temperature and a measured point, buy a factor of 10

4 Impact of air on f h in 3 retort styles Ongoing lab trials using PP blocks and identical loggers have shown: Style Time / temp Pressure % air 1 f h Time to F 0 >3min Pure steam Steam / air Raining Water 121.1C No over pressure None (!) 20.7min 25.9min 1.5bg 18% 21.7min 27.1min 3.0bg 49% 22.2min 27.8min 1.5bg 18% 21.2min 26.2min 3.0bg 49%?? Observations, in this instance: Presence of air reduces heat transfer rates (extends f h ) Presence of 49% air extends time to F 0 >3min by 1.9min all else equal Difficult to calculate f h (and j) consistently subjective asymptote selection based on the same Pure Steam time / temperature profile - using CTemp to calculate lethality for different f h values 1: Daulton s laws of partial pressure

5 Temperature vs Heat distribution Temperature Temperature with position and time Sensitive to time Limited use beyond first 5 min Relative to SP & MTI Indicates venting performance Heat Heat transfer rates with position and time Integrates over cycle Sensitive only during constant cooker temp Sensitive to cooker performance Calculations can be subjective Heat distribution Temperature distribution

6 Why now and Why us? US FDA is requesting Heat Distribution from those who use Steam /Air retorts, to support process filings both internally in the USA and from those that export to the USA IFTPS has issued a series of Thermal Process Protocols 1 including one for Heat Distribution to apply to all cookers that do not use pure steam (including Raining water and water spray retorts) US FDA may be about to adopt the IFTPS protocols EU directives re HACCP and English law Due Diligence defence suggest the need to evaluate and perhaps mitigate against the risks of air within cookers No evidence of food safety incidents due to entrapped / uncontrolled air probably because of the high level of industry awareness and good retort design 1: Guidelines For Conducting Thermal Processing Studies, IFTPS (2014)

7 Heat Distribution IFTPS: Experimental design Study minimum 5 points per basket positions as Temp Distribution Study all baskets per retort cycle At last 2 retort cycles (same start point, load, IT) Study full load and all permitted part load arrangements Include loggers at MTI & control probe & close to the fan (steam / air) Corroborate with pressure and heating media flowrates 5 basket retort requires at least 53 loggers!

8 Heat Distribution IFTPS: Success criteria To verify all positions are equal: Prior temperature distribution ΔT<±0.5 C Per retort: f h %CV 5% 1 (note: from a minimum of 2 cycles) If %CV>5%: Check accuracy, placement etc Run further trials Remedial engineering to improve slowest to heat location Slowest to heat location is the place to conduct heat penetration studies If %CV>5% and can t be improved: Slowest to heat location is the place to conduct heat penetration studies 1: %Coefficient of variance = σ x 100

9 Some issues Compliant temperature distribution is a prerequisite May double the data analysis required Requires the use of a simulant (bentonite, silicones, plastics) Requires works to demonstrate simulant function Involves additional costs and effort Logger conduction errors can become significant (impact on f h ) ComSol modelling accounts for errors associated with loggers with different length probes

10 A Campden View with your help - please FMT-PS is preparing a view on Heat Distribution: Should it / can it replace Temperature Distribution? Are the US FDA concerns real and appropriate in an EU context? Can the IFTPS protocols be implemented practically? Review Success criteria in a practical context (experimental error?) Does it change our view on cooker control and design? How to relate previous successful Temperature Distribution studies and reconcile differences with results from Heat Distribution studies? We will appreciate your inputs please - so we can represent an Industrial perspective Flora and Graham are to speak to the 2016 IFTPS Conference in 4 weeks Have you already had some experience with Heat Distribution that you can share with us - please? What do you need to know about Heat Distribution? Can we help?

11 IFTPS protocol: Comments so far Use actual retorts to perform heat penetration trials, loaded under actual conditions, using worst-case actual products packed in actual packaging under actual conditions. Use local environment loggers adjacent to every simulant block Use identical loggers in identical simulant blocks designed to reflect product f h Are 5 strategically placed simulants in each product stack enough? Are 2 or 3 replicate trials enough? Protocol applies equally to all cooker types that contain air by design or by poor practice (eg poorly vented steam retorts) Re-validate if programmed pressure changes or if product response to pressure changes (eg pouch geometry via filling conditions) Even carefully regulated trials produce %CV>1% amongst the blocks so consider extending cooker allowance in success criteria Need non-subjective method to calculate f h and estimate j

12 Timetable: Commit IFTPS paper 12 February (!) Draft White Paper: Heat Distribution: A Campden perspective IFTPS conference 23 to 25 February 29 April Presentation at next MIG 26 May Publish White Paper 30 June Appreciate any contributions during the next 2 weeks - please: graham.bown@campdenbri.co.uk