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Why should corners be avoided in food manufacturing

FoodSafetycylindrical tanks Design Equipment Manufactering Risk

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Posted 07 December 2016 - 12:16 PM

Hallo IFSQN members,


I have a pretty simple question. Why should you prevent corners (example: square tank) in your design for food manufacturing for a viscous food paste product (like peanut butter and choco paste). 


I've found some minor information that round (cylindrical) tank is better to use because it's easier to clean and sanitize but I've not found better and more accurate information (the science behind it). And If you have corners in your design, is there a critical limit for this until is not consider safe? Is this something that can be calculated with a equation? 


Thank you for your time reading my Topic.





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Posted 07 December 2016 - 03:52 PM



You're correct in that it's a cleaning issue. It's also linked to viscous flow in that sharp edges cause turbulence in low viscosity flow and other challenges for high viscosity flow. You can get product trapped during normal operations causing thermal issues, and viscosity is usually related to temperature in food products. Thus on a long production run you can also experience blockages as the more viscous material cools and slows the flow.

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Posted 16 December 2016 - 06:03 AM

Yes, corners are considered "hard to clean" areas of equipment so they are best to be avoided.  It also can be a spot where product is stagnant during processing/production.

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Posted 01 January 2017 - 01:57 AM

Hi Henrietta,


Yes, as the other responders said, the corners (properly "Internal corners") are important due to ease of cleaning and 'dead zones' in product flow.


Regarding your request for specific science and calculations, the generally accepted industry convention for internal corners that are considered to be cleanable and acceptable in a food contact area is a radius of 3 mm.  This means that the internal corner should be rounded off to a smooth curved shape.  If you want to measure the radius of an internal corner, draw a circle of radius 3 mm in the corner of a piece of card.  Using the circle as a guide, cut off the sharp square corner of the card, which will result in a rounded corner.  Put the rounded part of the card into the corner of the food equipment, perpendicular to the 'walls' of the equipment.  If the corner of the card doesn't fit into the corner of the equipment it is too square to be easily cleaned and shouldn't be used in food contact areas or 'splash and spill' zones of food facilities.


The comments above are generic, not specific to any type of equipment or liquid.  For viscous products a cylindrical tank is probably better than a rectangular tank; the product will probably empty out better and it will be much easier to clean and sanitise than a rectangular container, even one with rounded internal corners.   


There is a European non-profit organisation called EHEDG that provide excellent guidance on this topic.  You can find their guidance documents at http://www.ehedg.org/guidelines/.  I recommend document 8 "Hygienic Equipment Design Criteria" which is free to download.




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Posted 02 January 2017 - 10:33 PM

I agree with what has been said previously. I would also add that a suitable cleaning validation programme (e.g. microbiological) should be acceptable if a cylindrical unit is not immediately available for a valid reason, but the solution is to engineer the problem out. Unfortunately I cannot comment on viscosity or quality issues as it is not an area I am particularly familiar with.

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Posted 23 May 2018 - 01:43 PM



If you really want to get scientific/technical about it, you can try using Bernoulli's Equation to model the flow, this will

allow you to quatitively analyse the effect on the velocity of the fluid before and after passing the 

"curvature" of the tank . You can even compare calculations from the square corner to the curved to justify your decsisions.

The modelling can also be used to establish your own in-house critical limits of the flow rate within the tanks to

prevent build up of material.



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