The Role of Preconditioning in Food and Feed Extrusion
Published:March 17, 2021
Summary
What Is Preconditioning? Preconditioning means to condition or prepare a material before it is processed further. In the context of extrusion processes, preconditioning occurs just prior to extrusion inside a piece of equipment called a preconditioner. The preconditioned raw material exits the preconditioner and moves into the extruder for further processing down the line. The dry raw mat...
Good information. As always, the effects of preconditioning cannot really be divorced entirely from extrusion, which finishes the cooking process. And, ultimately, how all of this affects the end material is what matters.
Thanks, professor Michael Joseph, for keeping us awake on the preconditioning and extrusion principles...Is a very good overview useful to teach to our operators and apprentices...
Important discusion about the preconditioner design results in a very important conclusions for the operation.
As preconditioner is an special " mixer" it will be important to know opinions on what is the most important in the design.
Parameters like, level of operation, time of retention range, one or two axes, sens of rotation of two axes, how to inyect the water and the steam, position of beaters at the inlet, in the middle and in the outlet, rotation speed, etc.
Because of mixing water, flours and steam is a complicated operation, is very important to built an homogeneous mix and to get that, it needs to pay atention to some details, as for example; how to avoid the wet flour to stick on the walls of preconditioner and after that to hook off and to cause problems at the extruder....( is an example in a tipical instalation of petfoods production)
Once we know about the principles and objectives of preconditioning I feel that the following discussion is about the preconditioner designs and operation of this machine.
Id like to hear your opinions.
Thanks for your comments, Ignacio. You raise some important points. While there are several designs of preconditioners available, the predominant idea with those designs is to have maximum contact of the dry raw materials with that of water and steam to quickly create a precooked material.
As far as wetting of the flour to the walls of preconditioner is concerned, it's probably due to the difference in surface energy between water and the preconditioner walls (metal). Water has low surface energy than metal. As such water (water with raw materials) sticks to the metal and not vice-versa.
I think to reduce the sticking, probably the metal surface must be coated with a material that has less surface energy than water. That's my understanding about this issue.
This might not be an intelligent question but I'd like to know why in the conclusion you've written that preconditioners mix the raw materials "uniformly", why wasn't the word homogeneous used? These words are used interchangeably in a lot of places so I found it interesting if there's a specific reason for this word selection.
@Haneea Ahmad... That is a good observation and as both the words 'uniformly' and 'homogenous' are used interchangeably, I did choose one word over the other without giving much thought.
Most of the content that I looked up after your observation have referred to both these words almost in a similar way. However, on the site physics.stackexchange.com, the following was mentioned:
"The general meaning of 'homogeneous' is: of the same kind; alike; consisting of parts all of the same kind. And the general meaning of 'uniform': remaining the same in all cases and at all times; unchanging in form or character."
If someone else has any inputs on this, it is welcome.
@Haneea Ahmad from our point of view the word uniformly was used as sinonimous of homogeneous, this, in my latin special interpretation.....i agree with the word homogeneous....
Depending on the raw material, conditioning is recommended for 2 to 4 minutes in a sealed container at a temperature of 100 degrees Celsius and a pressure of 2 kg/cm2 where the composition does not change.
