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    Please give guidance on building a slow freezer (improved version)



    Hi

    I have posted this question in different forms in other threads however people have complained I haven't been clear or explained my requirements properly. I will explain my problem properly here, list my requirements and collate other peoples answers.
    Please kindly take the time to read it and tell me if I am doing the right thing, weather you foresee any problem, can give further advice etc.

    Problem: Develop a tool(proof of concept) to SLOW FREEZE chicken and cause large ice crystal damage causing excessive purge/drip.

    When chicken freezes the natural water inside the chicken(inside the chickens cells) turn into ice crystals. The freezing point for chicken is -2.2c. When a chicken freezes between the range -2.2c to -4c the internal ice crystals expand and become larger. If the ice crystals become too large they will tear/rupture the cells of the chicken and water will drip/purge out.
    If the chicken spends less time e.g. 2 hours in this range then the ice crystals will not expand so much and there will be less damage/drip. This is why domestic or any freezers have minimum freezer temps of -15c, because higher temps may cause large ice crystal damage. This is also why certain foods are blast frozen/fast frozen i.e. to cause minimal ice crystal damage.

    I want a freezer that will SLOW FREEZE chicken and maximise ice crystal damage leading to excessive purge and drip. Provided a freezer has enough capacity, as far as I'm aware, the main factors which will determine how fast a food freezes is temperature and air velocity. I am assuming that if I have control over temperature e.g. I can set as low as -2c to -5c, this will cause the chicken to spend at least several hours if not more in the -2.2c to -4c range. This being the case I am assuming a normal capacity freezer with low enough temperatures will slow freeze as I want.

    It is also worth noting that if a chicken freezes at a fluctuating temperature in the mentioned range(-2.2c to -4c) then ice crystal damage would be even greater as it causes partial freeze/thaw(aka ice recrystalization ). If possible this should be incorporated in the product.



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    Re: Please give guidance on building a slow freezer (improved version)

    Requirements/Solution

    My guess is that the best way to achieve the above is to simply get a normal domestic/commercial freezer and change the controller so that one can set temperatures as high as -2c...-5c etc. This should cause the chicken to freeze slowly and spend a lot of time between -2.2c and -5c. Perhaps I also need a function to be added which allows the temperature to fluctuate between -2 to -4c so that I can get the recrystalization. Initially this is just a proof of concept so I want it to be as cheap as possible so long as it fulfils the requirements. The requirements would be:

    1. Any cheap freezer which would be suitable
    2. Freezer must be able to set temperatures to -2c to -18c. Freezer will normally operate at -5c.
    3. Freezer sensors set up should be decent as temperature is important factor.
    4. Ideally a digital thermostat which also shows actual temp accurately, preferably real time.
    5. Freezer would have roughly 100 litres capacity.
    6. Initially I'll just put 1kg chicken in to see it works, however if it does work, I'd like to be able to support 6kg of chicken since I'd expect a 100 litre freezer to do that. Any case this is proof of concept so testing 2kg initially is fine.
    7. It should be easy to modify later so that the fluctuating cycle e.g. -2c to -4c can be incorporated. I imagine that this can be achieved provided it is frost free since there is a fan in the freezer or via installation of a heater.

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    Re: Please give guidance on building a slow freezer (improved version)

    A few questions:

    1. Given all the above, do you agree that the best thing is to get a normal 100 litre commercial freezer, change the controller to have a digital one, and put a program in for the fluctuating temperature?
    In the other threads people mentioned things like: temperature sensor with probes, meat inserted product probe, vacuum cooling, adjustable thermostat and heater, environmental chamber and vfd. However perhaps a simple freezer modification will do the job? What do you think?

    2. Am I right in thinking it must be frost free in order to maintain temperatures since other freezes will not give temperature control?

    3. Will using a frost free model allow the fluctuating cycle to be added easier as a program rather than adding in a heater which I believe would be more expensive?

    4. Can you think of any potential problems with the design e.g.
    a) I think somebody said a defrost design(which I believe is frost free) will be counter productive for ice crystal expansion, is this the case? I know it will remove from the freezer, but ice crystals developing from the cells outwards?
    b) Can you recommend a freezer that I should buy to modify? Apparently a lot of commercial freezers are mass produced with components e.g. chips that are not easily modified. I don't want to buy something that I'll then have to discard because the controller couldn't be changed or cycle program couldn't be added.
    c) will the newly modified freezer be able to maintain the set temp(or close enough) since apparently commercial freezer have a tough time doing so?
    c) If I use a cheap thermostat just to initially set temperatures, if I later want to add the fluctuating program in, will this be easy?
    d) Any other problems you foresee?

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    Re: Please give guidance on building a slow freezer (improved version)

    Guys, I apologise I know its a long read however you asked me to be as detailed as possible and I think I've given it now. I really hope you read this and will give me some guidance. I could end up spending a lot of money and end up with something that doesn't do the job after which the freezer will be useless. Based on quotes this freezer will cost me at least several hundred. However If there is a chance this will work I'd like to try it. Please help me make an informed decision, do you think the design I have suggested is a good approach?

    Also does anybody know if I can rent something from somewhere which has the temperature range I want, having searched I doubt it however probably worth mentioning anyway.

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    Re: Please give guidance on building a slow freezer (improved version)

    Technically easy, however you have flaws in your requirements, and you require a level of accuracy, that you are not going to get out of cheap components.
    If you are proving concept, and at these temps, use ice water and salt. just put your chicken in a bag, place in the water/ice solution, add salt temp will drop. very precise. as it warms add a bot more ice and a bit more salt.
    "Engineering is easy, doing for a low price is hard"

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    Re: Please give guidance on building a slow freezer (improved version)

    Duplicate post;
    Last edited by iceman31; 20-09-2013 at 03:22 AM.

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    Re: Please give guidance on building a slow freezer (improved version)

    Quote Originally Posted by mad fridgie View Post
    Technically easy, however you have flaws in your requirements
    Like what?

    and you require a level of accuracy, that you are not going to get out of cheap components.
    So how much would some decent components cost?
    Even with the cheaper components, would the freezer not stay roughly in range e.g. fluctuating from -2c to -4 and would not the sensors give a rough accuracy? I mean so long as it wasn't showing -6 when it was -2 but rather -3 or that probably wouldn't matter so much.

    If you are proving concept, and at these temps, use ice water and salt. just put your chicken in a bag, place in the water/ice solution, add salt temp will drop. very precise. as it warms add a bot more ice and a bit more salt.
    "Engineering is easy, doing for a low price is hard"
    Didn't get this please clarify. Get bucket and fill with ice cubes+salt+water solution. Then place chicken in air tight bag and put in bucket.

    How would I take the temperature of the solution in the bucket to know I was in range?
    Do you mean to say for example adding enough salt to the bucket would take the temperature down from +1c to -4c? Are you saying by adding salt to a glass of water it takes the temperature of the water down? I know it changes freezing point but not that it takes temperature down.
    Last edited by iceman31; 20-09-2013 at 03:23 AM.

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    Re: Please give guidance on building a slow freezer (improved version)

    I see the need to accurately control temperature in the range you want to work.

    Part of this would be cooling load control, the other part may need to include a heating (heat-pump component?). The two systems then work together, assisting to maintain the temp precisely where you require it to be.
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    Re: Please give guidance on building a slow freezer (improved version)

    Hi Iceman
    Thanks for clarifying and this post is in a better part of the forum.

    Back to the refrigeration cycle though - If I was attempting this I would not use temperature control as my primary control. This is too coarse!

    I would control my evaporation temperature with a suction pressure / super heat controller.
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    Re: Please give guidance on building a slow freezer (improved version)

    Quote Originally Posted by iceman31 View Post
    Like what?



    So how much would some decent components cost?
    Even with the cheaper components, would the freezer not stay roughly in range e.g. fluctuating from -2c to -4 and would not the sensors give a rough accuracy? I mean so long as it wasn't showing -6 when it was -2 but rather -3 or that probably wouldn't matter so much.



    Didn't get this please clarify. Get bucket and fill with ice cubes+salt+water solution. Then place chicken in air tight bag and put in bucket.

    How would I take the temperature of the solution in the bucket to know I was in range?
    Do you mean to say for example adding enough salt to the bucket would take the temperature down from +1c to -4c? Are you saying by adding salt to a glass of water it takes the temperature of the water down? I know it changes freezing point but not that it takes temperature down.
    You have to have temp difference for energy to flow, therefore it not just about air temp, it is about product surface temp and product internal temp.
    So to keep these small then you need air velocity over the product.
    Cheap controllers, good that they are, have limitation is accuracy and repeatably across the range, you also have the mass of the probe and thus the probes reaction time.

    Ice Salt and water, you do not need to measure the temp, the concentration will determine the temp. and is an exact science.
    So you have ice and water 0C, you add salt, the freezing point drops, so what happens to some of the ice, it melts, this done by taking heat from the surrounding water/salt mix, the brine drops in temp.

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    Re: Please give guidance on building a slow freezer (improved version)

    The smaller it is the harder it is, with this type of product.
    Another way is place you chicken in sealed container, bag aluminium box,ect), place the container in a solution (food grade glycol, salt). But the solution into your freezer, control the freezer refrigeration by the solution temperature. The solution is best agitated.
    the mass of the solution will acts as a thermal buffer, allowing for close control

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    Re: Please give guidance on building a slow freezer (improved version)

    Guys, I just want to reiterate two unanswered questions. Please answer.


    1. Would a freezer which is not frost free work? I guess no because the frost build up would not allow for decent temperature control e.g. it may cause temp to go significantly lower then set? What if I manually defrosted it few days to weekly?

    2. Regarding precise temperature control/reflection, I've put a thermometer inside my current fridge and it displays changing temperatures depending on what I change the thermostat to. If that works on a cheap fridge, in the case of my modified freezer, wouldn't you also expect it to work i.e. give me some control between the -2c to -5c range, and I'll use a thermometer to be sure? As I say it doesn't have to be bang on -2c so long as it doesn't go off by a few centigrade which would significantly change the rate of freezing. What do you think of that?
    I know I'll only know once done, however in experience or theory, wouldn't you expect that the modified functionality will give some control between the -2c to -5c range?

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