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I'm working on a mini project for a milk dispenser machine, using a peltier device to cool the milk down, I have to choose between a copper or aluminum cooling block (see pictures bellow).

But I'm worried about health issues in the long run, (oxidation and stuff), I have no idea what to choose.

What would you guys recommend me ?

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    $\begingroup$ What are the temperature and pressure conditions of the milk coming in and out? With Cu oxidation could occur, and I would be less inclined go with it. Al is already going to be oxidized, but Al2O3 is harder and on the outside of almost any Al product. The only downside with Al are possible correlates with neurological disorders, and that would be over lots of exposure (probably not nearly the dose from deodorant). $\endgroup$
    – Atl LED
    Aug 21, 2013 at 20:51
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    $\begingroup$ Household water is typically run in copper pipes. $\endgroup$
    – kmm
    Aug 21, 2013 at 21:26
  • $\begingroup$ @AtlLED Pressure would be gravity based, not really high, and temperature around 0°C (~32°F). The neurological thing you mentioned is scary stuff, looks like maybe copper is safer based on kmm's comment ? $\endgroup$
    – Reacen
    Aug 21, 2013 at 21:48
  • $\begingroup$ @kmm I think that copper piping is only a good solution so long as you have very clean and controlled water running through it (as is common in the US). Just searching about copper pipe corrosion show examples of where that can go bad with just water, let alone milk (see my answer). $\endgroup$
    – Atl LED
    Aug 22, 2013 at 15:59

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Assuming the answer can't be C) Stainless Steel I would go with Aluminum.

The USDA specifically mandates (1) stainless steel 300:

"Milk contact surfaces shall be made of stainless steel of the 300 series, equally corrosion-resistant non-toxic metals or heat-resistant glass."

Is the copper tinned? From what I can tell after reading some old sources (2) un-tinned copper will be corroded by milk. You have the advantage of a cool temperature lowering contamination risk (3), but many states following the FDA specifically removed the allowance of tinned copper (Sec. 22-201).

While the effects of life long dosing of Al are becoming more and more clearly tied to Alzheimer's (4), the effects build up over time. Copper has a tendency to be more acute (5) and pronounced (6, 7), and further it can tasted in low amounts and discolor the food (8). It can be said that water flows through Cu pipes, but soda is put in Al cans.

The research for this has been quite enjoyable, and led to things I didn't even think of. A alternative cleaning site has even recommended using milk to clean Cu pans.

Again so my final recommendation is to follow USDA guidelines and use stainless steel, but my second choice would be Aluminum.

Citations:

(1) USDA. 2011, July. Milk for Manufacturing Purposes and its Production and Processing.

(2) US DOC. 1917, April. STRUCTURE OF THE COATING ON TINNED SHEET COPPER IN RELATION TO A SPECIFIC CASE OF CORROSION. Technologic Papers OF THE Bureau of Standards.

(3) COMMITTEE ON COPPER IN DRINKING WATER, NATIONAL RESEARCH COUNCIL. Copper in Drinking Water. NATIONAL ACADEMY PRESS. 2000.

(4) Walton, J.R. Aluminum Involvement in the Progression of Alzheimer's Disease. Journal of Alzheimer’s Disease 35 (2013) 7–43. DOI 10.3233/JAD-121909

(5) Reilly C. The dietary significance of adventitious iron, zinc, copper and lead in domestically prepared food. Food Addit Contam. 1985 Jul-Sep;2(3):209-15.

(6) Conor Reilly. Metal Contamination of Food: Its Significance for Food Quality and Human Health. Pg 50. John Wiley & Sons, Apr 15, 2008

(8) ibid pg. 16

(7) Lee A. Price, et al. Chronic copper toxicosis presenting as liver failure in an Australian child. Pathology. 1996, Vol. 28, No. 4 , Pages 316-320 (doi:10.1080/00313029600169264)

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