Alcohol And Aluminum Metal Reaction
Posted 06 October 2005 - 12:28 PM
I have some recipes that involved using significant amount of wine or brandy, and would undergo cooking inside a pressure cooker at about 10 psi for half an hour. I would then simmer down the pressure cooker, open it up and then serve the dish.
The recipe has been good for me in small quantities when using a small stainless steel pressure cooker. I needed a large size pressure cooker, at least 18 qt capacity, and the only one I can get are made of anodized aluminum. It has been said by everyone in the wine and alcohol making industry that alcohol reacts with aluminum, and if so what are the reactions, and what are the products, and are there toxic products produced? The pressure cooker is anodized so I don't worry about it breaking down due to trace organic acids in the wine or brandy. I am more worried about toxic by products from reactions between alcohol and aluminum metal or other fermentation by products and aluminum metal.
Any nice folks who are knowlegeable in this area. Or at least point me to credible web sites explaining the exact chemical reactions, preferrably reputable sites with scientific credentials would be extremely appreciated.
Posted 06 October 2005 - 03:58 PM
1) Alcohol, acids, bases do react with aluminum metal. It corrodes the aluminum metal but a very good thing is happening during the corrosive reaction. The corrosion products that are formed act as a protective barrier layer, an insoluble barrier layer is formed via the oxidation of aluminum. This layer is often 200 Angstroms thick, which can reduce thermal conductivity of aluminum cooking equipment by 7%. After the initial corrosive reaction, the insoluble layer protects the aluminum from further corrosion.
2) Aluminum casks have been used in apple ciders (containing 5.5% abv):
see page 10 of 38 of this link:
Hard cider products may come in draft, keg, or bottled forms. Draught cider is
clarified and stored in wooden barrels. Keg or bottled cider is pasteurized and stored in aluminum casks. The product may or may not be carbonated. In the U.S., commercial hard ciders usually contain about 5.5% alcohol, and most are carbonated.
3) Even scientific laboratories have used aluminum caps in wine ethanol related experiments:
see page 2 of 6 of this link:
Sulfite and hydrogen peroxide treatment. Cells harvested at the end of the log
phase were resuspended in air-saturated fresh media, and 5 ml of the suspension
was placed in anaerobic sterilized pressure tubes (Bellco Glass, Inc., Vineland,
N.J.) with butyl rubber stoppers and aluminum caps. Stock solutions of sulfite or
hydrogen peroxide were added to the tubes by using syringes before they were
incubated at 308C for 2 h. When cell suspensions were treated in a different
manner, the details are given in the text. The chemistry of sulfite is very complex,
especially in a biological system. The total sulfite concentration was used
4) AND TO TOP IT ALL. Wine and beer are starting to be bottled in aluminum!
See this link:
But I can accept evidences to the contrary and will conclude for now that I can use the anodized aluminum pressure cooker very safely.
Posted 06 October 2005 - 06:41 PM
I don't know a whole lot about aluminum but I know this:
I would imagine that you aren't getting a whole lot of reaction with the aluminum in general but you may get some corrosion at elevated temps due to the acidity of the alcohol. I worked at a stainless steel company as a chemist and I can tell you that almost any stainless product would be a good choice except high carbon steel.
Any time you use metal in a aqueous medium (water, alcohol, etc..) you have metal ions forming in solution. This may or may not be what you want but it isn't going to kill you. If you can cook sauce in this stuff you can have wine in it!
Posted 06 October 2005 - 08:28 PM
The initial acidic reaction with aluminum metal is extremely fast at elevated temperature and forms the insoluble coating. I remember this explained by my teacher in Chemistry where we placed an aluminum metal bar in strong acid. However, if we pulverize the aluminum into fine powder and drop it into the acid, there was almost an explosive effect, with the very hard substance precipitating at the bottom. I think the hardest form of aluminum, known as corundum, at par with diamonds when it comes to hardness, is also the second most hardest natural mineral known to man and can be formed by accelerated oxidation. And the reaction with acids or alcohol forms aluminum oxide in the presence of oxygen. So the reaction forms a hard insoluble barrier. So unless the aluminum oxide coating are being kept rubbed off constantly as when the parts are moving, then the corrosion would be severe. However for almost no moving parts application, the coating remains intact.
Posted 07 October 2005 - 07:29 AM
Like you mentioned, I have only heard that aluminum reacts with the acidity/alcohol in wine. Even though they do, as you mentioned, brew hard cider in aluminum containers, they don't ferment wine - there are no aluminum variable fermenters to my knowledge for wine. This may be because the wine has higher acidity levels than hard cider.
As for this reasoning:
I doubt they drink the results of the experiments, so they probably aren't worried if they cause the ethanol to be poisonous or not.
Beer is put in aluminum cans, but again, it is not as high in acidity as wine. As for the wine being put in aluminum cans...well, I can't comment on this due to a general lack of knowledge (I know - it's never stopped me before ).
And of course, there's the whole alzheimers factor, where they find a higher concentration of aluminum ions in the people's brains (or something like that).
All right...I feel as though I've contributed my $0.01....
Posted 07 October 2005 - 08:21 AM
Posted 07 October 2005 - 11:12 AM
You are talking about passivation. Essentially, passivation is the removal of any impurities on the surface of the material you are working with that aid in corrosion. In the context of corrosion, passivation is the spontaneous formation of a hard surface film that inhibits further corrosion. This layer is usually an oxide or nitride that is a few atoms thick. Passivation can be seen in many different materials, my experience is with stainless steel. In the case of stainless steel, contact with a stron acid removes any surface carbon (an impurity in this case) which better protects it against corrosin. It does not prevent corrosin, only reduces the likelihood of it. There are many materials that can be used with wine production- some are better (i.e. less reactive, less succeptible to corrosion) than others. Properly passivated and cared for stainless steel is a better choice than aluminum. At a pH below 4.0, aluminum is succeptible to corrosion. The basic reason is that pH is a measure of free H atoms, and the protective layer you speak of is an oxide layer. In prolonged presence of a solution with a high free H content, the oxide layer is attacked, and water is the by product. The removal of the protective oxide layer can lead to corrosion. This is not a certainty, only a possibility. Check out the following website for more information:
Just my 1.5 cents
Posted 07 October 2005 - 12:14 PM
Posted 07 October 2005 - 12:50 PM
Maybe the question is, does aluminum oxide react with alcohol? Does it give alcohol off-flavors? I'm not a chemist, but here's two references:
If the alcohol (with the exception of methanol) is heated with aluminum oxide… an alkene is formed along with a molecule of water.
Alkenes have the general formula of CnH2n and have carbon to carbon double bonds. Ethylene is an alkene because of the double bond between the two carbon atoms. Alkenes have very offensive odors.
Posted 07 October 2005 - 01:50 PM
In order to produce the undesirable or offensive aroma, the reaction though requires something beyond my use of pressure cooker. It requires very high concentration of Alcohol (perhaps 90-95% abv), excessive amounts of Phosphoric or sulfuric acid and at elevated temperature. There is no way I am adding a 190 proof brandy alongside with very strong Phosphoric or sulfuric acid to my meat recipe.
But, will try to do research on the insolube aluminum oxide reaction with alcohol. Your information is the best one so far that is more in line with my original question. Thanks a lot!
Posted 07 October 2005 - 02:01 PM
Karl, that is true for most engines. There are significant engines already distributed that are capable of alcohol gasoline mixes such as 85E (85% Ethanol, 15% gasoline) and even 95E. The main reason why corrosion is a problem with most engines that have aluminum is that these are moving parts, subject to wear and tear, removing the protective layer due to friction and other physical forces.
But for wine making, it is very passive, unless you vigorously clean the equipments with a diamond or steel brushes, then that too will hasten corrosion, but I don't think that steam cleaning (SIP) is enough to remove the protective layer in most wine applications.
In other words, I agree with what you said.
Posted 07 October 2005 - 03:27 PM
Posted 07 October 2005 - 04:01 PM
Posted 07 October 2005 - 04:53 PM
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