[thedoc (OP)]

aashishdiayar asked the Naked Scientists:
   
Hi

I am doing an experiment to test the electrolyte concentration in different energy drinks, cool drinks and juices. I am also testing whether temperature or storage (can or bottle) will affect it. We expected the bottles to have a lower electrolyte concentration as the cans would release ions into the drink however our results showed that the cans had less electrolytes than the bottles in all our tests. Can you explain this?

Many thanks,
Aashish

What do you think?

[cheryl j]

If the cans released ions, would they form bonds with ions already in the drink?

[evan_au]

Can you provide some more information, please?

• What are you studying? The drink itself, or the effect of the container on the drink?
• Are we talking about plastic bottles or glass bottles?
• Are you comparing the same drink in a glass bottle, plastic bottle and aluminium can? (I haven't seen many drinks sold in all 3 container types..)
• How are you measuring electrolytes? (eg conductivity or chemical analysis or ??)
• What type of electrolytes can you distinguish? Different salts, acids, carbonic acid ("fizz"), etc?
• Are you comparing a sugary carbonated drink or a caffeine energy drink (which may not have many ions in solution) or an acidic cola drink (the acid could show up as an electrolyte), or a sports energy drink (which has intentional electrolytes added to restore body salts lost to sweat during intense exercise)?
• Do you record the pH (acidity) of the drink?
• Do the cans have a plastic "liner", sometimes used with more acidic drinks?
• Do you test it straight after opening, or do you let it stand to let it go "flat" before testing it?

My expectation is that:

• Glass bottles are chemically inert, and should not leach ions into the drink
• Plastic bottles may leach organic compounds into the drink, but probably not ions
• Aluminium cans could dissolve some aluminium into the drink, but aluminium is protected by a thin, transparent (invisible) layer of aluminium oxide, which reduces this.
• Some types of containers would stand a higher pressure of carbon dioxide than others, which may show up as an electrolyte if you tested it straight after opening.
• Sports rehydration drinks would tend to come in resealable plastic bottles because cans are not resealable, and glass bottles are heavier (and could smash if you fell over: safety issue).

The best way to do this comparison is to look at the same kind of drink from the same manufacturer, sold in different containers. Failing this, buy containers of different types and fill them with drink from the same source, and let them stand for a few days (covered) to absorb any ions from the container, then test them.

[Bored chemist]

If the cans (or bottles) were releasing ions into the drink then they would dissolve and you would probably complain to the manufacturer.
Drinks cans are (as far as I know) always varnished on the insides.

[SeanB]

BC is correct, most steel and aluminium cans are internally coated with a varnish during manufacture, to prevent unwanted contamination of the product. This is a surprisingly good coat, and often you will find a steel can that has been wet, but protected from abrasion, will have an undamaged and rust free interior and exterior after years of submersion.

You might find the variability you measure is more due to the various batches being slightly different due to aging and being bottled by different plants. The major control is invariable to have a consistent colour, density and taste, and different plants can have slight variation in this, each producing a single package type per batch.

[james oliver]

Stay away from energy drinks - its all crappy sugar. After a workout, if you want/ need to replenish anything, have some water and fruits and veggies. Some nuts are good as well. Fruits have sugar but accompanied by real nutrients, including electrolytes.