What are the metallic looking spots that float on top of my iced tea?

August 21, 2008 10:40 AM

What are the metallic looking spots that float on top of my iced tea?

So I got an iced tea maker, and if I have leftovers at the end of the day, I put the pitcher into the refrigerator. The next day, the tea develops metallic looking spots which float on top of the iced tea. What are those?

posted by realpseudonym to Food & Drink (12 answers total)

Oils from the tea?
posted by Cool Papa Bell at 10:44 AM on August 21, 2008

I'd guess oils from the tea, the iced tea maker, or maybe the pitcher. Oil tends to get reflective and shiny in a weird way, especially on top of darker liquids. Try putting some olive oil or chap stick on your lips, take a sip of tea, and see if you get the same result. It could also be some chemicals ambient in your water. Probably non-toxic, but you might want to get a filter, just for taste reasons, if that is getting through.

I'd say not to worry too much. What exactly is your "iced tea maker?" Is it a sun tea jar type thing?
posted by mccarty.tim at 10:47 AM on August 21, 2008

I've seen oil spots like this floating on iced tea at several different restaurants, so I think it probably is oil from the tea itself.
posted by pocams at 10:48 AM on August 21, 2008

Sometimes in tea, hot or cold, I get these floating solids - but they're thin, as thin as a little oil slick. I have always assumed it was a combination of tannins and minerals from the water. Is your water hard? Though I don't really know what they're actually made of either though I don't think it's oil as it will stick to the sides of the tea cup and seems to behave more like a solid than a liquid.
posted by GuyZero at 10:54 AM on August 21, 2008

Response by poster: It's a $20 mr. coffee iced tea maker similar to this.
posted by realpseudonym at 10:57 AM on August 21, 2008

@GuyZero: If they're unsaturated oils, they'll stay liquid, just be more viscous. They're probably floating to the top overnight, because when the tea is hot/just chilled, the liquid is still more or less an emulsion.
posted by mccarty.tim at 11:01 AM on August 21, 2008

that is a thin film (formed probably by some oils in the tea). the colors you see are the result of the interaction of light between the fluid below and the "thin film" itself (google around for "newtons rings" too)
posted by The_Auditor at 11:41 AM on August 21, 2008

It could also be leftover soap from the dishwasher.
posted by rhizome at 12:11 PM on August 21, 2008

If you squeeze fresh lemon into your tea, that could be the source of the oils.
posted by moonmilk at 1:08 PM on August 21, 2008 [1 favorite]

It's probably tannin.
posted by methylsalicylate at 2:02 PM on August 21, 2008

I wonder if this is similar to what I'd see when I used Lipton's one-serving bagged instant iced tea mix (with bottled water). It was more like little metallic-looking flakes and clumps than anything else.
posted by TheSecretDecoderRing at 10:54 PM on August 21, 2008

Tannin, probably: You see this (a metallic looking film or spots) on stewed tea, which is high is high in tannin. I drink tea black and I notice this with Indian tea if its brewed for any length of time, much less often with black China teas which are lower in tanin. Since Indian tea is usually drunk with milk which binds to the phenolic compounds (of which tannin is one) this is not normally so noticeable.

As an alternative explanation Howard McGee notes in 'On Food and Cooking':
"The addition of ice to normally brewed tea tends to make the tea cloudy, due to the formation of particles of a complex between caffeine and theaflavin. The way to avoid this is to brew the initial tea at room or refrigerator temperature over several hours.

If your ice tea maker uses hot brewed tea, it could be that these particles are rising to the surface when the tea is standing in the refrigerator overnight.
posted by tallus at 9:52 AM on August 22, 2008