Why Does Iced Tea Get Cloudy?

The leaf of the Camellia sinensis plant—the shrub that tea comes from—is complex and contains many different chemical components, which dissolve in water when tea is brewed. When some of these components meet each other, they bond together and form larger aggregates, and those precipitate out of the solution when the tea gets cold, turning iced tea cloudy. 

The soluble compounds in tea include amino acids, minerals such as calcium, sugars, volatile aroma compounds, and an enormous array of different polyphenols, large molecules that contribute to the color, flavor, astringency, and claimed health benefits of tea.

Brewing tea extracts those compounds into the water, but that’s not the end of the story. 

Once extracted, they transform and combine in various ways. For instance, calcium in the brew causes polyphenols to bind with each other, with amino acids, and with caffeine, to form larger aggregates. In hot tea, those aggregates are dissolved and invisible; but as the tea gets cold, the cooler water can no longer keep all those aggregated complexes dissolved, so some of them come out of solution and turn into visible haze in the tea.

The haze-forming potential depends on the particularities of the tea: how it’s grown and how it’s processed. Black tea and green tea are both subject to haze. Shade-grown tea leaves have a lower polyphenol content, so they are less haze-prone than other tea leaves, all else being equal. And tea leaves that are advertised for making iced tea are generally selected and/or treated to limit haze.

There are a couple of very easy ways to de-cloud iced tea that has become cloudy, but they have downsides.

1. Warm it up slightly. Doing so will cause the polyphenol complexes to re-dissolve and the tea to clarify. But the tea won’t be icy cold any more. And it will cloud right up again when it gets cold again.
2. Dilute it with ice water. This allows the complexes to dissolve in the additional water. But the tea will be weaker.

There’s also a less easy approach of clarifying the brew by stripping out all those hazy particles, which can be done with the same sort of methods used for clarifying wine and beer. However, that also strips out a significant amount of color and flavor from the tea.

Since all of these methods have disadvantages, the best thing is to prevent the formation of haze in the first place.

The tea industry has been studying the problem (which they refer to as “tea creaming”) for decades. There are a number of technological solutions that are beyond the resources of the home cook, but I tested out several possible prevention methods. For each sample, I used Lipton Yellow Label loose black tea, in a ratio of 6 grams (1 tablespoon) to 1 cup of water, brewed at 190 degrees for 4 minutes. This ratio makes a fairly strong iced tea—which I happen to love, and which also guaranteed that all my control samples would be reliably cloudy when chilled.

Methods That Failed

1. Rapid chilling of the tea after it’s brewed has been claimed to help prevent haze, but immediately stirring the hot brewed tea with ice was not effective.
2. Extra-slow chilling has also been mentioned as a remedy, so I tried putting hot brewed tea in a insulated vacuum container so that it took 12 hours to cool down to 45 degrees. The haze was unaffected.
3. Distilled water for brewing contains no dissolved calcium, so it might limit the formation of polyphenol complexes. But there’s more than enough calcium in the tea leaves already, so the calcium content of the water did not make a difference.
4. Precooking the tea leaves, which is mentioned in some studies, either by roasting or steaming, was not effective.
5. Adding sugar to the tea while it brews did not make a difference. There’s good evidence that adding sugar to tea leaves before they’re dried and aged is effective, because it sequesters some of the polyphenols, but that’s not an option for us.

One Less-Practical Method That Worked

Chelation is a chemical means of bonding metal ions in a liquid. Calcium is a metal ion, so locking it away with a chelating agent seemed like a plausible approach. Indeed, EDTA, a powerful chelator, did prevent haze formation. But it’s not a household ingredient. Commonly available citric acid is also able to chelate calcium, to a lesser extent; unfortunately, not enough to help with iced tea.

1. Cold-brewing tea is extremely effective. Steeping the leaves overnight in room-temperature water (or water as warm as 110 degrees) made a flavorful brew that was immune to haze formation, even when it was boiled and rechilled. It just needs to steep longer than a hot-water brew to extract the proper flavor. 
2. Starting with a lower brewing ratio also works very well.  In my testing, six grams of tea (one tablespoon loose leaves) per cup hazed up; 2 grams of tea (one teaspoon) per cup (which happens to be Cook’s Illustrated’s recommended ratio) remained crystal clear. Four grams of tea per cup was only very slightly cloudy. Different brands of tea will vary significantly; regardless, you can always add more ice water at the end to clarify your tea.