Is Sun Tea a Good Idea?

I just saw yet another recipe for sun tea—made by putting tea leaves or tea bags into a container full of cold water and then letting the thing sit in the sun for a few hours to brew. But sun tea is a terrible idea!

sun tea
Steeping tea with the sun’s heat

And although this particular article (Carr 6/1/20) claims that bacterial fears shouldn’t be an issue as long as you use “distilled or filtered water,” sun tea is still a terrible idea!

Or is it?

Here’s a quick look at the controversy.

The Problems

There are several issues: the choice of water, the source of the potentially dangerous microbes, the brewing temperature, and storage time.

First off, the water itself is probably irrelevant. Whether distilled or from the tap, the water has little to do with the safety of sun tea, assuming your tap water has met safety standards (not always a given, as we’re discovered yet again in the past few years).

To all accounts, the source of microbes is from the tea itself, and that can occur in multiple ways.

Ceylon 430 lvs
Ceylon OP Nuwara Eliya leaves

Since tea leaves aren’t washed before they’re processed, whatever’s on the leaves before they are picked remains on the leaves—along with anything found on the harvesting equipment, whether a person’s hands or machinery.

As the leaves are transported to the processing facility, the top layer of leaves is often exposed to airborne contaminants while the bottom layer is exposed to whatever is in the transportation container. At the facility, however, the heat used to stop oxidation and to dry the tea will get rid of a lot of those microbes—but then the tea undergoes sorting and packaging, additional avenues for fresh contamination.

The tea leaves that ultimately make it into your house potentially may carry aerobic bacteria, spore-forming bacteria, yeast, mold, coliform bacteria, and the foodborne pathogens Bacillus cereus and Staphylococcus aureus (Gurtler et al. 2014).

Makes you look at those beautiful leaves a bit differently, no?

But as we know, heat again comes into play, killing anything nasty, assuming a high enough brewing temperature. In 1996, the CDC published the “Memo on Bacterial Contamination of Iced Tea,”* which warned against brewing tea at too low a temperature, brewing in a contaminated container, or storing iced tea for too long.

Brewing the leaves double strength, with water that had been boiling

The memo cites the “tea industry” as recommending brewing tea for iced tea at 195°F (thus, a black tea) in a clean vessel and then storing it for fewer than 8 hours.

Yet, although the potential for illness is there, the reality is somewhat less clear. The CDC memo, according to Gurtler et al. (2014:338), says that:

the concern over possible inadequate brewing temperatures in the making of sun tea . . . was mentioned, although there has never been any documented foodborne illnesses associated with sun tea consumption.

Soooo, sun tea is safe?

Well, the lack of reported cases of illness doesn’t necessarily mean there’s no risk.

According to Nanobugs Inc., a Lincoln-based educational microbiology and infection prevention program, it’s easy for microbes to grow while the tea is sitting in the sun—”especially those teas that do not contain caffeine”—because sunlight will not heat the tea to a safe temperature. In fact, they say that:

When added to water, these microbes can be revived and start multiplying—especially if they sit in warmer temperatures of 40 to 140 degrees. (Lincoln Journal Star 7/12/16)

And the sun will heat the tea only to around 130°F, well within the window of microbial danger.

The Role of Caffeine

And if you’re adding herbals such as mint to the tea leaves, or are sun-brewing solely with caffeine-free herbals? The danger can potentially be even greater.

Straining out the leaves while pouring the hot tea into ice cubes to make a quick iced tea

As with tea leaves, both fresh and dried herbs have multiple sources of contamination. Gurtler et al. (2014:339) state that “the presence of human pathogenic bacteria in dried herbs is well documented and a potential risk is evident.”

Since caffeine deters the growth of some strains of bacteria, there have been studies that focus on caffeine’s antimicrobial ability, especially critical since many bacteria are growing increasingly resistant to antibiotics.

Soooo, as long as I use regular tea I’m okay?

Well, as long as the tea’s not sitting around in the sun for too long since caffeine’s impact on bacteria doesn’t last indefinitely.

In the End

Aside from all the precautions, there’s also the taste factor. Sun tea will never taste as good as properly brewed tea, according to me anyway! I find that sun tea is sort of murky tasting, whereas a good brewed iced tea will be clean and crisp in flavor. But I get it that some people love sun tea, especially when it’s become part of summer tradition.

brewed tea
Iced Ceylon, brewed inside my house

But do keep in mind these guidelines: Brew your tea in something clean, don’t depend upon sunlight to get the brewing temperature to a safe level, and don’t let your brewed tea sit out for too long.

And note that these guidelines don’t apply only to sun tea. The CDC has found hazardous microbes in iced tea served in restaurants (Gurtler et al. 2014:338).

Sun Tea Safety Bring Up Additional Thoughts

Soooo, would the risk with sun tea be more pronounced for people with underlying health problems, similar to that with unpasteurized apple cider?

And, this makes me wonder about all the times that I’ve left brewed tea leaves sitting at room temperature for hours before I re-brew them. What is the minimum amount of time that tea leaves would have to make contact with hot water to kill bacteria? Are 1-minute brews sufficient? But then, how can those 10-second brews be enough?

And what about gyokuro, for example? Mine has a recommended brewing temperature of 140°F, right on the upper limit of safety. In Per Oscar Brekell’s The Book of Japanese Tea, he recommends 120°F, which is well within the danger zone.

Luckily for me I tend not to overly think such scenarios (I evoke the 3-second rule even though there is no such thing and I’m not particularly worried about storing food in a cooler during a picnic, for example).

I try to buy tea from reputable sources. After that, I’m reconciled to living dangerously with my tea! Except sun tea. But that’s probably because I don’t like it.

iced tea outside
Enjoying a glass of ice tea in the sun seems a safer bet than making tea with the sun!

*I’ve been unable to locate the original version of this memo. Many sources cite it, yet I couldn’t find it on the CDC website.
–Carr, Stevie, “Makeshift drink Monday: sweet sun tea,” Argonaut, University of Idaho, 6/1/2020.
–Gurtler, Joshua B., et al., ed., The Microbiological Safety of Low Water Activity Foods and Spices, New York: Springer-Verlag, 2014.
–”Nanobugs might be hiding in your sun tea,” Lincoln Journal Star, 7/12/2016.

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