As I've mentioned in a previous post, I like the acidity that lemon brings to iced tea, but I don't want my iced tea to taste like lemon—I want it to taste like tea. Therefore, I decided to run some trials adding different amounts of various pure acids, to try to achieve a neutral acidity that would complement the tea flavor.
For the first test, I tried malic acid (powder), lactic acid (88% solution), and acid phosphate (a solution containing phosphoric acid partially neutralized by phosphate salts). Malic acid is found naturally in fruit like grapes and (especially) apples. Lactic acid is mainly found in substances that have undergone lactic fermentation, such as yogurt, sauerkraut, sour beer, and some wines and ciders. Acid phosphate was once used at many soda fountains, and has recently made a minor resurgence in the world of craft sodas and cocktails. In the future I will also try citric acid (found in citrus fruits) and straight phosphoric acid (often added to modern sodas).
Since the malic and lactic acids I used are very concentrated, I had to be precise with my measurements. After undershooting and then overshooting my desired level of acidity, I settled on a ratio of 1.3 grams of malic acid or 4.2 ml of lactic acid per liter of tea. I did not much like the taste of the acid phosphate with the tea, so I didn't try very hard to dial it in.
I found that, at similar levels of perceived acidity, lactic acid enhanced the tannic astringency of the tea, while malic acid did not. I therefore preferred the tea with malic acid. I also found that tea acidified with malic acid makes a very nice lightly sweetened tea with (the equivalent of) 3 teaspoons of sugar per liter of tea. And I don't usually like sweet tea!
If anyone wants to give this a try, I'd love to get another opinion. The malic acid was $12 for a pound, and I very much doubt I will ever use all of it.
Note: I do not recommend adding acids to iced coffee. It's weird.