Smoothies themselves don't inherently contain a specific type of acid. The type of acid present in a smoothie depends entirely on the ingredients used.

Here are some examples:

* Fruits: Many fruits contain citric acid (like oranges, lemons, limes), malic acid (like apples), and tartaric acid (like grapes).

* Yogurt: Contains lactic acid.

* Vinegar: Contains acetic acid (often used in green smoothies).

* Other ingredients: Some smoothie recipes might include ingredients like lemon juice, lime juice, or apple cider vinegar, which would introduce their respective acids.

So, to know what type of acid is in your smoothie, you'd need to look at the ingredients list!