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What changes the color to blue when water is used to clean containers that held elderberry juice I used for winemaking?

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Morgan Donahue — via e-mail asks,
Q

 I have been an amateur home winemaker for the past three years and use elderberries in most of the wine I make. My question is: What changes the color to blue when water is used to clean containers that held the juice of the elderberries? I am sure it must be a type of acid, but would like to know what it’s name is. I will be waiting for your answer; I have asked many people and they can’t give me an answer.

A
You’re right in assuming that it has something to do with acidity, but the answer you’re looking for is not exactly the presence of an acid but rather the absence of one. Fruit juices exist in the acidic realm of chemistry. They have a hydrogen ion content high enough to make the concentration of acid greater than that of water. Quick chemistry lesson: If something is acidic it is said to have a low pH and if something is not at all acidic (“basic”) it has a high pH. I know that sounds backwards, but play along. The middle point that all pH values rotate around is the pH of water, which is entirely neutral and measures a 7 on the pH scale. The pH scale ranges from 0 to 14. Acids have pH lower than 7 and bases (things like bleach or baking soda) have a pH higher than 7, with14 being the most basic something can get. Wines typically measure around 3.5 on the pH scale. The terms are relative, however. A wine of pH 3.9 is said
Response by Alison Crowe.