There are a couple of reasons I suggest we use tartaric or citric in the pages of The Winemaker’s Answer Book for cleaning and sanitizing purposes. First of all, acid is added to sulfite solution to increase the effectiveness of the sulfite by lowering the solution’s pH. The first, and most practical, reason for adding citric or tartaric acid is that food-grade acid blend (sold for adjusting the acidity of musts and juices) tends to be more expensive and sold in smaller packets than straight up citric or tartaric acid (which often can be had at a bulk discount in larger bags).
The second and perhaps the most important reason is that if you’re doing your final rinsing with an acid blend that contains malic acid, you’re potentially releasing a food source for various bacteria into your equipment and into your cellar’s environment (like drains). Even if you rinse well with water afterwards, you are still needlessly introducing energy sources for bacteria into your winemaking environment. Call me paranoid, but I would never unnecessarily put yeast or bacteria food out where some of the “bad guys” might get it. For instance, I would never use an acid blend for a “wet storage” solution (acidified sulfur dioxide solution) for a barrel.