This article is from the WineMaking FAQ, by malak@CAM.ORG (Don Buchan) with numerous contributions by others.
After a while, it is quite possible that your glass carboys in
particular, your plastic containers and other pieces of equipment have
a light, white coating. This is typically scale. While completely
harmless in and of itself to your wine, what it can do is harbour dirt
and/or spoilage organisms that may be hard to remove by usual rinsing
and cleaning techniques, including the use of chlorine bleach.
To get rid of this, you can do any of the following:
A) Use vinegar. This may only be partially effective as your wine is
already an acidic environment, and you may need to use a lot of vinegar
for it to be effective.
B) Ask your supplier for a food grade phosphate based cleaner
specifically designed for this, and let it sit in your container for a
few days, then rinse it thoroughly several times before putting wine in
C) Go to a hardware store and get some tri-sodium phospate. Use
according to the instructions and let soak for a few days.
D) Put some small pebbles or white sand sold for aquaria along with soap
and shake it vigourously.