Starch Test

The whole point of the mash is to convert all of the starch in the grain into sugars.   At certain temperatures, enzymes within the grain kernels will act upon all the starch (endosperm) and convert them to sugars.  Brewers need these sugars to provide food for the yeast.

One easy test to determine when starch conversion is complete is to add a few drops of iodine to the wort.  Basically, I draw off a small amount of wort onto a white plate and put a few drops of common tincture of iodine (the stuff old guys' moms used to put on their cuts and scrapes.)  In the presence of starch, the iodine will turn a dark blue.  In the absence of starch, the iodine will stay a rust color.

Most American malts are so highly modified that conversion usually takes place in about 10-15 minutes.

I don't often do iodine tests in the Brewery because the efficiency of our equipment is very good.  However, I like to do it at home for peace of mind.  Here is the result of my iodine test:

No blue at all.  Time to sparge.