I had the honor to join James, Chris Colby and Zot O’Conner in a Basic Brewing Radio show that discussed the results of a listener experiment on mash conversion time.

Triggered by Chris Colby’s comment that mashes convert in as little as 10-15 a listener experiment was conducted for which listeners had to record the progression of the iodine test and, if possible, the sweet wort extract content in the mash.

The result is what I have been observing on my own batches and in experiments: a negative iodine test (no starch or large dextrins present) is not necessarily an indication that the mash is done. Even after a negative iodine test the extract content in the sweet wort keeps increasing which is an indication that there is continued release of sugars and dextrins into the wort. If the wort would be lautered too early the efficiency into the kettle might suffer.

The experiment was also a good insight into how different brewers conduct the iodine test. Most are using the iodine solution in undiluted form which makes it difficult to tell if the color is coming from a reaction with starch or large dextrins or is coming from the iodine itself. I recommend diluting the iodine solution with rubbing alcohol (1 part iodine solution like iodophor, Lugol’s iodine or providone iodine and 9 parts rubbing alcohol).

Basic Brewing Radio: March 3, 2011 – BYO-BBR Conversion Experiment (iTunes|Streaming mp3)