Nick Carr on June 5, 2020 0 Comments Any homebrewer who has done some all-grain batches knows that the mash is of vital importance to convert non-fermentable starches into sugars the yeast can use to make alcohol. This conversion often referred to as saccharification, takes place when water at a certain temperature activates enzymes in the malt, which then begin to break down longer chain sugars. But how long does this take? When is the mash fully converted? Most recipes use the standard timeframe of 60 minutes for full conversion. But, higher gravity worts can require a longer mash and some recipes don’t need a full 60 minutes to complete. Also, conversion time can be affected by mash thickness, malt makeup, etc. An Iodine test can tell you when full conversion has taken place. What You’ll Need A “test platform.” This platform can be white railroad or sidewalk chalk, a scrap piece of drywall, or a scrap piece of white paper/filter paper that doesn’t contain starch. Alternatively, a small white bowl (ramekin bowls work great); white plate; or even a clean white surface will also serve. Iodine (Lugol’s iodine or an iodine tincture are best) Iodine is available from any local drugstore or pharmacy. Chances are you already have some in your home as part of your first aid kit. If you don’t, I’d recommend buying the smallest bottle you can find with an eyedropper. Even the smallest bottle will last you years if its sole use is for this test. The test can be easier to read by diluting the iodine in water or ethanol. Use about ten parts water or ethanol to one part iodine. This lightens the iodine’s dark color to more of a base pale yellow and makes the color change more apparent. The Basic Test Make a shallow depression in the top of your mash and allow it to fill with wort (the idea here is to get liquid with no residual grain or husk particles in it) Take a drop of this clean wort and place it on your white “test platform” Add a drop of iodine to the wort. Watch for a quick dark color shift. Testing Tips Always add the iodine to the wort and not the other way around. Getting the wort first allows you the chance to pick out any larger husks or particles, which made it into your sample, before you add the iodine. This also gives the sample time to cool before the iodine is added. Use a piece of white chalk, scrap drywall, or non-starched white filter paper as your test platform if available. These surfaces will absorb the wort and iodine into a single point and make any color change easy to see. Also, because it’s absorbed, comparison to other tests is easy. A false positive is also less likely because of the absorption; husk or particle matter is left behind and can be more easily removed before adding the iodine. And really with this method all you need is a small point of wort, so you can just dip a sterilized sharp point of some kind (temperature probe, ice pick, etc.) into the wort and draw out a single bead of liquid. A small piece of the large sidewalk chalk stood on end works well, as does a thinly cut piece of drywall stood on edge, so that the chalky middle makes up your test platform. If you must use the alternative white bowl, plate, or counter surface be particularly careful about not including malt particles or husk in your sample. This can cause a false positive. Also, don’t clean up the test so you can compare it to other tests. Reading The Results Blue-black, purple, dark red color shift: Positive for presence of starch. Conversion is not complete. Pale amber to pale yellow color shift: Negative for presence of starch. Conversion is complete. *Note: If you have not diluted your iodine it will be harder to mark subtle color shifts. Basically, in undiluted iodine, no color shift (it stays that reddish-brown color) means there is no starch present. Avoiding A False Positive Some brewers complain about getting false positives when performing this test. Most of the time these false positives (continually getting the darker color shift no matter how long they let the mash go) are caused by either malt particles/husk in the sample or a hot sample. Be careful when taking the sample. Try to draw out only liquid, no residual material. However, it’s also possible to have minuscule grain particles, which can cause a slower darkening in the test. In a true positive the color shift will happen quickly. So, you can count even this slow change as a negative indication of the presence of starch. Conversion is likely complete. Always let your sample cool. This is why it’s better to add the iodine to the wort sample rather than the other way around. In most cases, the time between moving the sample to your test platform and adding the iodine is enough to cool it sufficiently, but it never hurts to wait just a few extra seconds before adding the iodine. Practice So You Understand What to Look For It helps to practice and get familiar with what the test is supposed to do. You can do this by running a test you know will come back positive, just a few minutes into your mash. Note the color change and how quickly the reaction happens. Then every 15 minutes do another test, noting the lightning color shift (blue-black to purple to red to amber) indicating continuing starch breakdown. The color will continue to grow lighter until it tests negative for starch with a color range of pale amber to yellow if using diluted iodine and no color change (remains reddish-brown) if using undiluted iodine. Should I Use This Test All The Time? It isn’t necessary to use this test every time you brew. If you are brewing a familiar recipe where you already have an idea of the time to full conversion there’s no need to run this test. But if you are at all unsure, run the test, it’s a quick assurance. The test has more importance when trying a new or higher gravity brew, or if you’ve changed anything within your mash. The test is a good touchstone. Be sure to record and keep any data for future reference. Some recipes fully convert in 30 to 45 minutes. The iodine test can help you nail down the exact amount of time needed, possibly shortening your brew day. No one can complain about that! The iodine test is just another tool in the brewer’s toolbox. Sure, you can probably get away without using it most of the time, but it does serve a purpose. There is little excuse to not use it to get a little extra information about your mash. It’s simple, inexpensive and doesn’t take long. It may just end up increasing your mash efficiency, cutting a little time out of your brew day, or saving a brew by helping you realize the mash you were about to end at 60 minutes needs a little longer, making your beer all the better.