How to tell when your Mash is Complete
  • ThymThym
    Posts: 122,054

    Ever wondered how to tell when your mash is complete?

    Most recipes will simply give you a guideline for mash duration, 60 minute mash, 90 minute mash. Some give you multiple stages like protien rest and saccharifaction rest... but how do you know it's done it's thing?

    The length of time a mash conversion takes is dependant on a lot of factors, temperature being one of the most important. So a recipe that calls for a 60 minute mash at 155 deg F is based on the "normal" amount of time it takes for the Alpha and Beta Amalyse to do it's thing, converting starches in the grains into fermentable sugars. But in reality this is only a good guess as to how long the process will take.

    If you want a clear wort, with the highest efficiency mash given your equipmentm you need to know when the starch conversion has actually completed.

    A simple, cheap and very effective method for determining conversion completeness is the iodine starch test. Think way back to highschool and you will probably remember that iodine, in the presence of starch will turn black as night. Since many of us have idophor on the shelf for sanitization purposes, we actually have everything we need to perform an effective test for starch in the wort.

    To perform the test, take a few ml of wort out of your mash tun, I usually fill a shot glass about 1/4 full, then add a few drops of iodine and swirl. Try this about 5-10minutes into the mash, and you should see the mixture turn black/purple. This indicates the presence of starch in the solution. Try it again around the scheduled mashout. If it still turns black/purple then you haven't reached the end of the conversion - give it some more time. Eventually you will see that adding the iodine/idophor just makes the wort turn a little more brown. That indicated that conversion is complete and it's time to mash out at peak efficiency, without concern for any potential adverse effects.

    Of course this is a lot easier with lighter colored worts. If you are brewing a porter or stout you may try diluting your wort sample a bit to get a reading. a 50/50 mix of water to wort will still contain enough starch to give a good indication, and it should be light enough along the fringe to show. Of course it's less sensitive, but for home brewing purposes it should do the job (besides a little haze is less noticeable in the dark beers so you don't have as much to worry about.)

    Ensuring you have complete conversion will greatly improve final beer clarity and result in cleaner tasting beers.

    Happy Brewing!


    Feel free to post your experiences with this or other starch testing techniques here!

    The only thing between me and a train wreck is blind luck..... - Kenny