I was playing around with step mashing to get slightly better efficiency in my biab batch and for better control of the beer body. I am very new to home brewing and this was probably too much too soon. In addition I still haven't determined my efficiency to know what my target OG would actually be.

I started mashing at 148°F. The plan was to mash for 20 minutes at this temperature but my specific gravity seemed really low so I let it go another 20 minutes before raising the temp to 155°F, where I planned to mash for 15 minutes, but again my SG was off so I doubled that time too. I was expecting my efficiency to be higher than estimated and did get about 0.015 points higher than my recipe OG.

This was a mistake since I needed to calculate my efficiency for this new process. I should have just done a single extraction step at a single temperature that would have had more predictable results. I will do that next and use idoine to see if conversion is complete but I was wondering if I could learn anything from this process and if it was a good idea to determine my mash time based on my SG readings?

4 Answers 4


Short answer for your question is no. But I don't really understand what you were measuring during the mash steps. Mash is usually thick until you do a sparge to get the most solids out of your grain. You usually measure your SG after the sparge (pre-boil SG).

Until you know your equipment effectiveness more accurately, this is just about hitting approximate values. But you can easily correct your SG before boiling by just adding water (to lower SG) or boiling out more water (with longer boil time or adding heat power to raise SG). There are some calculators to measure the amount of water needed for this, just search for 'Dilution And Boiloff Gravity Calculator'.

As for the refractometer measurements during the mash steps - don't do that. They are much useless during that period. Just take them after sparge and correct SG if required as noted above.

If you need to know if your conversion is actually complete there is a simple solution for this - iodine test. Just get a iodine tincture (alcohol iodine solution), take a liquid part (without solids of grain) of your wort from the mash and add a tiny drop of iodine. If conversion are done it shouldn't change it's color. If it turns blue of violet this means starch is still present and you must continue with conversion. If it doesn't changes it's color that means the conversion are complete (though some processes still goes on affection your FG/body, that is why mashout is recommended, to stop those). Also if it's red that means the conversion is nearly complete, starch is absent but some of the long dextrins are still in place which is might be actually good for a very full bodied beers. Iodine test is much more accurate if you really want to know if your starch conversion are done.

  • My question was poorly asked and i left out that this is boil in a bag with full volume of water. I didn't think to have iodine. I had too many new things going on. Hopefully post video soon some of what i was doing might make more sense. You answered all the questions i had even the one i was trying to get to when thou mentioned red iodone and dextrins Sep 5, 2017 at 6:27
  • Ah, so you are doing BIAB. Then yes, your SG will rise with time. But that is not because of the conversion, that is because you are actually "sparging" all the time during the process :) As for iodine tincture I saw some are sold on the Amazon. I don't know your location and how it goes in other countries (I'm outside of the US) but in my place these are sold for less than $1 in any pharmacy store without any prescription.
    – NStorm
    Sep 5, 2017 at 6:32

Tbh I'm not sure what the question is.

Palmer in one of Brew Strong podcasts says that approx 80% of all conversion occurs within the first 20 minutes or so. Longer mash time is required to finish conversion of remaining "long tail". Brulosophy's Marshall Schott also says you can cut total mash time from 60 to 45 minutes without much impact on the taste and gravity.

The modern malts most likely don't require all that step mash black magic. I used to do step mashes, overnight mashes, even a decoction once or twice, but when I switched to single infusions, I didn't see any difference in efficiency, fermentability or taste.

I guess the point of this ramble is.. What I'd do (and, in fact, did). Do 1 hour single infusion mash at 148, then short mashout at 175, measure your system's efficiency, record that parameter in Beersmith (or whatever brewing software you use) and stop worrying about it. That will free up thinking resources to worry about really important stuff like yeast health and water chemistry.

  • 2
    Indeed, depending on the malt you use, a step mash may actually be detrimental...depending on the steps. But in general, maltsters have taken care of anything that you used to gain from a step mash.
    – Denny Conn
    Sep 3, 2017 at 16:59
  • I guess I should have simplified this question like I should have simplified my brew day :) There's a reason why I did it that way but basically. Assume I just had one mash step at 153 degrees for 60 minutes. If I take refractometer readings is that enough to know when conversion is complete or does SG still go up for other reasons? Sep 5, 2017 at 4:25

Conversion of starches to sugar is only part of the issue. The iodine test will tell you when the starches are gone, but it won't tell you which sugars are in the solution. A longer mash will allow the longer sugars to be broken down into shorter ones. That may not affect SG but it will affect fermentability. Since a refractometer is adjusted to read simple sugars, it may respond to that change, but a hydrometer would not.

I have found that patience is rewarded when making beer, and I am trying to simplify my process. I no longer use an iodine test and just let it sit for an hour at my desired temperature.


Yes it's normal for the SG to rise during a step mash. But will no longer rise once conversion is complete (check with iodine test)

While you can monitor the SG during the mash and it is a useful measurement, it's difficult to be accurate. It really needs to be a recirculating mash (RIS) so it's evenly mixed. Also sparge volumes need to be added in as dilution. Full volume BIAB won't have this issue, but usually you won't have RIS in a simple system. Many will say the uncovered starches skew the readings in refracto meters and even buoyancy tests. While technically a sound caution, it's not what I've experienced and my readings via refractometer are pretty close if you can capture clean wort. Mainly because the starches are not disolved and mostly hang out in the endosperm until converters to sugar and dissolved.

  • As odd as it may seem this was a full volume biab, no sparge recirculating mash. Sep 22, 2017 at 22:23
  • @OrganicLawnDIY if the mash isn't evenly mixed by RIS, then you really don't know if the reading is a true average. Even reading after a sparge wort should be well mixed before. Sep 23, 2017 at 5:30

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