Extending my mash rest past 60 mins seems to be increasing my gravity

Brewing Processes
1

I had read somewhere that most of an AG starch conversion happens in the first 20 minutes of the saccharification rest. That doesn’t seem to be the case for me today. I’m 115+ minutes into my saccharification rest at 153F and the gravity is still climbing. I did a mash rest for 15 mins @120F (protein), 15 mins @140F,  60 mins @153F and noticed my gravity was super low - 1.045 (wanting 1.056).

I did an iodine test with 10 minutes left (in the 60 min rest) and had some black stuff settle out but it was all brown at the 60 minute mark so thought everything was converted. This is the first time I’ve tried this.

I decided to let it rest another 15 mins and the gravity went up to 1.048. Hrm… Let it rest again for another 15 mins and the gravity went up to 1.052. Ok so things appear done via Iodine, but they must not be. I’m getting closer to my target so I let it rest to 100 mins and gravity went to 1.055. I’m using a refractometer and letting the sample cool down before checking. Even checked it five minutes later thinking maybe the temp was throwing things off but it comes up the same.

After 115 mins @153 I’m up to 1.057.

I’m using an Anvil Foundry with the recirc pump and brewing in a bag. Is this typical of a mash rest? I’m going to let it go another 15 mins and see where it ends up. I’m guessing it should flatten out at some point, but not exactly sure what’s going on.

update: After 130 minutes at 153 I’m up to 1.060. I didn’t really want an 8% beer but that seems to be where things are headed so turning temp up to 168F for mash out. I should probably post my grain bill in case it matters (using 8 gallons strike water for a no-sparge batch):

  • 12# pale 2row
  • 1/2# crystal 120
  • 1# Chit
  • 2 handfuls rice hulls
  • 1/2 tsp of Amylaze enzyme
2

I believe your enzyme addition may have influenced your results.  Getting all the gravity points from a mash is not the goal: brewing a good pint of beer is the goal.

A yr and a half ago, over a series of half a dozen + brews days, using the same ~12#  grist, milled at the same ~.040 gap, 1.75:1 water ratio, 5.5 gal strike, 3 gal batch sparge volumes, mineral additions, .162 pump flow setting, etc, I took samples at 20 minute intervals throughout the entire mash.

When graphed, the data from that series overlaid upon each other are nearly indistinguishable one from another. Very consistent results.

Over that series, I noticed most of the SG increase takes place within 20 min. @152*F. …but I measured additional SG increase to about the 100 min mark. Past the 100 min mark the SG did rise but very very little.

20 min 1.045, 5.47 pH, 65% of OG
40 min 1.056, 5.47 pH, + 11 points, 81% of OG (+16%)
60 min 1.060, 5.50 pH, + 4 points, 86% of OG (+5%)
80 min 1.065, 5.44 pH, + 5 points, 94% of OG (+8%)
90 min 1.069, 5.46 pH, + 4 points, (+6%)

But, I believe I also noticed something else: the resulting beers were “thinner”. This is purely anecdotal because I did not compare them side by side but I got that perception.

According to Palmer in How to Brew Chap 14: “A compromise of all factors yields the standard mash conditions for most homebrewers: a mash ratio of about 1.5 quarts of water per pound grain, pH of 5.3, temperature of 150-155°F and a time of about one hour. These conditions yield a wort with a nice maltiness and good fermentability.”

I have since moved back to one hour because I want more viscosity. It’s all just a balance of compromises.

3

Ah, Ok. So the 60 minute mash results are a middle-of-the road type of estimation. Glad to see you graphed similar results.  I’ll have to post back wheather the beer seems thinner but yeah that’s going to be a subjective measurement but I guess at some point, we’re brewing for our tastes but this is helpful information, thanks.

4

[emoji106]. I look forward to seeing what you think about the beer. It might be just what you’re looking for.

5

Simple answer is that your malt did not fully gelatinize with your mash process.
Gelatinization is what drives gravity, not conversion. The gravity of a 10% amylose solution is about the same as a 10% glucose solution.
Enzymes or lack of them is not your problem.

My best guess for your issue is that your thermometer is not well calibrated and 153F was about 144-146F.

Another option, if temp is OK, is channeling due to doughballs. Dextrins get trapped within the balls and get slowly released.

Happy new year!

6

…but I used three thermometers over my series: a Thermopen, a Chef’s Alarm, and a Pollard (?). All three agreed.  This led me to believe my temp data was spot on.  The SG results were consistent across time data points across the series.

7

Then doughballs is most likely your issue.

Less likely but theoretically possible is that the malt was severely unmodified, and dextrins were trapped.

8

I used the same Rahr Standard 2-row Pale malt from the same sack for five of the six brews (highly modified). But even when I changed sacks I got the same result.

I haven’t had dough balls since I began underletting my mash several yrs ago.

9

Definitely. It’s long been known that you can obtain much of the gravity and virtually all the starch conversion in something like 15 minutes of mashing. But extending the mashing period does extract a bit more from the grist and the enzymes continue to break the long-chain dextrin and sugars into shorter and shorter sugars. That does result in less mouthfeel and body in the resulting beer.

As mentioned, most things in brewing are compromises.

10

Which is the reason I mash pils and tripel at 148F for 90-120 minutes

11

Thinness from extending the mash just makes common sense - the Germans call it digestibility, I think.  The longer the mash time (especially in the zone where both alpha and beta work) the more the fermentability of the wort.  I am practicing on Leichtbiers lately and find that a 75-90 minute mash at 148F, followed by mash out gets me a pretty good sweet spot in terms of extraction, fermentability and body in the final beer.  I use 7 lbs of pils (or a pils/pale mixture) with .25 lbs acidulated malt.  Foundry system, single initial infusion (i.e., not recirc) of 6.5 gallons of treated RO (1g Brewtan B, 3 g CaCl2 and 3 g CaSO4) and 1 gallon batch sparge.

For what that is all worth - just thought the OP might be interested, given his observations.

12

The Belgians refer to is as digesibility.  Dunno about Germans.

13

How’s your crush?  A poor crush requires an extended mash.

14

Hey, I was going to say that!

15

The iodine test isn’t all that useful in mashing. The two types of starches in malt are amylose and amylopectin. The iodine mainly binds to amylose, less so to amylopectin. A negative result (brownish-orange color) means that the amylose has finished converting but it doesn’t tell you anything about whether the amylopectin has.

16

I wish I could make a knowledgeable comment on it but I just haven’t seen enough grist to say either way.  I rely on my LHBS to do the best they can with it. There wasn’t a lot of flour at the bottom of the bucket after mashing in if that’s any indicator. If I was to collect it all, it might have been a half cup.

17

Always good to hear how others are brewing on their Foundry.  The more I read about brewing, the more it seems that every “rule” is really just a knob to turn. Appreciate it, thanks!

18

Well said.

19

That would explain why the iodine was done around the 60 minute mark, but my sugar content was still going up 30 minutes later. This whole brewing thing is really like 30% about beer and 70% about the science behind it =J

20

The crush is the problem then. I have spoken. ;)  And I am serious, I think this is it.