# Gravity Weirdness

Howdy all,

So, over the last three brews I’ve had a strange experience where my first running gravity (1G) has been consistently quite low, but my target OG (using 80% efficiency to calculate) has been either on the money or significantly less off than 1G. In two cases, it was 10 points low after first runoff, but was 1 point over target OG going into the carboy. In the other case, it was 16 points low, but was only 5 points low going into the carboy. There seems to be a common thread here, i.e. that I have consistently regained ~10 points through sparging and boiling. Note that I did not take any action to get back on target…no extra boiling, no added extract, no nothing, I just let it play out.

Also, fwiw, in the case of the 1Gs that were off by 10 points, the final mash gravity (1st + sparge) was was only off by 6 - 7 points; for the 1G that were off by 16 points, I only regained 3 points after running in the sparge

What could possibly explain this? I’m very careful to stir up the wort each time I measure, I cap the sample and cool it to 60* each time, etc. Or, maybe I hold a misconception that points lost during conversion means original gravity will be impossible to hit?

Regarding conversion, here are things I’m confident are on point:
-Good grain crush (crush at home, virtually no intact husks left over)
-Good thermometer (traceable NIST certification)
-Dough in volume (use devices calibrated by weight, and use a scale to measure “odd” volumes, e.g., measure 4.5 gallons and weigh .2 gallons if 4.7 gallons is necessary).
-Target 1G (I simply calculate mash thickness and refer to Kai’s chart)

And, if it’s helpful, here is info on grain bill, water, and other notes about these brews:

1G off by ~10:
Grist:
9.5 lbs 2-row
.75 lb C60
.5 lb Chocolate Malt
.25 lb Victory

Strike and Sparge:
4.7 gal strike @ 172
4 gallon sparge @ 170
Mash thickness: 1.709
Mash in Target: 158 degrees
Mash in Temp: 156
Mash pH: 5.3
Mash out Temp: 15
Pre-boil Volume target: 6.94 gallons
Pre boil volume: ~7.5 gallons

Gravity:
1st Run Target: 1.072
1st run actual: 1.063 (87.5% conversion)
MG target: 1.046
MG: 1.040
OG target: 1.049
OG:1.050

===============================

Grist:
9.5 lbs 2-row
.75 lb C60
.5 lb Chocolate Malt
.25 lb Victory

Strike and Sparge:
4.7 gal strike @ 172
4 gallon sparge @ 170
Mash thickness: 1.709
Mash in Target: 156°
Mash in Temp: 155.8°
Mash pH: 5.2
Mash out Temp: 153°
Pre-boil Volume target: 6.94 gallons
Pre boil volume:

Gravity:
1st Run Target: 1.072
1st run: 1.062 (86% conversion)
MG target: 1.046
MG: 1.040
OG target: 1.049
OG: 1.050

==================================

1G off by ~14:
Grist:
12 lbs 2-row
.5 lb C-60
.5 lb Munich

Strike and Sparge:
5.00 gal strike @ 168
3.88 gallon sparge @ 170
Mash thickness: 1.54
Mash-in Target: 152
Mash in temp: 153
Mash pH: 5.3
Mash out temp:
Pre-boil Volume target: 6.94 gallons

Gravity:
1st Run Target: 1.080
1st run actual: 1.064 (80% conversion)
MG target: 1.055
MG actual: 1.042
OG target: 1.059
OG: 1.054

If I continue to see ~80% efficiency (OG) consistently, I’d love to stop taking gravity samples other than for OG and FG; however, I’m not comfortable doing so until I can fix conversion issues, understand how I’m “making up” for conversion losses and fix it, figure if/why my 1G gravity measurements are inaccurate, understand why I shouldn’t worry about any of this…etc…heh

Note that the brews above are not listed in order. The last one listed was brewed in between the other two, and its 73% efficiency is the lowest I’ve seen in awhile.

Why not take a sample and measure the gravity from inside the tun, itself? That is, before any wort is “run off”, scoop a bit of the mash into a glass and look at the gravity reading of that.

Assuming you’re not doing that already, that could theoretically identify whether or not it’s a conversion or lautering issue.

Well, I’m batch sparging, and I fully empty the tun before adding sparge water. I suppose it’s possible I’m leaving sugars behind when I drain? If I pull directly from the tun, I’m thinking I should stir it well first, pull the sample, let it resettle, vorlauf, and drain. Yes?

Unfortunately I’ve taken a 5 month break, and I can’t recall when I took my 1G samples (in tun or after draining) before the hiatus. My notes do indicate that I was hitting very close to 100% pretty consistently, though.

How are you deciding what your first runings gravity should be?

I calculate mash thickness, then consult Kai’s chart
http://braukaiser.com/wiki/index.php?title=Understanding_Efficiency#Measuring_conversion_efficiency

[quote=“ickyfoot”]I calculate mash thickness, then consult Kai’s chart
http://braukaiser.com/wiki/index.php?title=Understanding_Efficiency#Measuring_conversion_efficiency
[/quote]

That’s what I assumed. if your conversion efficiency is low, you must be making up for it with sparge efficiency.

Interesting. I guess I assumed conversion rate would be a pretty powerful constraint on sparge efficiency, i.e., if the starches simply aren’t broken down, then how can they be rinsed out and into the kettle?

Is it possible I’m just not letting the tun drain long enough before sparging? Might that explain it? Yesterday, after sparging, I closed the tun spigot, got the kettle on the burner, and then about an hour later, I opened the spigot again. I ended up with a full quart of additional wort. If I’m leaving a quart or more of collectible wort (as opposed to the un-collectible quart I lose below the spigot line) behind during first runnings, could that contain a full 10 points worth of sugar? It seems like it might explain how I’m recovering something during sparging, but is it enough to explain these discrepancies entirely?

Maybe…I guess you won’t know til you measure it. I’ve taken to slipping a 2x4 under my cooler to tilt it after the runoff stops. I get anywhere from a couple cups to a bit over a qt. of extra wort from that. You might try it and see what happens for you.

I don’t have access to my numbers right now, but I think it could be a sparge efficiency issue. I BIAB and dunk sparge. The great thing about BIAB is that you can squeeze the heck out of that grain bag and get a lot more extract out of your grains. Until you do this, you don’t realise just how much liquid is left in that grain bed. After squeezing I dump my used grain into the plastic bag from NB. If I let is sit and look at if after my brew day is done, I can still see liquid that has oozed out of the grain in the bottom of the bag.

P.S. I’ve yet to experiance any amount of tanin extraction that I can notice.

If anything, the sparge may have saved me. Still, that’s an interesting point about being able to squeeze the grains if going with BIAB…

I think I’ll try what Silentknyght suggested: once the mash is completed, I’ll stir it up, pull a sample directly from the tun, then drain.

Denny, I already use a 2x4, and sometimes I even tilt it waaaay up towards the end (although when I first built the tun, I tested this and it probably ran off no more than a cup of liquid from the dead space). I just haven’t been letting it sit all that long before sparging. And, incidentally, I have been adding the additional quart to the boil when there is about a half hour left. If all of this is related to not fully draining the tun, then that would certainly explain why my numbers increasingly improve as I first rinse the grain and then add the additional run off during the boil.

If sampling the completed mash in the tun indicates 100% conversion (or reasonably close to it), then I think that would confirm that this is just a procedural problem. If so, then it’s unlikely I’m not gonna change anything. I might wait an extra 5 - 10 minutes before sparging, but since I’m not mashing out I’m somewhat anxious to get the kettle on the burner.

Looking at your OP, I see 170 listed for the sparge. Is that the water temp or the grain bed temp? If it’s the water temp, try 190F water and see if it helps.

Yeah, 170 is the water temp. Is the purpose of going to 190 to make the mash less viscous so it runs off more freely?

Is there a grain bed temp at which I have to worry about tannin extraction?

Yes when its hotter you’ll pull more sugars into solution. 190 will put you closer to 170 by the time you stir it into the grains. Dont be scared

Ha! Not scared, I just don’t want to make astringent/tannin-y beer

Hoping to brew this weekend…I’ll pull a sample both from the tun and from the kettle after first runnings, and then will sparge with water at 190 and see what’s what. I feel like I’m getting very close to dialing in my process…very excited to get to the point where I’m nitpicking over ingredients instead.

Thanks again all! :cheers:

[quote=“ickyfoot”]Yeah, 170 is the water temp. Is the purpose of going to 190 to make the mash less viscous so it runs off more freely?

Is there a grain bed temp at which I have to worry about tannin extraction?[/quote]

You want to get the grain bed to 170. It will help gelatinize and convert any remaining starches and likely increase your efficiency. It did with me.

Tannin extraction is pretty much dependent on pH, not temp. If your pH is OK, temp really doesn’t matter. That’s why you can do decoctions, where you boil the grain.

Kai Troester kinda disproved that with his room temp sparge experiment.

[quote=“Denny”]You want to get the grain bed to 170. It will help gelatinize and convert any remaining starches and likely increase your efficiency. It did with me.

Tannin extraction is pretty much dependent on pH, not temp. If your pH is OK, temp really doesn’t matter. That’s why you can do decoctions, where you boil the grain.[/quote]
OK, that’s what I thought re: gelatinization…

Good to know re: tannins and pH…