Low efficiency, undershot mash temp = overshot OG?

[Monkfish]

Hey guys,

I did my third AG this weekend (5 gallon clone of Pliny the Elder) - with my last AG batch I got 72% efficiency but this time around I ended up with 59% (using the same crush settings on my mill). My target mash temp was 151* - using Beersmith I used 18.3 qt of 165* strike water (and 14.4 qt of 168* sparge water.)

I preheated the MLT w/ 175* water for 20 minutes - then when mashing (165* strike water) in I stirred like a madman for a good 10 minutes - when I closed the lid of the cooler I was at 149* - after a couple more minutes it settled in at 147* for the duration of the mash, even with stirring every 15 minutes. Next time I'll definitely up the strike water temps a bit.

The grain bill was:
12.7 lbs. - 2 Row
9.3 oz - Crystal (40L)
9.3 oz - CaraPils
11.7 oz - Corn Sugar


My preboil gravity (temp corrected) was 1.050 before adding the corn sugar - after adding the sugar it rose to to 1.060. After a 90 minute boil I ended up with a gravity reading of 1.075. The recipe called for an OG of 1.070, Beersmith predicted 1.069.

My efficiency was way off - which led to a low preboil gravity reading. But my mash temp was way low (4* off - M.A.L.T)...did these two factors offset each other to some extent and end up resulting in my overshooting of the OG?

Does the above assumption sound plausible or could there be something else in play?

Thanks in advance,
MF

 

[Double_D]

It could be your wort wasn't mixed well and you took a sample off the top where the less dense liquid would be.

 

[jetmac]

What was the volume of wort pre-boil and post-boil. You should have kept an eye on this.

You could have figured how much to boil off to achieve your desired gravity. It sounds like you boiled off too much wort. You can still boil for 90 min, you just have to boil less agressively. You may also need to have a larger volume of wort pre-boil. Something you may not have considered.

And I would like to point out, when you stir your mash it will help lower the temperature. So stiring like a madman for 10 min and stiring every 15 min kept lowering the temperature. Next time try stiring enough to mix well and get rid of dough balls, then close the lid and cover with a blanket. Check it again if you want after 20 or 30 min but I would suggest to only stir to get the temp down.(this is assuming you used a cooler for a mash tun)

 

[Jayhem]

I'm not sure what caused the higher OG but I have learned on my first 3 AG batches that I have to have strike water in the 170-175F range in order to start the mash at 155F. I find that with my equipment if I start the mash at 155F then it will finish around 150F since you loose heat constantly, especially when you open the lid to stir.

 

[Monkfish]

What was the volume of wort pre-boil and post-boil. You should have kept an eye on this.

Pre-boil (pre dextrose) I was at 6.1 gallons. 4.75 gallons went to the carboy after a 90 minute gently rolling boil (still figuring out boil off/wort chiller loss rates and hop spider displacements)

Thanks

 

[jetmac]

Pre-boil (pre dextrose) I was at 6.1 gallons. 4.75 gallons went to the carboy after a 90 minute gently rolling boil (still figuring out boil off/wort chiller loss rates and hop spider displacements)

Thanks

After some calculations the numbers you have corolate. My suggestion is you didn't have enough wort in your kettle pre-boil.

If you added enough water to bring wort volume to 7 gallons that would have given you a gravity of almost 1.052. you could then boil that down to 5.25 gallons resulting in a post-boil gravity of 1.069.

 

[dcp27]

My efficiency was way off - which led to a low preboil gravity reading. But my mash temp was way low (4* off - M.A.L.T)...did these two factors offset each other to some extent and end up resulting in my overshooting of the OG?

Does the above assumption sound plausible or could there be something else in play?

No. mash temp isn't related to efficiency (unless you didnt rest til full conversion)

what temp was your pre-boil gravity reading taken at?

 

[Monkfish]

No. mash temp isn't related to efficiency (unless you didnt rest til full conversion)

what temp was your pre-boil gravity reading taken at?

Hmmm...pre-boil gravity was taken at 65* (I cooled a sample of wort) and temp corrected.

 

[dcp27]

it probably just wasn't well mixed then, which is kinda evident by your 2nd pre-boil reading. 11.7oz of sugar couldn't possibly bring it up 10pts.

btw, not sure about your calculations, im getting 64% efficiency

 

[Monkfish]

it probably just wasn't well mixed then, which is kinda evident by your 2nd pre-boil reading. 11.7oz of sugar couldn't possibly bring it up 10pts.

btw, not sure about your calculations, im getting 66% efficiency

That would definitely make sense. I did skim off the top of the brewkettle and didn't mix thoroughly before taking the sample (and I did stir in very well when incorporating the sugar.)

When measuring efficiency using preboil, should I be using the preboil wort with or without the sugar (which I added to the brewkettle after sparging?)
I assumed the former - but that was an assumption (since the sugar didn't need converting.)

Thanks again

 

[dcp27]

im not sure how the different software/calculators actually factor the sugar into the efficiency calculations (I just calculate it myself). it may depend if you check post-boil add or not.