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Old 03-01-2013, 10:02 AM   #1
nucciocioccio
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Default Partial mash and malt extract potential (SG)

Hi all, I'm new here and new at homebrewing. Made my first batch in partial mash about two weeks ago (second total batch, first was an extract kit).
Made a bitter, i'm going to bottle tomorrow, seems good, but something strange happened when brewing, so here's my question.
This was the original recipe (in metric system, as I'm from Italy) for 23 L batch, 10 L boil, late extract addition, 75% efficiency:
2 Kg Maris Otter
0.5 Kg Cara-Pils
0.2 Crystal 105a
0.1 Chocolate Malt
1.5 Kg LME extra-light
0.35 kg DME light

Made my mash at 68° (154 F) without worrying about my efficiency as I planned to achieve the planned OG (1.054) adding the right amount of DME; so when I came out with an OG of 1.048 instead of 1.064, with an afficiency of 58%, I modified my recipe by adding more DME, calculated in an amount of 0.75 Kg, considering potential of my extract was 1.046 PPG.
Well, after boiling my wort, adding the extracts and diluting to 23 L I came out with an OG of 1.048, this meaning I should have added 1 kg of DME to reach 1.054.
Trying to figure out the cause of these difference, the only thing I came tois a lower SG than the one i figured (and indicated by most software).
Has anyone experienced something like this before, or have a guess about some other reason for my low OG?
Sorry for the long post and for possible mistakes in writing, and thank you in advance

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Old 03-01-2013, 02:57 PM   #2
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Did you adjust all of those gravity readings for temperature?

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Old 03-01-2013, 03:23 PM   #3
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Yes, temperature was right, 20° C. I even thought about en error in reading or calibration of my densimeter, but 8 points seems to much for me.

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Old 03-01-2013, 09:50 PM   #4
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How well did you stir everything up before taking that last measurement? It sounds like after the boil you added enough water to get to 23L, and what probably happened is that you didn't get everything mixed together evenly, which I can tell you from experience is difficult to do. The wort at the top, where you probably drew a sample, was lighter because it contained more water, while the wort at the bottom was thicker and undiluted. I'd say if you topped off with water, you're probably very close to what you were shooting for.

Another way to figure it out would be to calculate the sugars you've got, but I'm not quite sure on the volumes. Since its easier for me to convert weights/volumes rather than the gravity values, I'll adjust to non-metric. If the 10L boil was a full 10L (2.6gal) and had a gravity of 1.048, that should give you 125 gravity points. Adding 1.1kg of DME (2.4lb) would give you another 110 points, plus 1.5kg (3.3lb)of LME for another 125, giving you a total of 360. In a batch size of 23L (6gal) that should give you a final gravity of around 1.060. So either I'm mistaken in some of the calculations (quite possible) or your volumes, you should have a higher gravity than you measured, potentially coming back to the mixing problem posed in the first paragraph.

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Old 03-02-2013, 12:39 PM   #5
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Quote:
Originally Posted by erikpete18 View Post
How well did you stir everything up before taking that last measurement? It sounds like after the boil you added enough water to get to 23L, and what probably happened is that you didn't get everything mixed together evenly, which I can tell you from experience is difficult to do. The wort at the top, where you probably drew a sample, was lighter because it contained more water, while the wort at the bottom was thicker and undiluted. I'd say if you topped off with water, you're probably very close to what you were shooting for.

Another way to figure it out would be to calculate the sugars you've got, but I'm not quite sure on the volumes. Since its easier for me to convert weights/volumes rather than the gravity values, I'll adjust to non-metric. If the 10L boil was a full 10L (2.6gal) and had a gravity of 1.048, that should give you 125 gravity points. Adding 1.1kg of DME (2.4lb) would give you another 110 points, plus 1.5kg (3.3lb)of LME for another 125, giving you a total of 360. In a batch size of 23L (6gal) that should give you a final gravity of around 1.060. So either I'm mistaken in some of the calculations (quite possible) or your volumes, you should have a higher gravity than you measured, potentially coming back to the mixing problem posed in the first paragraph.
Seems possible. I didn't take an OG reading for the wort made with the extracts, wich I brieflyboiled separately, so yours could be a solution. Unfortunately I think I can't get an answer til next brewing session. I will certainly mesure the extract wort in order to obtain certainly correct values
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Old 03-03-2013, 11:18 AM   #6
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How long did you mash at 68C ?

Please tell me exactly what you did .

When and how did you add your DME ?

If you boiled your DME separately and added it to the Kettle near the end of the boil , then the O.G.

should be lower than expected due to the change in Volume .

You could have added your DME directly to the Kettle and let it boil for the last 15 minutes .

That's my understanding from what you wrote to "erikpete18" .

Hector

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Old 03-03-2013, 12:11 PM   #7
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Could be due to a poor crush of the grains also, as that will have direct impact on the amount of sugars extracted from the grain.

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Old 03-03-2013, 01:16 PM   #8
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I mashed for about 45 minutes, but I recalculated the extract amounts after checking the real og of the wort from the mash. So is an extract issue. I diluted my extract in about 3 liters of water, and put in the fermenter, then added the cooled wort and topped up to 23 liters. Boiled the extract with water for 10 minutes or so, separately from the wort.

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Old 03-03-2013, 09:04 PM   #9
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Quote:
Originally Posted by nucciocioccio View Post
I diluted my extract in about 3 liters of water, and put in the fermenter, then added the cooled wort and topped up to 23 liters.
As I said , that's exactly what made your O.G. lower than expected .

By adding 3 liters of DME solution and then topping up to 23 L , you are diluting your wort more than needed .

So , you should make a more concentrated wort separately from Extract .

In other words , you used less DME than you actually needed .

Hector
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Old 03-04-2013, 09:43 AM   #10
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Quote:
Originally Posted by hector View Post
As I said , that's exactly what made your O.G. lower than expected .

By adding 3 liters of DME solution and then topping up to 23 L , yo.u are diluting your wort more than needed .

So , you should make a more concentrated wort separately from Extract .

In other words , you used less DME than you actually needed .

Hector
That's exactly what happened. My question is: the amount of DME needed to achieve an OG of 1.054 was calculated basing on a potential SG of 1.046 ppg. Seems the real SG is lower than that.
In fact 10 liters OG 1.048, boiled for an hour with an evaporation of 3 L and 7 L of wort after boiling with OG 1.071, diluted with 16 L of wort made with 1.5 L LME and 0.75 kg of DME, gives a final OG of 1.054, considering 1.046 ppg for DME and 1.037 ppg for LME. Maybe the values ppg were lower
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