Gravity Problems with Partial Mash

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Gravity Problems with Partial Mash

Postby pcharles » Sun Apr 22, 2007 10:04 am

Hi All:

I developed the recipe listed below using Beertools and Ray Daniels book to be a Maple Syrup Old Ale. I mashed the grains with an initial temperature of 154
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Postby jeff » Sun Apr 22, 2007 11:49 am

I opened up your recipe, but I am not sure I follow your description of the problem. The recipe shows 1.081 as the predicted OG. What reading did you get when you brewed the recipe?
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Postby slothrob » Sun Apr 22, 2007 1:03 pm

Right, 1.081 predicted at 75% efficiency, not 120%.

By the way, when I do a partial mash, I measure the volume and take a gravity reading from my combined runoff. This gives me the total gravity contribution I'm going to actually get from my mash. I then calculate how much extract I need to hit my target gravity, and only add that amount. That technique guarantees that you'll hit your target gravity every time, as long as you get your final volume right.
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Postby pcharles » Sun Apr 22, 2007 10:31 pm

jeff wrote:I opened up your recipe, but I am not sure I follow your description of the problem. The recipe shows 1.081 as the predicted OG. What reading did you get when you brewed the recipe?


The predicted gravity is 1.081 WITH the maple syrup added, mine is 1.080 without the maple. It should be 1.068 without the maple, so if you turn off the maple syrups radio button you will see what it should be.
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Postby pcharles » Sun Apr 22, 2007 10:35 pm

slothrob wrote:Right, 1.081 predicted at 75% efficiency, not 120%.

By the way, when I do a partial mash, I measure the volume and take a gravity reading from my combined runoff. This gives me the total gravity contribution I'm going to actually get from my mash. I then calculate how much extract I need to hit my target gravity, and only add that amount. That technique guarantees that you'll hit your target gravity every time, as long as you get your final volume right.


I said to myself that I would test and adjust this time, after having this problem with the doppelbock, but did not. I forget why, but I was busy showing my brewing friend how much fun the sofware was.

Checking the gravity and then adjusting is a good way to hit the gravity, but I am trying to figure out why I over shot the gravity. Normally, I hear about people who are are below the gravity. How common is it for the run off to be much higher than you expect? What factors cause the run off to be higher than you expect, assuming you run off the target volume?
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Postby slothrob » Mon Apr 23, 2007 5:47 pm

Every brewer needs to determine the efficiency of their system. 75% is just a common efficiency.

Having said that, I doubt you're getting 120% efficiency. That means you need to double check that you are actually measuring your volume correctly, that your hydrometer is correct, and that the scale you're using to measure your grain and extract is correct.

The two biggest factors influencing efficiency, either up or down, are degree of crush and volume. If you are sparging a partial mash grain bill with enough water for a full volume boil, you're going to get high efficiencies, but may have a problem with tannins.
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Postby pcharles » Mon Apr 23, 2007 7:16 pm

slothrob wrote:Every brewer needs to determine the efficiency of their system. 75% is just a common efficiency.

The two biggest factors influencing efficiency, either up or down, are degree of crush and volume. If you are sparging a partial mash grain bill with enough water for a full volume boil, you're going to get high efficiencies, but may have a problem with tannins.


I agree there is no way I could be getting 120% because that implies I am creating sugars. The sparge was as follows: collect first runnings, close tap, add another 2 gallons of 160 water, stir and run off again. That is all. The gravity was checked with a refractometer prior to dilution (1.099), and then with a hydrometer after dilution. I just checked the hydrometer and it reads 1.000 in 60
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