Author Topic: BIAB and OG (yes another BIAB thread)  (Read 1738 times)

Offline flbrewer

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BIAB and OG (yes another BIAB thread)
« on: October 16, 2014, 12:03:31 AM »
Just wanted to clarify something on my first go this weekend....

When my mash is over, I should check gravity correct?

If it's low at this point I'd add DME? Is this even necessary if it's in the ballpark?

*Thanks to Erockrph for the offline help with this already!

Offline Stevie

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Re: BIAB and OG (yes another BIAB thread)
« Reply #1 on: October 16, 2014, 12:07:54 AM »
Yeah. This will help you figure out your extract. From here you can add dme, boil longer or shorter. Software will tell you what your preboil gravity should be. For my small batches, it is typically around 60% of my intended og. So a 1.050 beer should be around 1.030 preboil for me.

Offline flbrewer

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Re: BIAB and OG (yes another BIAB thread)
« Reply #2 on: October 16, 2014, 12:11:16 AM »
OK, so based on the recipe I should let the extract guide me as far as shorter & longer boil or adding DME? Any charts to help guide this?

As others have said before, I think this is a BIG test batch until I get it dialed in...

Offline Stevie

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BIAB and OG (yes another BIAB thread)
« Reply #3 on: October 16, 2014, 12:29:39 AM »
Yeah. If your preboil is a bit low, you can add some. You will need to do some math, but calculators may exist. DME is about 40 points per pound per gallon. So if your preboil volume is 2 gallons and you find your self 10 points low, add .5lb of DME.

2 x 10 / 40 = .5

Shorter/longer boil is more about experience. You need to know what your boil off is or what a little extra vigor will do for you. If you have a good grasp on that, you can use more math to figure out how much longer to boil.
« Last Edit: October 16, 2014, 12:37:51 AM by Steve in TX »

Offline erockrph

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Re: BIAB and OG (yes another BIAB thread)
« Reply #4 on: October 16, 2014, 05:44:40 AM »
If your preboil is way off, then that's where I prefer to add DME. If you're in the same ballpark, then you might as well wait it out until your boil is done. I'd rarely consider adding DME if I'm within 2-3 points on a small or average beer. In those cases I just make a note of it and try to adjust for it next time (usually by adding more base malt).

I'm of the school of thought that DME (like sugar and honey) is of extremely low risk for harboring contamination. I've added it in dry and cold on a few occasions with no ill effects. But if you're able to add it on the hot side, all the better.

Once your system is dialed in, if your gravities are off on a couple of batches, then its time to start looking into things that may be affecting your efficiency (such as your crush on your grains).
Eric B.

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Offline Bevilaquafoto

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Re: BIAB and OG (yes another BIAB thread)
« Reply #5 on: November 18, 2014, 06:16:27 PM »
I'm so glad this subject came up. I did my first 2.5 gallon all-grain batch yesterday, and took a reading after the mash. I may be over thinking this, but I ran into a couple of issues. First, at the end of my mash, the temp of the wort was down to 146 degrees. In the minute or so it took to get a sample and to read it, the temp had fallen to 120 degrees. I think I was in the ballpark of the recipe (pre-boil gravity in recipe was 1.050 and mine was 1.042 at 120 degrees), but what I could use some help with is what temperature is the wort supposed to be when you take the pre-boil reading? The reading will vary based on the temp, as the hotter the wort, the less dense it will be. I am still struggling a bit with hydrometer readings. Should I have just dunked the hydrometer directly in the brew pot instead of taking a sample out?
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Offline morticaixavier

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Re: BIAB and OG (yes another BIAB thread)
« Reply #6 on: November 18, 2014, 06:20:09 PM »
I'm so glad this subject came up. I did my first 2.5 gallon all-grain batch yesterday, and took a reading after the mash. I may be over thinking this, but I ran into a couple of issues. First, at the end of my mash, the temp of the wort was down to 146 degrees. In the minute or so it took to get a sample and to read it, the temp had fallen to 120 degrees. I think I was in the ballpark of the recipe (pre-boil gravity in recipe was 1.050 and mine was 1.042 at 120 degrees), but what I could use some help with is what temperature is the wort supposed to be when you take the pre-boil reading? The reading will vary based on the temp, as the hotter the wort, the less dense it will be. I am still struggling a bit with hydrometer readings. Should I have just dunked the hydrometer directly in the brew pot instead of taking a sample out?

I prefer to collect a sample in a small (8 floz) mason jar, seal it and pop it in the freezer to chill to close to the calibration temp for your hydrometer. The correction tables get less accurate farther from the calibration temp and if you let it chill uncovered continued evaporation can give you a higher than accurate reading.
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Offline Bevilaquafoto

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Re: BIAB and OG (yes another BIAB thread)
« Reply #7 on: November 18, 2014, 06:22:30 PM »
That makes a lot of sense. Thank you. I'll try that. I was going nuts trying to figure in the rapidly changing temps.
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Offline denny

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Re: BIAB and OG (yes another BIAB thread)
« Reply #8 on: November 18, 2014, 06:24:41 PM »
I prefer to collect a sample in a small (8 floz) mason jar, seal it and pop it in the freezer to chill to close to the calibration temp for your hydrometer. The correction tables get less accurate farther from the calibration temp and if you let it chill uncovered continued evaporation can give you a higher than accurate reading.

I put the sample into a metal cocktail shaker.  That gets swirled around in a bowl of ice water.  In less than 60 seconds I can go from boiling to 60F.
Life begins at 60.....1.060, that is!

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Offline morticaixavier

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Re: BIAB and OG (yes another BIAB thread)
« Reply #9 on: November 18, 2014, 06:36:41 PM »
I prefer to collect a sample in a small (8 floz) mason jar, seal it and pop it in the freezer to chill to close to the calibration temp for your hydrometer. The correction tables get less accurate farther from the calibration temp and if you let it chill uncovered continued evaporation can give you a higher than accurate reading.

I put the sample into a metal cocktail shaker.  That gets swirled around in a bowl of ice water.  In less than 60 seconds I can go from boiling to 60F.

or this.
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Offline pete b

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Re: BIAB and OG (yes another BIAB thread)
« Reply #10 on: November 18, 2014, 06:45:40 PM »
I prefer to collect a sample in a small (8 floz) mason jar, seal it and pop it in the freezer to chill to close to the calibration temp for your hydrometer. The correction tables get less accurate farther from the calibration temp and if you let it chill uncovered continued evaporation can give you a higher than accurate reading.

I put the sample into a metal cocktail shaker.  That gets swirled around in a bowl of ice water.  In less than 60 seconds I can go from boiling to 60F.
^^^^^^ I have been using this method after reading Denny post about it on another thread. My hydrometer is calibrated to 69 degrees so I bring it close to that.
I take the gravity as the boil is finishing and then proceed from there: boil a few extra minutes if almost there, knowing I'll lose a little volume, add dme if more than a couple points off, add water if gravity is higher than desired then I test again when cool and record OG in my notes.
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Re: BIAB and OG (yes another BIAB thread)
« Reply #11 on: November 19, 2014, 04:53:53 AM »
I put a tsp or so in an old White Labs vial. I seal it to prevent evaporation then drop it in a cup of ice water. Its ready to read before I hit a boil and I can decide if I need to add DME. I use a refractometer, so this may not work if you use a hydrometer.
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Re: BIAB and OG (yes another BIAB thread)
« Reply #12 on: November 19, 2014, 03:10:52 PM »
DME is about 40 points per pound per gallon.

DME carries points per pound per gallon (PPG) value of 46.  DME's PPG value is used to determine the maximum extract possible from a batch of malt based on it's dry basis, fine grind (DBFG) percentage

Briess 2-Row DBFG = 80.5%

Briess 2-Row extract in PPG = 0.805 x 46 = 37 PPG

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Re: BIAB and OG (yes another BIAB thread)
« Reply #13 on: November 19, 2014, 03:37:08 PM »
OK, so based on the recipe I should let the extract guide me as far as shorter & longer boil or adding DME? Any charts to help guide this?

As others have said before, I think this is a BIG test batch until I get it dialed in...

If you want to boil down to a gravity, you need a way to measure how much liquid in is your kettle.   One way is to take a piece of wood, plastic, or metal and mark off fractions of a gallon by incrementally adding  fractions of a gallon of water to your kettle.  Another way is to compute the amount of liquid in a kettle using a metal ruler.  A kettle can be treated as a cylinder.  The volume of a cylinder in square inches is computed using the following formula:

kettle_volume = radius x radius x 3.14 x height_of_the_fluid_column

For example, one of my smaller kettles has a diameter of 12 inches.  If I measure 8 inches of wort in this  kettle, then kettle_volume = 6 x 6 x 3.14 x 8 = 904.32 cubic inches.

There are 231 cubic inches in a gallon; therefore, the kettle contains 904.32 / 231 = 3.91 gallons of wort.

With that said, if you collect 6.5 gallons of 1.038 wort and you want to hit 1.060, then your final volume should be 38 / 60 x 6.5 = 4.12 gallons.  In this case, you will probably want to add DME.

Dividing your collected volume by your desired volume and multiplying the collected volume S.G. by that value gives you the S.G. at the desired volume if you do not nothing other than reduce the amount of water in the batch of wort.

6.5 / 5 x 0.038 + 1.0 = 1.0494

Subtracting the S.G. at the desired volume in points from the desired S.G. in points and multiplying by the desired volume gives one the number of points of extract that need to be added to make up for the shortfall from the mash.

60 - 49.4 x 5 = 53 points

Using 46 as the number of gravity points available from a pound of DME yields:

53 / 46 =  1.152 pounds, or roughly 18.5 dry ounces of DME.
« Last Edit: November 19, 2014, 03:40:47 PM by S. cerevisiae »

Offline Stevie

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Re: BIAB and OG (yes another BIAB thread)
« Reply #14 on: November 19, 2014, 03:40:17 PM »
DME is about 40 points per pound per gallon.

DME carries points per pound per gallon (PPG) value of 46.  DME's PPG value is used to determine the maximum extract possible from a batch of malt based on it's dry basis, fine grind (DBFG) percentage

Briess 2-Row DBFG = 80.5%

Briess 2-Row extract in PPG = 0.805 x 46 = 37 PPG
I've always used what Palmer lists in How to Brew, 40-43 points per gallon. 40 is also an easy number to work with as it is easily divisible by 5 or 10 gallons.