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Old 11-08-2010, 10:21 PM   #1
kozydogg
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Default Help with hitting Target O.G.

OK, so here's my situation:

Pretty much every single brew I get good efficiency, but my actual O.G. is almost always lower than my target OG.

For example, I will compare the last two brews I made.

1st brew:

I got a pre-boil gravity of 1.055 at a volume of 7.3 gallons. This equals 93% efficiency and based on that, my predicted O.G. was suppose to be 1.081 (actual target OG was suppose to be 1.073, my software is set to calculate assuming I get 88% efficiency). I ended up getting a 1.067 post boil OG at 4.8 gallons.

2nd brew:

I got a pre-boil gravity of 1.041 at a volume of 7.4 gallons. This equals 86% efficiency and based on that, my predicted OG was suppose to be 1.058 (actual target OG was suppose to be 1.061, my software is set to calculate assuming I get 88% efficiency). I ended up getting a 1.054 post-boil OG at 5.5 gallons.

My brewing methods are as follows:

I dough in at 104, and then usually ramp up using direct fire to get to my mash temp, either 148-156, depending. Oh, for Brew 1 I did a standard 152 mash for 1 hour. For Brew 2 I rested at 144 for 20 min then at 154 for 40 min. I always recirculate my mash. I fly sparge at about a 5 min per gallon. I use a hop bag in my boil and boil vigorously, with no lid. I have a stick with marked gallons on it, so my volume measurements are usually pretty precise. I mill my own grains very fine and my mill setting has stayed EXACTLY the same. Oh, and I'm using a direct fire RIMS system, in case you didn't pick up on that.

My questions:

1. Why are my efficiencies fluctuating?
2. Why am I never hitting my OG, and why is it always lower than my target?
3. How can I get a consistent boil-off rate? (I usually do 75-90 min boils, no lid)


Thanks! sorry if it's a long read.

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Old 11-08-2010, 11:05 PM   #2
jmick
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You must be making some error in measurement along the way - either when measuring Specific gravity or volume. Your numbers don't work out mathematically...

you can predict your post boil gravity by using the formula (pre-boil gravity * volume) = (post boil gravity * Volume) convert your SG to gravity points (ie. 1.055 = 55 points)

For beer 1: let's assume your preboil measurements are correct and your final volume are correct... (55*7.3)= (SG * 4.8) or 401.5 = SG*4.8 divide by 4.8 and you get a predicted post-boil gravity of 1.084. this is not close to what you got.

the second beer gives us the same impossible math.

A couple thoughts... Are you 100% sure on your volume measurements? have you calibrated your hydrometer in distilled water? Are you correcting for temperate when you measure gravity?

Without knowing which numbers to trust, it is very difficult to troubleshoot.

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Old 11-09-2010, 12:18 AM   #3
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for fly sparging, 5 min per gallon is quite fast. Try going as slow as possible. They say to run off 1 quart per min, I don't think I go that slow, but I try. I hear people have troubles when correcting hydro readings for temp, so instead I cool the hot wort with a pie pan floating in a big bowl of ice water. If you are careful to not cross contaminate, the wort is cold in 5 seconds.

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Old 11-09-2010, 12:32 AM   #4
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Quote:
Originally Posted by Northcalais40 View Post
for fly sparging, 5 min per gallon is quite fast. Try going as slow as possible. They say to run off 1 quart per min, I don't think I go that slow, but I try. I hear people have troubles when correcting hydro readings for temp, so instead I cool the hot wort with a pie pan floating in a big bowl of ice water. If you are careful to not cross contaminate, the wort is cold in 5 seconds.
Either I'm retarded or 5 minutes per gallon would be .8 quarts per minute, which would be even slower than your 1 quart per minute.
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Old 02-16-2014, 11:54 PM   #5
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Hey guys. Read your post. I'm having the exact same issue and can't figure it out either. By your post, it sounds like you're an accomplished brewer. I use a more beer tippy system and it sounds like you are too. My OG is always 10 pts lower than what it should be if you do the math like the gentleman suggested in a reply. My measurements are accurate volume wise. I also measure pre boil and OG with a hydrometer adjusted for temp and a refractometer. All of them say the same thing. 10 pts too low. I stir very well, so it's not a false reading. I always get 7.25 gal into the kettle and boil down to 5.3 gal in 60min with a 5.25 transfer to the fermenter. I just don't understand why my OG is always low.

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Old 02-17-2014, 12:32 AM   #6
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It seems your mash efficiency is lower than you think meaning you need more grain to get the OG you are after. Are you using any brewing software? If you are coming up around 10 points shy each batch then you need to recalculate your efficiency to a lower number that matches with preboil gravity and volume.

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Old 02-17-2014, 01:10 AM   #7
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I do. I use three actually. Beer Alchemy, Beer Smith and Beer Tools. Primarily Beer Alchemy though. They all use the simple equation to determine your OG from pre boil gravity and pre and post boil volumes. For me it's always 7.25 gal pre boil and 5.25 gal post boil in 60min. Boil off of 2 gal. It should always be a 10pt rise in gravity per 1 gal of boil off. 2 gal = 20pts. So, say my pre boil gravity is 1050 then any software will tell you your OG should be 1070. A 20pt increase for the 2 gal boil off. But I always get 1060 OG. Mash efficiency should have nothing to do with this calculation. Correct?

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Old 02-17-2014, 01:57 AM   #8
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Quote:
Originally Posted by green_lantern11 View Post
It should always be a 10pt rise in gravity per 1 gal of boil off.
Not sure where you get that. The equation is multiply pre boil gravity times pre boil volume then divide by post boil volume. The higher the pre boil gravity, the greater the increase post boil.


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Old 02-17-2014, 02:17 AM   #9
balazs
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Quote:
Originally Posted by green_lantern11 View Post
I do. I use three actually. Beer Alchemy, Beer Smith and Beer Tools. Primarily Beer Alchemy though. They all use the simple equation to determine your OG from pre boil gravity and pre and post boil volumes. For me it's always 7.25 gal pre boil and 5.25 gal post boil in 60min. Boil off of 2 gal. It should always be a 10pt rise in gravity per 1 gal of boil off. 2 gal = 20pts. So, say my pre boil gravity is 1050 then any software will tell you your OG should be 1070. A 20pt increase for the 2 gal boil off. But I always get 1060 OG. Mash efficiency should have nothing to do with this calculation. Correct?
So are you landing your preboil gravity numbers? If you are then your mash effieciency should be good. Based on the problems that I had when I kept coming up short on my OG, my efficiency was lower than what I was calculating. When I adjusted for that I started hitting my numbers.

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Old 02-17-2014, 02:23 AM   #10
balazs
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Quote:
Originally Posted by kozydogg View Post
OK, so here's my situation:

Pretty much every single brew I get good efficiency, but my actual O.G. is almost always lower than my target OG.

For example, I will compare the last two brews I made.

1st brew:

I got a pre-boil gravity of 1.055 at a volume of 7.3 gallons. This equals 93% efficiency and based on that, my predicted O.G. was suppose to be 1.081 (actual target OG was suppose to be 1.073, my software is set to calculate assuming I get 88% efficiency). I ended up getting a 1.067 post boil OG at 4.8 gallons.

2nd brew:

I got a pre-boil gravity of 1.041 at a volume of 7.4 gallons. This equals 86% efficiency and based on that, my predicted OG was suppose to be 1.058 (actual target OG was suppose to be 1.061, my software is set to calculate assuming I get 88% efficiency). I ended up getting a 1.054 post-boil OG at 5.5 gallons.

My brewing methods are as follows:

I dough in at 104, and then usually ramp up using direct fire to get to my mash temp, either 148-156, depending. Oh, for Brew 1 I did a standard 152 mash for 1 hour. For Brew 2 I rested at 144 for 20 min then at 154 for 40 min. I always recirculate my mash. I fly sparge at about a 5 min per gallon. I use a hop bag in my boil and boil vigorously, with no lid. I have a stick with marked gallons on it, so my volume measurements are usually pretty precise. I mill my own grains very fine and my mill setting has stayed EXACTLY the same. Oh, and I'm using a direct fire RIMS system, in case you didn't pick up on that.

My questions:

1. Why are my efficiencies fluctuating?
2. Why am I never hitting my OG, and why is it always lower than my target?
3. How can I get a consistent boil-off rate? (I usually do 75-90 min boils, no lid)


Thanks! sorry if it's a long read.
Oh, and for boil off rate you need to try and keep the same vigor from boil to boil. Take volume measurements throughout the boil to see if you need to boil harder or softer for the remainder of the boil. You only need a rolling boil. The wort does not need to be jumping in the air. I get 1/2 gallon per half hour boiloff.

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