Help with hitting Target O.G.

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kozydogg

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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.
 
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.
 
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.
 
Northcalais40 said:
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.
Click to expand...

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.
 
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.
 
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.

Sent from my SPH-L720 using Home Brew mobile app
 
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?
 
green_lantern11 said:
It should always be a 10pt rise in gravity per 1 gal of boil off.
Click to expand...

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.


Sent from my iPhone using Home Brew
 
green_lantern11 said:
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?
Click to expand...

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.

Sent from my SPH-L720 using Home Brew mobile app
 
kozydogg said:
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.
Click to expand...

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.

Sent from my SPH-L720 using Home Brew mobile app
 
I keep a rolling boil. Nothing crazy. My kettles have a lot of surface area, so I always have a 2 gal/hour boil off. My mash efficiency varies depending on the grain bill, but I'm usually close. For this particular batch my pre boil gravity was 1045 with 7.25 gal. Post boil vol was 5.25 gal. 45 x 7.25 = 326. 326 / 5.25 = 62. I should have 1062 OG. I don't. I have 1056.
 
balazs said:
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.

Sent from my SPH-L720 using Home Brew mobile app
Click to expand...
Boil rate is always the same. 2 gal for 60min. I always keep a rolling boil. Here is an example. Last week I made a stout. My pre boil gravity/volume was 1054/7.25. Post boil was 1064/5.25. Now, if you do the math and convert this to gravity points we get: (54 x 7.25) = 391.5. 391.5/5.25 = 74. 1064 is a full 10 points lower than 1074. All readings are correct, double checked, thouroughly stirred, corrected for temperature and calibrated. Is the sugar magically jumping out of my kettle? What am I missing here?
 
That is strange. Not quite sure where else to look into fixing that.

Sent from my SPH-L720 using Home Brew mobile app
 
green_lantern11 said:
Boil rate is always the same. 2 gal for 60min. I always keep a rolling boil. Here is an example. Last week I made a stout. My pre boil gravity/volume was 1054/7.25. Post boil was 1064/5.25. Now, if you do the math and convert this to gravity points we get: (54 x 7.25) = 391.5. 391.5/5.25 = 74. 1064 is a full 10 points lower than 1074. All readings are correct, double checked, thouroughly stirred, corrected for temperature and calibrated. Is the sugar magically jumping out of my kettle? What am I missing here?
Click to expand...

Your math is correct so that means your measurements aren't. If you double checked them then that means you're making the same mistake(s). You need to stop and see where you're making an assumption and then check if the assumption is valid.

Lets say your 7.25g is accurate as were your gravity readings. That would mean your post boil volume was 54/64x7.25=6.12 which is a pretty typical boil off. When are you measuring post boil volume? By any chance is it after removing your hop bag?


Sent from my iPhone using Home Brew
 
BackAlley said:
Your math is correct so that means your measurements aren't. If you double checked them then that means you're making the same mistake(s). You need to stop and see where you're making an assumption and then check if the assumption is valid.

Lets say your 7.25g is accurate as were your gravity readings. That would mean your post boil volume was 54/64x7.25=6.12 which is a pretty typical boil off. When are you measuring post boil volume? By any chance is it after removing your hop bag?


Sent from my iPhone using Home Brew
Click to expand...
Right there is the problem. My post boil volume reading is 5.25 gal. It's a 2 gal / hour boil off. Very high. But, I do have 15 gal kettles with a lot of surface area. It's the MoreBeer Tippy System (http://morebeer.com/category/morebeer-tippydump-sculptures.html). I do not use a hop bag, so my hops are completely broken up in the liquid. But, that shouldn't be a factor. I mean it's only around 2.5 ounces of pellets for this particular batch. Chiller is removed before measuring post boil volume as well. I put the same measuring stick in the liquid that I used for pre boil measurement. It's always a 2 gal loss. We're almost there. Keep digging. :)
 
If you are getting 7.25 gallon of 1.050 pre-boil wort, then you will end up with 5.25 gallons of 1.069 wort. Nothing can change that. If you aren't coming up with the same numbers in real life then your measurements are wrong. There isn't any other explanation.

Are you stirring the pre-boil wort? The wort can stratify, sometimes leaving you with a sample that contains more sugar than is representative of the rest of the wort. How do you know your hydrometer is accurate? How do you know your volume measurements are accurate?
 
LovesIPA said:
If you are getting 7.25 gallon of 1.050 pre-boil wort, then you will end up with 5.25 gallons of 1.069 wort. Nothing can change that. If you aren't coming up with the same numbers in real life then your measurements are wrong. There isn't any other explanation.

Are you stirring the pre-boil wort? The wort can stratify, sometimes leaving you with a sample that contains more sugar than is representative of the rest of the wort. How do you know your hydrometer is accurate? How do you know your volume measurements are accurate?
Click to expand...
I agree with you that there is no other explanation. Both pre boil and post boil wort is thoroughly stirred. My measuring stick was calibrated by pouring one quart of water into the kettle and making a hash mark. I did this one quart at a time up to 7.5 gallons. My hydrometer has been calibrated at 60F with distilled water and the measurements are backed up with a refractometer that is also calibrated with distilled water. The refractometer is self adjusting for temp.
 
green_lantern11 said:
We're almost there. Keep digging. :)
Click to expand...

I'll go for one more suggestion and then I'm out. You keep saying that all your measurements are correct but clearly one or more must be erroneous. It's actually quite frustrating.

You said you marked off your stick one quart at a time. That means by the time you got to 7.5g you've measured 30 individual quarts. Every measurement has error and if your quart wasn't accurate or you made a systematic filling error, that would compound itself. Have you tried measuring the diameter of the pot accurately and comparing the calculated volume to your stick?

The formula for volume in gallons is:
V = d x D^2 /294.1

Where d is depth of wort and D is the pot diameter. This ignores any equipment inside the pot but I'm assuming that's negligible.


Sent from my iPhone using Home Brew
 
You know your equipment and system better than we do. You're going to have to find where the error is. We can't do that for you, we can only offer suggestions. The scenario that you are presenting to us is not possible without an error of measurement somewhere in your system.
 
I'll try the formula. I've actually measured out that kettle 3 times using different measuring quarts. Believe me, no one is more frustrated than me. I really appreciate all the help. Thanks again for taking the time. Cheers.
 
I was just hoping you would catch something I didn't. I'm gonna try the formula that ALLEY suggested. Thanks for all the help. I appreciate it.
 
You say your pre-boil measurement is adjusted for temperature. Does this mean you cool off the wort before measuring, or does it mean you measure hot wort, check its temperature, and use a correction for this?

I find that if I measure hot wort and calculate the "correct" SG using Beersmith or similar tools, the number I get is higher than when the wort has cooled off. In other words, if I measure hot pre-boil wort, I will overestimate my pre-boil SG. Could this be your issue?
 
Both actually. I've taken readings and adjusted for temp and I've waited until it gets down to the calibrated temp of 60F. Same number.
 
del said:
I find that if I measure hot wort and calculate the "correct" SG using Beersmith or similar tools, the number I get is higher than when the wort has cooled off. In other words, if I measure hot pre-boil wort, I will overestimate my pre-boil SG. Could this be your issue?
Click to expand...

I find that the temp-corrected gravities of a sample at 150 degrees vs. the same sample at 60 degrees are within a point or two of each other. Well within the margin of error in reading a hydrometer.
 
Yeah, you know... they really should be. The properties of hot liquids are actually quite well known, so it really bothers me that I've had this issue. I really don't know what could be causing it. I think I'll do a session where I heat water to different temps with it and check the calibration.
 

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