# Final Gravity always lower than predicted.



## Dan Pratt (11/1/14)

Just putting it out there to see what you gain from preboil gravity to OG?

I often hit preboil gravity and preboil volumes no worries but my OG is always about 3points lower, only gaining on average about 6-7points from a 90min boil. 

How is everyone else doing?


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## Acasta (11/1/14)

I'd say its due to a loss from kettle to fermenter. That usually occurs from trub losses. What is your brewing process, what is your trub like and whats the volume of it?


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## timmi9191 (11/1/14)

if its a constant diff, as Acasta says - its part of the process.

adjust your software settings accordingly..


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## manticle (11/1/14)

Post boil volumes as predicted?


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## Dan Pratt (11/1/14)

Acasta said:


> I'd say its due to a loss from kettle to fermenter. That usually occurs from trub losses. What is your brewing process, what is your trub like and whats the volume of it?


mashing in 5kg of malt into 28ltrs water for the usual 66c rest then mash out at 78. sparging to get to preboil volume to allow for mt 13% boil off rate and aim for 21lt into the FV, leaving 3.5lts of trub. I boil for 90 mins. use beersmith 2.2 and have the Tot Efficiency set at 75% - it tells me my mash eff is getting 86% + each brew but my brewhouse eff is getting under 70% - is this where its letting me down??




manticle said:


> Post boil volumes as predicted?


I have only just adjusted the water absorption in advanced settings, after my calculations Im only absorbing 720mls per 1kg of grist, it was set at 960mls and i was getting about 1.5ltrs too much into my fermenter. I thought ths was the problem but even today the volumes were right but the Gravity into the FV was low again 

Generally my predicted post boil will be 24.5 - which is 21lts ( FV vol ) + 3.5lts (Trub )

Whats your average gain from a 90mins boil? 6 - 8 - 12 points??


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## manticle (11/1/14)

To be honest, I only ever measure if there's a recurring problem. I calculate X L into ferment @ Y gravity and am usually within a beesdick.

If I was consistently off, I would go back to basics, measure every stage and find out where the problem was occurring, then try and fix it.


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## Dan Pratt (11/1/14)

With that in mind, my brewhouse eff is only averaging just under 70% then, it's set at 75. I'm getting high 80s for mash eff and hitting preboil gravitys but just can't seem to get that OG. 

How do you sparge?


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## damoninja (12/1/14)

I've miraculously hit every brew on the nose with the exception of one, where I came in 10 points higher than anticipated. But, it was a porter so kind of worked out, drinking the first bottle now :icon_drool2:

*Edit: *Don't drink and type


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## Dan Pratt (12/1/14)

Any ideas on how to improve my brewhouse efficiency? 

My mash on the BM is like I have stated well up in the high 80% each brew. My boil is not aggressive and evaps at 13%per hour and I get final volumes.....??? 

This is all based on beersmith calcs, I'd there a simple formula I can run some numbers through to double check?


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## Dunkelbrau (12/1/14)

If you are hitting your mash numbers (pre boil gravity AND volume) it's not a mash side, it's boil off rate.

I have a feeling your pre boil volume might be a little low and your evap rate is set too high, so you think you are hitting post boil volume but your gravity is lower because you haven't boiled to match your rate in beersmith.

Double check your pre boil volume, (maybe grain is absorbing more or you're leaving more behind) and gravity and recalculate your boil off rate.


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## manticle (12/1/14)

Pratty1 said:


> With that in mind, my brewhouse eff is only averaging just under 70% then, it's set at 75. I'm getting high 80s for mash eff and hitting preboil gravitys but just can't seem to get that OG.
> 
> How do you sparge?


batch at about 74


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## Screwtop (12/1/14)

Pratty1 said:


> Any ideas on how to improve my brewhouse efficiency?
> 
> My mash on the BM is like I have stated well up in the high 80% each brew. My boil is not aggressive and evaps at 13%per hour and I get final volumes.....???
> 
> This is all based on beersmith calcs, I'd there a simple formula I can run some numbers through to double check?


Boil off % can be a trap. As the boil off volume calculated from a percentage depends upon the pre-boil volume ie: 13% of 32L = 4.16L Using a percentage any variation in pre-boil volume will result in a variation in boil-off volume, when in fact boil-off should vary very little due to changes in pre-boil volume. Largely kettle surface area and applied heat determines boil off rate. All things being around average on your brewday, same kettle dimensions, similar boil rate, ambient temp and air movement around and over the kettle your boil off rate should be roughly the same volume each time. Set the boiloff in Beersmith as a volume from your records not a percentage. If I make a single batch I lose 8L over 90 min (5.4L PH) to boil off just the same as if I do a double batch. Beersmith would calculate a difference of almost double the boil-off volume for the double batch. Also just set all of your deadspaces and volume losses to zero. Set the batch volume to allow for these and you should find the calculated values more acurate.

And by the way I generally gain around 6 to 8 gravity points over a 90 min boil (not what Beersmith calculates by the way), mash eff is over 90% and brewhouse around 85%. I take the pre-boil gravity which is usually above what Beersmith predicts and know the end of boil will be around 6 points higher on my system.

Hope this helps you get to the bottom of the disparity.

Screwy


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## warra48 (12/1/14)

Just to put a different perspective on this.

If you are achieving consistent results, then you do not have a problem! Simply add a little more malt to give you the extra 3 points or so.
You are brewing to make yourself a nice beer, not to hit some predicted figures thrown up by BS software.

I use BeerSmith2, but basically for recipe design, and to keep a record of my brews. I don't use it for volumes for mashing or sparging etc. I mash, I drain, I sparge, and top up with water to hit 34 litres pre-boil. My OG into the fermenter is usually within 2 or so points from predicted, but it's consistency you are after.

If you still think you have a problem, look at your system to see if there is anywhere you can reduce losses. Then simply adjust your brewhouse % to give you your desired OG outcome.

edit: I agree with Screwtop about boil off %. Boil off is in reality not a % issue, but a volume issue. This is one of the weaknesses in BS software. It is dependent on the surface area of your kettle, boil intensity, and to a lesser degree ambient conditions such as temperature and humidity. For example, in the same kettle your boil off volume will be much the same, whether you start with say 20 litres or 30 litres, but the % will vary significantly.


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## adryargument (12/1/14)

I simply set my recipe design at a rediculously high efficientcy.
That way whenever i hit it its an achievement and i deserve a 6 pack or two.

More challenging and enjoyable brewday.

Edit::: If i keep raising the bar, and keep celebrating with the previous 'efficient' brews... I sense a failure-over-time predicament.


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## fletcher (12/1/14)

adryargument said:


> I simply set my recipe design at a rediculously high efficientcy.
> That way whenever i hit it its an achievement and i deserve a 6 pack or two.
> 
> More challenging and enjoyable brewday.
> ...


that's a really helpful and much needed response.

i'm the same as you pratty, so have been reading this with interest. i'm going to double check what jurt has said; checking my volumes, but more importantly, how i've measured them on everything.

i've recently checked the measuring of my volumes. i measured 1L of water on my scale, poured it in and marked the kettle and fermenter etc until i had my proper volumes marked. i was WAY off from when i initially measured them.


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## Acasta (12/1/14)

Pratty1 said:


> Any ideas on how to improve my brewhouse efficiency?
> 
> My mash on the BM is like I have stated well up in the high 80% each brew.





Pratty1 said:


> mashing in 5kg of malt into 28ltrs water for the usual 66c rest then mash out at 78. sparging to get to preboil volume to allow for mt 13% boil off rate and aim for 21lt into the FV, leaving 3.5lts of trub. I boil for 90 mins. use beersmith 2.2 and have the Tot Efficiency set at 75% - it tells me my mash eff is getting 86% + each brew but my brewhouse eff is getting under 70% - is this where its letting me down??


3.5L of trub left in the boiler seems quite high to me and I'd say that's where your losses are. Do you use whirfloc (or similar) and how much do you use? I don't use a BM so I'm not sure if that amount of trub is high or not? What's your crush like?

There are a few ways to deal with high trub losses. One is to just adjust brewhouse eff in beersmith and accept that the system IS under %70, which is totally fine! You are still making beer and it probably only costs you a few $ extra in grain.

If you do want to increase the brewhouse eff, you can run off the 3.5L of trub into a separate container and put it in the fridge, after a few hours (preferably over night) it will separate and you can pour off the clean wort, which would add more to your FV and increase your OG. This was is a bit more work, but if you feel like you want to increase the eff I would go for this method. A lot of people say don't worry about the numbers ect. I enjoy the challenge and optimizing the system.


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## Dan Pratt (12/1/14)

Hi All, thankyou for the responses, time to brew again to get my volumes right.

On the 3.5 lts of trub acasta that is normal for a BM, i have it tilted with a 2 x 4 under the rear leg and thats the most it will get out of it. Thats a good idea to keep the trub, coolin teh fridge and decant the wort, id use that for a starter though, 

I have made some changes to my BS software for grain absorption and my brewhouse efficiency is now at 70%.


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## donald_trub (17/1/14)

This is a very timely thread for me. I just completed my first all grain batch last Friday. I've got a new Techniice mash tun and a new Crown 40L urn. I measured out the water on the urn and marked the sight tube. I checked the boil off rate by boiling 25 litres of water for an hour. I think from memory it was close to 3 litres, but will need to check when I get home. Mash tun dead space and loss to trub were guessed for now.

I hit my pre-boil gravity and volume spot on and I was chuffed at that. At the end of the boil, I seemed to be way under on the gravity reading going in to the fermenter. I was left scratching my head at this.

I think I'm going to bump up the amount of trub lost in the kettle. I think I said 1 litre but there may have been a bit more than that. I'll also double check my sight tube markings. I was using a 2 litre plastic jug to do the markings. I'll look at weighing out each litre. Luckily I only used a whiteboard marker for now!


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## wide eyed and legless (17/1/14)

If you are going to physically measure pre and post boil volumes to calculate your loss to evaporation you cannot measure from ambient temperature, but the measurement at the start of the boil (use a tape or a rule ) then measure again at the end of the boil. 
If you are measuring at ambient temperature you will than have to calculate in the thermal expansion of the liquor.


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## Parks (17/1/14)

Screwtop said:


> Also just set all of your deadspaces and volume losses to zero. Set the batch volume to allow for these and you should find the calculated values more acurate.
> 
> And by the way I generally gain around 6 to 8 gravity points over a 90 min boil (not what Beersmith calculates by the way), mash eff is over 90% and brewhouse around 85%. I take the pre-boil gravity which is usually above what Beersmith predicts and know the end of boil will be around 6 points higher on my system.
> 
> Screwy


Sounds like you aren't using Brewhouse Efficiency as the same definition as BS does.

I have set all my volume losses and am now starting to get predictable results in gravities and volumes in the software. So much nicer having it setup properly and not having to adjust values outside of it.

The boil off % option was one of the no.1 things they added when BS version 2 came out. That certainly made life easier.


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## SJW (24/1/14)

Screwtop said:


> Boil off % can be a trap. As the boil off volume calculated from a percentage depends upon the pre-boil volume ie: 13% of 32L = 4.16L Using a percentage any variation in pre-boil volume will result in a variation in boil-off volume, when in fact boil-off should vary very little due to changes in pre-boil volume. Largely kettle surface area and applied heat determines boil off rate. All things being around average on your brewday, same kettle dimensions, similar boil rate, ambient temp and air movement around and over the kettle your boil off rate should be roughly the same volume each time. Set the boiloff in Beersmith as a volume from your records not a percentage. If I make a single batch I lose 8L over 90 min (5.4L PH) to boil off just the same as if I do a double batch. Beersmith would calculate a difference of almost double the boil-off volume for the double batch. Also just set all of your deadspaces and volume losses to zero. Set the batch volume to allow for these and you should find the calculated values more acurate.
> 
> And by the way I generally gain around 6 to 8 gravity points over a 90 min boil (not what Beersmith calculates by the way), mash eff is over 90% and brewhouse around 85%. I take the pre-boil gravity which is usually above what Beersmith predicts and know the end of boil will be around 6 points higher on my system.
> 
> ...


Nice to see your still giving good sensible advice Screwy.
I have not been on for years. Not much has changed. Same questions.....same answers.

Steve


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## damoninja (24/1/14)

+1 to Screwy's advice


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## Screwtop (26/1/14)

SJW said:


> Nice to see your still giving good sensible advice Screwy.
> I have not been on for years. Not much has changed. Same questions.....same answers.
> 
> Steve



Hi Steve, Good to see you popping in. I got the shits with the forum ages ago, battling the opinions of so many google-brewers took it's toll, but the place seems a little more cohesive lately.

Screwy


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