Calculate This

[cubbie]

So i had a few problems today. To start with my mash tun dropped 3 degree. I was meant to be mashing at 67 and when i checked the temp after 60min it was 64... mmm that has never happened before. Then missed my mash out temp and almost missed my sparge temp.

So anyway after all that I had about a 73-74% efficiency into the kettle 1.040 at 31 litres. No wthe next gravity I take is in the feremter moments after I pitch the yeast. Gravity of 1.042? how can that be. I boiled off to 24 litres. That is a 59% efficieny!!! Ok so how can I get these numbers?

 

[Thirsty Boy]

you measured something wrong...

was your 24L your post boil volume or your fermentor volume? What temperatures did you measure at? The same each time? Hydrometer or refractometer?

you have "lost" 232 gravity points... thats the equivalent of 5.5L of your fermentor wort (not unfeasible... 3-4 for trub and 1L to thermal shrinkage) OR to mis measuring your gravity by 8 points (or 4 at either end) - or to some combination of smaller errors.

I know that some people were reporting magical losses of efficiency between pre & post boil... but even those weren't this drastic, so I am afraid the answer is that you buggered something up.

 

[jimmy01]

I agree with Thirsty Boy - maybe measurement error somewhere. I have been guilty of this myself - particularly with volume measurements.

However I have also noted some brews where the gravity loss pre and post boil seems to be too big simply for measurement error.

I have long wondered about the effect of the hot break on GU's. The pre-boil SG is taken whilst protein is in suspension. The post boil gravity (particularly if done in the fermenter) is taken after a lot of the protein has dropped out of solution. Surely this must reduce total GU's.

What do you think?

Cheers

Jimmy

 

[Screwtop]

How did you measure your pre boil 31L and how did you measure your volume in the fermenter. Measuring pre boil I always make a temp correction as the wort is usually somewhere around 70C - 80C depending on whether I've started the burner prior to measuring. I always measure in the kettle, use a pre calibrated dipstick or use a metal ruler and do the old PI()R^2Measured depth. Due to the temp I usually need to reduce the pre boil volume by about 1.25 litres then I make the mash efficiency calculation and subtract the boiloff volume for my kettle. Don't use percentages just the amount you loose in litres per hour in your kettle at your normal boil rate, percentage calcs vary with the volume of preboil wort. After the boil I measure again and do the temp calc again at 4% to arrive at my post boil volume of cooled wort and compare this to the calculated volume, it's usually very close. If you are using the marks on your fermenter as an indicator of volume in the fermenter, they are not very accurate and can vary from fermenter to fermenter. Simply use the volume post boil in your kettle. To calculate what you need post boil start with the amount you want in the fermenter and add on your losses, kettle trub, chiller etc.

Cheers,

Screwy

 

[bradsbrew]

Speaking of calculating efficiency.....is what I do correct (surely its that this simple).

Only use Qbrew. Using 5.4kg grain OG should be 1058, after boil and 22L in the fermenter I have an OG of 1049.
So all I do is 49 divided by 58 x 100 = 84.48% efficiency ??? Surely I cant be getting this sort of efficiency from my dodgy set up.

Cheers Brad

 

[mika]

With a batch size of 22L and 5.4kg of generic grain, 100% efficiency (virtually impossible in the homebrew world) should give you ~1078 OG. To get a 1058 OG, the recipe efficiency setting is 74%. If you then only achieve an OG of 1049, then you're efficiency is 84.84% of 74% (recipe efficiency setting) or in other words ~63%.

 

[bradsbrew]

With a batch size of 22L and 5.4kg of generic grain, 100% efficiency (virtually impossible in the homebrew world) should give you ~1078 OG. To get a 1058 OG, the recipe efficiency setting is 74%. If you then only achieve an OG of 1049, then you're efficiency is 84.84% of 74% (recipe efficiency setting) or in other words ~63%.

Yep you are 100% correct Mika just checked the configuration of the Qbrew setting and its set to 75% that makes more sense.

Cheers Brad

Edit- Just also found that I can set it to metric instead of doing the conversions myself. Doh

 

[Thirsty Boy]

Screwy is spot on... you need to take all your measurements in the same way, at the same temp - or they can really get thrown out.

I take a different tack to screwy (his method is perfectly good though) - I measure everything at boiling. I take my pre-boil volume, just after the kettle has come to the boil. Gas off for a second, measure volume (calibrated dipstick) and take a gravity sample - gas back on. Same at post boil. Measure just after I turn off the gas.

I calculate my batch size as my "hot" post boil volume - in the knowledge that that will equate to about 1L less once its cooled down. So as Screwy said, you work out your volumes by going backwards from your desired amount of package beer. For me that means - 19L in the keg + 1L lost to yeast trub + 2.3L lost to hops and break in the kettle + 1L shrinkage = 23.2L, thats my batch size. I boil for 90mins and lose 6.8L so my pre-boil is 30L

This measurement hot - that one cold and suddenly its 4% error this way 4% error that way and you are out by 8%

jimmy01 - there was a bit of talk about the contribution of protein break to loss of gravity points, when the "amazing efficiency loss in the kettle" mystery was a hot topic. Someone found a paper discussing exactly that topic and the figures worked out (if I recall correctly, and I might not) to be about 0.5-1% change in the gravity from pre to post boil. Not a lot, but not insignificant. I suspect that that could be one of the reasons that its quite traditional to only call your boil "started" once you see the hot break happen. Hot break happens, take a quick sample and call the boil started. Then the majority of the effect of protein on the gravity figures is negated because the protein has already precipitated before your first reading. or something like that.

TB

 

[jimmy01]

jimmy01 - there was a bit of talk about the contribution of protein break to loss of gravity points, when the "amazing efficiency loss in the kettle" mystery was a hot topic. Someone found a paper discussing exactly that topic and the figures worked out (if I recall correctly, and I might not) to be about 0.5-1% change in the gravity from pre to post boil. Not a lot, but not insignificant. I suspect that that could be one of the reasons that its quite traditional to only call your boil "started" once you see the hot break happen. Hot break happens, take a quick sample and call the boil started. Then the majority of the effect of protein on the gravity figures is negated because the protein has already precipitated before your first reading. or something like that.

TB

Thanks TB.

As I said I have always wondered about this.

Cheers
jimmy

 

[cubbie]

Thanks guys. I have done some recent recalibration of my volumes, but I am still not happy with them, I need to do it again. Thirsty I can't use you method as I have an immersion chiller so unless i work out the displacement of my chiller it is a bit hard to take a post boil volume at flame out, but I understand I need to get more confidence in these volumes.

I only have a hydrometer at the moment (need at refractometer, though my LHBS quoted me $100+ for one on Sat, mind you his temp dials were only $26), both my readings where taken at 20c.
Yes 31L was pre-boil (volume measured at aprox 70c), 24L was post boil (measured in the fermenter with losses added back on).

Gravity points can't just disappear so as suggested I guess this is a case of being more accurate when/how i take measurements be it SG, volume, temp etc. If you know you OG and volume and hit you final volume then surely you FG will be entirely predictable? Is that correct?

Thirsty, I like the idea of taking the pre-boil volume and gravity once you reach a boil, I think the pre-boil volume should be pretty predictable esp if you batch sparge. My question re this is, what are your losses/changes if any in volume and gravity as you bring the wort to the boil? Are these accounted for?

Where are people taking their post-boil gravity? In the kettle or fermenter or both?

Cheers.

 

[Thirsty Boy]

I'm not getting any significant change in volume between 70C and 100C .. I just double check to make sure that I still have the 30L pre-boil that I want. Mainly I measure then to eliminate the hot break problem and to ensure that a little bit of boiling has mixed everything up well so I am getting a nice accurate reading + just to be anal about consistency. Pre and post both at 100C... then I know that thermal shrinkage cant be an issue.

It doesn't matter when, or really how you take your volumes... just so long as you do it the same each time and you know about the effect that temp can have. Once you have the pre-boil volume and gravity... you can work everything out from there.

I am stickler and have calibrated pretty much everything in my brewery... so I'm confident to withing about 0.5L for all my measurements --- but in a 23 L batch, that's still +/- 2% every time I measure something.

Given that you dont change things... all the volumes and boil offs etc etc, should end up being quite predictable (gravity less so) - yeah, a few little variances around the edges, but fundamentally you should be able to look at your mash tun and know what you will end up with in your fermentor.

TB

 

[Peter Wadey]

Thanks guys. I have done some recent recalibration of my volumes, but I am still not happy with them, I need to do it again. Thirsty I can't use you method as I have an immersion chiller so unless i work out the displacement of my chiller it is a bit hard to take a post boil volume at flame out, but I understand I need to get more confidence in these volumes.

I only have a hydrometer at the moment (need at refractometer, though my LHBS quoted me $100+ for one on Sat, mind you his temp dials were only $26), both my readings where taken at 20c.
Yes 31L was pre-boil (volume measured at aprox 70c), 24L was post boil (measured in the fermenter with losses added back on).

Gravity points can't just disappear so as suggested I guess this is a case of being more accurate when/how i take measurements be it SG, volume, temp etc. If you know you OG and volume and hit you final volume then surely you FG will be entirely predictable? Is that correct?

Thirsty, I like the idea of taking the pre-boil volume and gravity once you reach a boil, I think the pre-boil volume should be pretty predictable esp if you batch sparge. My question re this is, what are your losses/changes if any in volume and gravity as you bring the wort to the boil? Are these accounted for?

Where are people taking their post-boil gravity? In the kettle or fermenter or both?

Cheers.

Cubbie,
If the immersion chiller is not fully submersed at the end of boil, then yes you would have a problem with calibration/ working out post boil volume....... unless you quickly lift the coils clear of the top of the wort to take a measurement.

However if the coils are fully submersed at end of boil, then work out the displacement of the chiller (not hard) and subtract it from the post boil wort volume.


Pete

 

[cubbie]

Pete,

Yeah it is not full submersed, but i could probably work out the displacement for say when I am at 23L or 24L etc