Gravity Readings?

[hamstringsally]

Interestinggggg.... I wouldve thought that youre errors may have been from temperature related issues.

Well then, I'll go sit back under my rock for a little bit.


Sponge

all good i really appreciate the feedback mate

 

[tallie]

hey tallie,


cos ive only got 2 vessels i mash in one then take first runnings and put then into the fermenters till after i sparge and then put everything back into the boil pot. I measured out everything that went into boil pot before boil to see how much so i definatly know i started with 144l.

i stirred up and took a reading and temp would have been around 70 deg atm before boil to start my 60min and hop additions. at the time read 1.039

after hour boil i took OG reading at say 98 deg which came out at 1.040

So the more i think about it there could be a few reasons why it dosent add up that i can think of

1. different temps when taking readings?

2. I did not add (measure) what was left over in the bottom of the boil pot after boil which could be between 3 and 7l of hops ect (dont use hop bags) which i will do next time for the exercise. maybe this could be my novice mistake?

Yep, sounds like a combination of the above. If you're using a hydrometer, it'll be calibrated to a certain temperature. The hotter the liquid, the less dense it will be, which will result in a lower gravity. If you're not measuring the liquid at that temperature the hydrometer was calibrated at, then you have to make an adjustment (there are calculators out there to allow you to do this) or cool the sample down. Also, assuming it's a glass hydrometer, be careful with putting it in hot liquids! Ignore that; just saw your follow up post Although, I did find that when I started cooling my refrac samples down, I got much more consistent results with my hydrometer readings. Could be worth a try.

The other thing is that it seems you're basing the volume measurements from the fermenters - are they plastic? If so, you could be getting some distortion/expansion from the hot liquid that could be throwing your volumes out. If you've got a straight-sided cylindrical kettle, you can make a measuring stick to work out your volume based on the depth of the liquid.

And yes, when using the above calculations for the expected gravity, you need to take all the final liquid into account; not just what you transfer to your fermenters.

Cheers,
tallie

 

[hamstringsally]

Yep, sounds like a combination of the above. If you're using a hydrometer, it'll be calibrated to a certain temperature. The hotter the liquid, the less dense it will be, which will result in a lower gravity. If you're not measuring the liquid at that temperature the hydrometer was calibrated at, then you have to make an adjustment (there are calculators out there to allow you to do this) or cool the sample down. Also, assuming it's a glass hydrometer, be careful with putting it in hot liquids! Ignore that; just saw your follow up post Although, I did find that when I started cooling my refrac samples down, I got much more consistent results with my hydrometer readings. Could be worth a try.

The other thing is that it seems you're basing the volume measurements from the fermenters - are they plastic? If so, you could be getting some distortion/expansion from the hot liquid that could be throwing your volumes out. If you've got a straight-sided cylindrical kettle, you can make a measuring stick to work out your volume based on the depth of the liquid.

And yes, when using the above calculations for the expected gravity, you need to take all the final liquid into account; not just what you transfer to your fermenters.

Cheers,
tallie

thanks heaps tallie. yeah the fermenters are the standard plastic ones so that could be the problem too. I need to sit down and understand and learn more re theory side of brewing so can get better control and better understanding of exactly whats going on, why and how to tweak things along the way.
just about to set a computer up in the brew shed and put a program on it which i think will help me hopfully and more attention to detail with whats going on.

thinking beersmith but some people also rate pro mash?

 

[Deebo]

I cant think of any reason a preboil sample would be the same as post boil other than the following:
1. The readings are stuffed (temperature.. evaporation on the refract.. or something else weird) I would say this is most likely
2. You added water (or it was raining)
3. Nothing boiled off

The amount of trub/wort left in the kettle or the volume in fermenter will really only help you work out efficiency.. it wont explain why your preboil and postboil gravities are almost the same.

 

[Helles]

I do 80-90lt batches on a fairly new system
started at 70% eff found i needed to stir the mash every now and then
to come to 84%eff
i also check mash gravity with refractometer at end of mash to give me an idea of OG and boil volume