Preboil And Post Boil Gravitys

[browndog]

I did a brew on Sunday morning and as I am trying to work out the efficiency of my set up took plenty of notes and came up with this strange discrepancy. Using Brewsmiths instructions for a 21L batch (in the fermenter) I followed the sparging instructions to the letter and according to my dipstick ended up with the exact number of litres in the kettle, that being 29L. My SG was 1.054, 3 points higher than the 1.051 estimated.
I thought this is great things are going well. I loose 4L per hour boil off based on the last few brews, 3L to trub and allowing for 1L shirnkage, this should see 21L in the fermenter. After cooling the wort I found there was 24L in the kettle and sure enough ended up with 20L in the fermenter. I drained the kettle and found there to be 3L left over.
The only thing I can come up with this that when I made my dipstick I used cold water and when I took the preboil volume the wort while not being boiling, was still hot and showing more than it should on the dip stick. That, or I actually lost 5L in the boil off. Should I recalibrate my dipstick to 70C water ?

cheers

Browndog

 

[JasonY]

I calibrated mine to cold water which may not be as accurate as using boiling water but a lot easier. All I do is make sure I put 27L in the kettle and sure enough I get my 20L in the fermenter. After a few brews you eventually tweak your setting and get it right.

If I were you I would just add an extra liter when you sparge and compensate that way. However do another couple of brews without changing anything to make sure there really is a difference and it wasn't a one off.

If your gravity in the fermenter is higher than anticipated then you can always dilute it a little if you really want 21L. At the end of the day 1L is not that bad as long as your OG isn't miles out.

 

[browndog]

Ah yes Jason, I forgot to mention that my post boil gravity was 8 points lower than the estimated, that made me think that I had not lost enough volume in the boil.


the plot thickens

cheers

Browndog

 

[JasonY]

What is he 1.054 you mention above being 3 pts higher than you had expected? If the preboil gravity was higher than your expected preboil gravity and the volume was correct (or less if the water measured was hot) then it should have been impossible to get 8pts lower in your gravity.

Am I misunderstading the 1.054 or could you have measured it incorrectly? :blink:

 

[AndrewQLD]

Browndog,
What did you take your readings with, Hydrometer or refractometer. If you used a hydro did you cool the samples to 20c before taking a reading? if not then your problem is incorrect hydro reading.
Your final volumes can vary due to atmospheric conditions as well ie, humidity ect. Also ambient air temp can play a part in evaporation to. But these are minor issues.
And finally your efficiency into the fermenter is always variable, if you have a lot of hops in the boiler you will lose more wort to the fermenter ect. I only ever measure my post boil SG from the boiler, this gives you a true indication of your actual efficiency, as apposed to measuring from the fermenter which will give you an overall system efficiency. I measure my efficiency to see how much I am extracting from the grains not to see how much I lose from transfers, hops, boiler ect.

Cheers
Andrew

 

[browndog]

Hi Andrew,
I used a refractometer to take the readings, and yes Jason, the preboil reading was 3 points higher and the post boil reading was 8 points lower than what Brewsmith predicted, this is why I was really confused as to why I was 1L short, I was assuming that I would be 1-2L over!
I guess the logical assumption would be that I incorrectly read the preboil reading.

cheers

Browndog

 

[Ducatiboy stu]

The harder the boil, the more evaporation