Gravity Variances

[TyHadaway]

I don't normally take a reading on my pre-boil gravity as I have only been concerned about post-boil gravity in the past. But this time I took a gravity reading pre-boil as I wanted to try out a stepped temperature mash, I may vary the times per step on the next batch of the same recipe just to see what the outcome will be.

My step temperatures on this batch were as follows:

30 min @ 55 degrees Celsius
30 min @ 65 degrees Celsius
30 min @ 75 degrees Celsius and then mash out

In BeerSmith the estimated pre-boil gravity would have been 1.054, although I got 1.073. I am assuming that is due to the fact that I was fly sparking and I got a higher efficiency that I had anticipated.

The part were I am confused is that at post-boil, the gravity in BeerSmith was estimated at 1.062 and after taking a reading, I got 1.047. Both readings were taken at the same temperature of 22 degrees Celsius and it would make sense that the post-boil reading would be higher than the pre-boil as there would be less volume after the boil. Or am I mistaken?

What I am also confused with is that the readings are so vastly different, as I mentioned, I have never taken a post-boil reading before this, so I can't really say if that would be normal or not.

The fermentation has gone off well and I am sitting with a consistent reading of 1.010 after a week and a half and the color and flavor is where I would expect it to be for an Amber Ale and to be honest without having finished my projected fermentation cycle, it has already turned out better than past brews of the same recipe when I have not even racked and aged yet as I also did a first wort addition with my battering hops.

 

[porterpounder]

The post-boil gravity will always be lower than pre-boil. How you take your sample matters. Make sure you stir/mix the wort well before taking a reading as it may stratify/settle. If using a hydrometer, cover the open end of the flask with your hand and tip it back and forth a couple times to mix prior to putting the hydrometer into the flask and give it a spin to shake off any floaty bits that may affect the reading.

 

[Biscuits]

Post-Boil gravity will always be HIGHER than pre-boil. I am wondering if you're confusing pre-boil gravity with your mash gravity? Pre-boil gravity is taken when you have collected both your first runnings and all of your sparge runnings into your boil kettle. This would explain your SG would be lower after your boil.

 

[TyHadaway]

Thanks for clearing that up with regards to the pre-boil and post-boil measurements, not sure then why in BeerSmith, the estimated pre-boil gravity is lower than the post-boil gravity in my recipe, I'll just have to keep that in consideration for future reference.

I do use a hydrometer and I also give it a turn or two after taking a sample to make sure than there is an even consistency in the tube and I check it periodically to make sure that it is calibrated correctly.

Is it normal that the differences in gravity from pre-boil to post-boil to be that different and why is that the case? I do a pretty vigorous boil, not sure if that has anything to do with it.

 

[TyHadaway]

Post-Boil gravity will always be HIGHER than pre-boil. I am wondering if you're confusing pre-boil gravity with your mash gravity? Pre-boil gravity is taken when you have collected both your first runnings and all of your sparge runnings into your boil kettle. This would explain your SG would be lower after your boil.

Yup, took the reading after collecting all the wort into the kettle.

 

[Biscuits]

Thanks for clearing that up with regards to the pre-boil and post-boil measurements, not sure then why in BeerSmith, the estimated pre-boil gravity is lower than the post-boil gravity in my recipe, I'll just have to keep that in consideration for future reference.

Your pre-boil SG is lower because as you boil and evaporate water, the sugar content becomes more concentrated resulting in a higher gravity post-boil.

Is it normal that the differences in gravity from pre-boil to post-boil to be that different and why is that the case? I do a pretty vigorous boil, not sure if that has anything to do with it.

Yes, on average, my SG changes about 15 points from pre-boil to post. I.e.: Pre-boil SG: 1.045 and Post-Boil OG: 1.060

Yup, took the reading after collecting all the wort into the kettle.

The only other explanation for your post-boil reading to be lower than your pre-boil is that somehow more water got added in. Maybe a leaky wort chiller?

 

[TyHadaway]

The only other explanation for your post-boil reading to be lower than your pre-boil is that somehow more water got added in. Maybe a leaky wort chiller?

No leaks that I have picked up, I pump the wort through the coil in the HLT to sterilize it before adding any chilled water when cooling and there are no traces of leaks in the HLT or in the cooling water whilst chilling.

I think I will just put this down to a learning curve, I will brew the same recipe again using the same procedures and see what happens. I'm normally pretty good with documenting each brew, but I must have gotten distracted with something somewhere along the way. The only other thing I can come up with is that I might have had a temperature differentiation in the pre-boil and post-boil readings and might have been at two different temperatures and somehow jotted in the same temperature for each reading.

 

[chickypad]

I'm thinking maybe you didn't stir the wort well prior to taking your preboil gravity and got mostly first runnings. 1.072 would make sense as a first runnings gravity, but not as a preboil gravity for a 1.062 beer. I don't think you would have overshot that much.

 

[TyHadaway]

I'm thinking maybe you didn't stir the wort well prior to taking your preboil gravity and got mostly first runnings. 1.072 would make sense as a first runnings gravity, but not as a preboil gravity for a 1.062 beer. I don't think you would have overshot that much.

Come to think of it, I think you just hit the nail on the head. I don't recall giving the wort a stir after transferring to the boil kettle. Cheers.