Hitting pre boil gravity but low OG

[TacoGuthrie]

My last few brews I've been having this problem where I come up about 6-8 pts short on my OG. Yet when I do a pre-boil gravity check I hit it dead on according to my Beersmith print out.

Can someone help me trouble shoot this one? I thought it might be boil off but I'm boiling it down to 6 Gallons, similar to what I've done for over a year and I haven't changed my equipment or setup in a while.

I also thought it might be because i was pulling the wort from my spiggot, which is on the bottom of my pot and so I thought i might be getting my first runnings. However last time I stirred well and scooped my wort from the top of my pot and the same thing happened.

any other ideas?

 

[northernlad]

Your calculations or measurementss are wrong. Gravity is linear. [email protected] gallons is 6 gallons @1.0625. Period.

 

[theonetrueruss]

Could it be a problem with the temp that the pre boil wort was measured?

 

[TacoGuthrie]

I definitely get the pre boil sample below 100 and usually get it to 70 or so. Regardless, I use this adjustment tool.

northernlad the calculations are made by beersmith. I'm confident in my gravity measurements.

I'm brewing this morning and will be extra careful with all my measurements and report back.

 

[TacoGuthrie]

Okay I totally need help here.

On my brew today, according to Beersmith my pre-boil gravity is supposed to be 1.042. And my estimated OG is 1.052. This is at 75% efficiency.

I collected 6.75 Gal of wort and measured my pre-boil gravity at 1.044. Great, right??

I boiled for 1 hour. The recipe is for 5.5 gallons. After an hour I'm only at 6 gallons but i don't want to keep going because i've put in my aroma hop additions at 10 adn 5 and was about to put in an oz at 0.

So I haven't boiled off as much as Beersmith thinks i should have. I will have to adjust this because my OG is only 1.048.

Plus when i do some calculations by hand it seems like i only boiled off .58 of a gallon.

44 * 6.75 / 48 = 6.18

So what can i do to improve my brew day? I figure i get a more vigourous boil going and adjust my boil off rate in beersmith to get more realistic numbers.

 

[BendBrewer]

Yeah that isn't much boil off. Sounds like a weak boil.

I lose 1.5 gallons during an hour and gain 6 points on 11 gallon batches.

 

[SmokeShank]

Your not boiling with lid on are you? Stupid question I know. I found the beersmith had my boil off volume to high and I was way over on my o.g and added water afterwards.

 

[TacoGuthrie]

Today i didn't boil with the lid on but sometimes i have it half on. I brew outside and sometimes the elements would blow into the pot if i didn't cover it.

I think i need to find a video of a 'vigorous boil'.

 

[BendBrewer]

http://www.youtube.com/watch?v=rm5NN7WIqrk

 

[northernlad]

I definitely get the pre boil sample below 100 and usually get it to 70 or so. Regardless, I use this adjustment tool.

northernlad the calculations are made by beersmith. I'm confident in my gravity measurements.

I'm brewing this morning and will be extra careful with all my measurements and report back.

I am not trying to be a dick about this but...
Beersmith's calculations are right, YOUR calculations and/or measurements are not.
Example: If you have 10 gallons of 1.050 wort, you WILL have 8 gallons of 1.0625 or 5 gallons of 1.100. There is nothing that can change that. If you regularly hit your preboil gravity, stop taking an OG.

As far as your last brew day, there is enough margin for error in your volume measurements and your gravity readings to account for the negligible difference in your numbers.

I think you just need to trust one or the other of your numbers and let it go.

 

[ThePearsonFam]

I'd be inclined to agree with a few of the previous posts.

1) the gravity is a function of volume. a small change in the volume can significantly influence the gravity of your beer. I have marks on my spoon and labels on my carboys to estimate the volume of beer but even that's a rough measurement of the volume. make marks on your fermenter to get a more accurate measurement (if you haven't already done so).
2) I too have a bigger boil-off rate. BS is defaulted too low for my setup. I also adjusted my loss to trub a bit since I use a keggle. I left the shrinkage (I think 4%) alone since that's a function of the water and temperature. my total loss during the boil/transfer to fermenter process is ~ 1.5gal for a 60 minute boil.
3) slightly off topic, but, remember to keep the pot uncovered enough that the steam can freely flow out to prevent DMS formation.

 

[TacoGuthrie]

http://www.youtube.com/watch?v=rm5NN7WIqrk

This is helpful thanks. And thanks to the other suggestions too.

• Adjust the vigour of my boil
• boil with the lid off
• set up beersmith to account for trub
• double check the volume marks on my brew stick