Low Pre-boil gravity

[slamback]

For my past several AG batches I've come in way under my pre-boil gravity. So I've tried to bring it up by boiling a little bit longer, then I end up over-shooting the OG after boil. I am mashing in a 10 gallon igloo maxcool cooler with braided coil, and batch sparging. I'm mashing with 1.5 qts/lb of grain but it seems like i'm not getting as much wort as I should from that first running. Then I sparge until I get to 6.5 gallons, & I must be diluting it too much. But then I can't figure why I'm over after the boil - maybe I overcorrected too much?

Example - last batch I was making a Rye Pale Ale, my pre-boil gravity was supposed to be something like 1.053, and I came in at 1.044. I boiled for 80 minutes, then my OG was 1.064. BeerAlchemy told me it should be something like 1.059.

I know it's probably not the end of the world, but I'm confused as to why this might be happening. Any thoughts?

 

[MalFet]

It could be your math, or it could be that your 1st and 2nd running aren't fully mixed when you take your gravity reading.

What were your volumes at each of these steps? 6.5gal of 1.044, presumably, but how much liquid did you end up with?

 

[slamback]

I definitely would not trust my math, but I do tend to trust my computer's math... After boil (and spilling some on the driveway when transferring to carboy) I ended up with about 4.75 gallons in the carboy. Also I did stir it before the boil, but perhaps not enough.

 

[MalFet]

I definitely would not trust my math, but I do tend to trust my computer's math... After boil (and spilling some on the driveway when transferring to carboy) I ended up with about 4.75 gallons in the carboy. Also I did stir it before the boil, but perhaps not enough.

You may trust the computer's math, but if you don't fully understand what it is doing you won't know if you're using it wrong.

6.5 gallons of 1.044 is 286 points, and 4.75 gallons of 1.064 is 304 points. Those 18 points only account for a 5% margin of error or so, which ain't much...especially if your volume measurements aren't precise.

Most likely what's happening is that you don't have BeerAlchemy configured properly for your evaporation rate, etc. Those projections only work if your pre-boil and post-boil volumes accurate match what your software is expecting.

 

[ajf]

When I was setting up Promash, I had it set to boil off at 14% per hour.
I changed it to select gallons per hour, but forgot to change the 14%
Imagine my surprise the next time I used it, when it told me I needed a pre-boil volume of ~20 gallons for a 5 gallon batch.

-a

 

[akimbo78]

i assume you are correcting your gravity for temperature?

 

[slamback]

Yes, I am correcting for temp. I definitely think you are correct in saying the beer alchemy is not set up right. Its the first time I've brewed with it, that's got to be the problem. I guess I shouldn't trust the computer's math after all thanks y'all

 

[ArrowheadAles]

Do you have a refractometer? I usually check mine often with that during the lauter and boil to make sure I hut my numbers as close as possible. Also, worse case scenario, if you end up waaay under gravity its good to have some liquid extract on hand to bump it up a few points if you need.

 

[slamback]

I don't have a refractometer, I've heard mixed reviews - I don't want to spend the money on something that is unreliable. You would recommend it?

 

[periwinkle1239]

I don't have a refractometer, I've heard mixed reviews - I don't want to spend the money on something that is unreliable. You would recommend it?

I highly recommend a refractometer myself. It has really come in handy. It's awesome to be able to take measurements not only of your run-offs but while you're boiling as well. It also makes me feel more like an actual chemist

I haven't noticed any unreliable readings. Every now and then I take back to back measurements just take make sure they are accurate.

This is the one I have: http://www.northernbrewer.com/shop/brix-specific-gravity-refractometer-w-atc.html

 

[slamback]

Looks like a good one, it certainly would make things easier. Now to convince SWMBO that I should spring for one... uh maybe next year... Thanks!

 

[Kayos]

I've been using a $25 ebay one for the last 3 years. I like how much less wort it takes to use more than anything. The key is to use some RO water and dial it into 0 for calibration the first time.