Help - Not hitting post boil gravity

My equipment:

I have a 15gal Keggle boil kettle (5500watt heating element - I usually run the boil at 65% pwm) with a chugger pump, whirlpool arm, and a 30 plate wort chiller.

My Problem:

According to BeerSmith I was supposed to have 8.5gal pre boil volume at 1.040 pre boil SG. I collected about 8.75gal pre boil at 1.038 pre boil gravity (I figured the lower pre boil SG was on account for collecting .25gal more than BeerSmith said). After boiling for 60min, whirl pooling for 20min, then running the wort through the plate chiller back into the whilrpool for ~25min. My volume read 7gal which I thought was great since 1.5gal were lost to evaporation and .25gal loss to chill shrinkage. I collected about 6.5gal into the fermentor and checked the post boil gravity. It was 1.040!! BeerSmith calculated 6gal collected at 1.050! I missed the mark by 0.010!! which drove my brewhouse efficiency down to 66%!

My question is what am I doing wrong? My last couple batches barely changed from pre boil gravity to post boil gravity causing my beers to be wwwaaaayyy lighter than expected.

Any help would be appreciated. should I turn my pulse with modulation boil % up?

I also transfer the the wort from the mash tun to the boil through a paint strainer to help strain some of the gunk, but I use that same strainer as a jerry rigged hop spider.

 

What temperature are you measuring your gravity at?

the wort must be at 68 degrees for your hydrometer to read accurately.

Otherwise there must be an error in your volume measurements or beersmith inputs somewhere.

 

Well the pre boil was at 140F, But I use the Hydrometer tool on BeerSmith to correct the gravity reading.

 

Have to agree with this above. I don't see how you can have such a reduction in volume, but yet your gravity barely changed. Something is off in the calculations or temperature somewhere.

 

I keep checking and rechecking the settings on BeerSmith. Maybe my hydrometer is damaged/not working properly?

Can anyone tell me what their PWM % is set on their Auber PID for the boil?

 

The correction factor isn't terribly accurate and only works if it's within 20 degrees or so. It will still be waaaaay off with that big of a difference. I would bet money that's your problem right there.

You can check your hydrometer by putting it in room temp water. It should read 1.000

 

Thanks Mad King. So basically if my hydrometer reading isn't accurate at high temp, then my mash efficiency isn't as great as I had thought it was (beer smith said 86%) and my post boil gravity check would be more accurate.

Maybe I should just invest in a refractometer. I need to get a Ph/temp reader anyway. Anyone have any suggestions to brand?

 

So incase anyone else has this problem, I think I found part of the reason:

My equipment setup on Beer smith had a 1gal loss to trub and chiller which pushed the preboil volume up to ~8.5 gal. When actually I only loose about 0.5gal to trub. I reset that number to .5 and now Beersmith says my preboil volume should be ~8gal. I'm thinking that the extra .5-.75 gal was over sparging and caused the low gravity. The other part would be the faulty hydrometer. Just some of my thoughts

 

I dont mess with measuring my gravity going into my boil, because im not fixated on my gravity coming out. Not being a commercial brew house a minor fluctuation in batch to batch is part of the the enjoyment of home brewing. That said using the math, 1.038 - 38 points of gravity x 8.75 gallons pre / 6.5 gives you 1.051. I would check your hydrometer and trust your process.

 

Get a refractometer for quick reference checks.

 

Blasphemy!! What if you have to overcome efficiency loss by buying $.38 more grain!?! What world of disorderly madness do you brew in??

 

I buy base malt by the sack.and who is to say if you hit your target gravity you get uniform attenuation from the biggest variable in the whole magic trick.when I'm done it's beer and I drink it. That said I'm seldom under my target because I have refined my brew process.