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Low Pre Boil Gravity

I just tried my first all grain. According to Beer Smith, with a mash temp of 150F with a steep time of 75 minutes, I should have had a pre boil gravity around 1.039. After a fly sparging, I ended up with a low per boil gravity of 1.023 and post boil OG of 1.034.

I'm looking what I could have done wrong so I can correct it next batch. Thanks

7.5lb Pale 2 row
0.75 Crafa II
0.5 Roasted Barley

I’m probably not the one to diagnose your problem. However, those that are will probably want many more details about how the grain was crushed, your fly-sparge setup, your post-boil wort volume, etc.

What was your final volume? You’re only .005 points low which makes me think you may have ended with slightly more than 5 gallons (or whatever the volume of the kit)

Either that or your efficiency is lower than 75%. Hard to say why, could several things. Possibly the crush?

Could be a measuring device issue. Did you use a hydrometer? Or a refractometer? Be sure to take the reading when the wort is cool, 60F. Are they calibrated? Should be reading 1.000 in distiller water

Sadly, I messed up the volume as well and I was way under the target volume. I marked my kettle at 6.5 gallons for 20% loss durring and 60 minute boil. Then I noticed the Beer Smith instructions said it should be 5.7 gallons. So I guessed the amount based on my previous markings on my boil kettle. This is to say I was way shy of my target. My final volume is more like 4 to 4.5 gallons.

My mash tun is an igloo cooler and my fly sparge method was just pouring 170 deg water through a strainer while moving the strainer back and forth across the cooler.

I measured my gravity with a auto temp correcting refractometer that shows brix and gravity.


I see. Well it looks like your efficiency was really low then, this could be because of the crush wasn’t fine enough, your pH, dough balls in the mash, channels in the mash

Also a possibility of incorrectly weighed grain.

It’s hard to say… How fine was your crush? Did you crush yourself? Sorry Im not much help, it’s tough to diagnose these types of things

I bought the grain crushed form Norther Brewer and it only sat for two weeks so don’t think that was it. (BTV ROCKS!) If I was to guess. I would think:

  1. my stainless braided hose is too long and thus being suspended near the surface so more water and less sugar is filtering through.

  2. Dough balls

  3. maybe my drain rate was too high not giving the water enough contact time with the sugar while sparging

This batch is fermenting well so maybe it will be a good session beer? Either way, I’ll try another one this weekend.

1st item would be the crush. HBS don’t want to crush to much and have people complain about stuck sparges.

By your handle, I’ll assume you don’t live near the store and you are having items shipped to you? You could see if they will double crush them. A couple pounds of DME on hand can help you with last minute adjustments.

Being low on your volume and low on the OG shows something is really wrong. The low volume should have raised you OG.

If after a a couple more brews your OG’s are still way low, you can add another pound or two of 2row to get the OG right.

2 pieces of advice from me:

1: shorten your braid. Maybe add a SS bolt to the end to add some weight to it.

2: Try a batch sparge with your next batch.

I would also suggest batch sparging if you have the space in your tun. I use a 10 gallon cooler for 5 gallon batches which lets me do a batch sparge of adding all the sparge water to the mash when it’s finished mashing then let it sit for 10 minutes essentially a mash out. This is nice for me because of the set it up and let it run after the vorlauf. Adjust the draining rate to prevent channeling and let it drain, about an hour for me.

Just make sure you hit your temps, pH and get a solid idea of your volumes.

Awesome advice everyone. I think I have a game plan for the weekend. I’ll post a follow up.

Oh and one other thing only way to get better at brewing is to brew often and ensure you have homebrew on hand while brewing that’s the real trick my wife likes to have parties with co workers and it usually cleans out a keg of my brew. Happy Brewing sir and cheers.


I measured my gravity with a auto temp correcting refractometer that shows brix and gravity.


What was the temp of the wort when you checked it they only correct temp up to a certain deg I think mine is only accurate up to 90 degs. The instructions that came with yours should tell the max temp it will compensate for.

Good call Chuck!

I had to do some digging to find the model number but it is the REF113 with a ATC range of 50 to 86 deg F ( 10-30C ).That would make the real gravity a bit higher I would suspect. I would think a drop or two of wort would cool pretty quickly but I’ll have to remember that from now on.

After this posing and a bunch of research, I found I did a bunch wrong while fly sparging. Not the least of which was a way to fast a run off.

Well I took the day off to brew. Thanks to all the advice, this one came out exactly on target. Pre boil was 1.052 for 6.5 gallons and OG for 5 gallons with was1.062 as Beer smith said it should be for my IPA recipe.

Thanks again for all the advice.

Congrats! BTW - a lot of us batch spate and run off pretty fast. Check out for insight from one of the best!!

I have the same mash tun, and although I’m still new to AG brewing, I’ve gotten good efficientcy thus far. I batch sparge and run the first running as quickly as my system allows (per Denny who posts here often). I also do the same with my second running. This summer, my first brew (speckled heifer) was spot on. My second (Single hoped best bitter) was 1.050 instead of the suggested 1.045, so I was somewhat higher.

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