Measured OG below Estimated OG

I just brewed an IPA with BIAB. Brewhouse efficiency was 80% which is exactly what I expected. Everything went great until the very end. The estimated OG for this recipe, according to BeerSmith 3 was 1.071. My measured OG was only 1.060. This is confusing to me since my measured pre-boil volume and gravity equaled the BeerSmith estimated pre-boil volume (8.58 gallon) and gravity (1.049). The target batch size was 5 gallon. 4.75 gallons actually made it from brew kettle to fermenter, so I only topped up with one quart of distilled water.

Is there any logical explanation for my OG being lower than expected? How significant is that difference? Will the FG be proportionately lower, leading to the same ABV?

Thanks.

Let's start with the last question first:  Your FG will be lower based upon the attenuation of the yeast you used active on a lower gravity.  There will be less residual sugars, dextrins, etc left in the fermented beer.

The difference is significant, but have no fear -- you did make beer!  The balance may be off a little bit between the malt and hops but without seeing the recipe, there is no way of determining (even with the recipe, it would be pure speculation) how it will come out.

So, hitting on the main issue, something is wrong with your brew house efficiency to end up that low in OG and yet short on volume.  Usually, in order to have a low gravity versus target, the volume must be over target in order to achieve the same BHE as the recipe was designed.  Without seeing the rest of your process and numbers, it is hard to speculate too much,  It would probably be easier if you exported the recipes as a .bsmx file and posted it so we can all look at the recipe, achieved numbers vs target numbers, etc.

Thanks for your reply. Like you, I don't completely understand what is going on. I have attached the bsmx file and hope it sheds some light on it for you. Then, maybe you can help my understand how to fix this.

Thanks, Adrian

On the subject of topping off... you are only diluting and already lower than expected beer. You need to decide which is more important to you: achieving the volume you want but the beer lower in ABV. Or - keeping the ABV closer to the target and having a little less product. I always go with the second choice.

One thing you can do to reach your target OG is to keep some DME on hand.

Just keep brewing and take accurate notes so that you can correct problems the next go round.

Maybe I need to describe this better. After mashing, my pre-boil volume was high and SG lower than expected. So, I boiled off the excess volume and then remeasured gravity. It was almost perfect, 1.049 compared to estimated 1.050. I then started my boil and hop additions. After the boil, my volume was also high, not surprising considering how humid it was yesterday. So, I again boiled off the excess to reach expected post-boil volume. I cooled the wort and transferred it to my fermenter. The result was 1 quart less than expected, so I added that volume, assuming that the OG would actually be too high, otherwise. Obviously, I was wrong.

I suppose I could have checked the OG before topping-off, and I suppose I will do that from now on. However, I still don't understand how my OG was so low after adding only 1 quart of water, pre-boil volume and gravity being essentially perfect (after additional boiling, as above), and boiling off until I reached the expected post-boil volume. The math does not seem to make sense to me.

Also, you are not recommending adding DME after the wort has cooled, if the OG is lower than expected, are you? Wouldn't this be a potential source of contamination if the DME is not boiled?

OK, so starting with your wort collection, you are greatly off in you volumes through the process.  You boiled off extra wort, but the program does not necessarily know this.  Given this, the actual efficiencies as BeerSmith calculates them are suspect.

Start by getting a handle on your volumes.  If you are constantly adjusting your boil off or needing to add water, the program cannot calculate the targets based upon your current equipment profile.

Take the measurement of water you started with (mash + sparge) and subtract the amount of wort you collected.  This difference is any dead space in your mash tun and the grain absorption for that particular malt bill.  If you have set up your equipment profile previously, you probably measured any dead space in your mash tun and can subtract this value from the volume difference.  If you did BIAB in your boil kettle, then your dead space should be set to zero and the measured difference is your grain absorption.  Divide this volume difference by the amount of grain.  Convert the units to get oz of water per oz of grain and you can update the grain absorption constant in the program which can be found under 'options' > 'advanced'

Next, your pre-boil volume minus your post boil volume becomes the amount of water boiled off during the total time period of your boil.  This number divided by the number of hours in your boil becomes your boil off rate.  You can update your equipment profile with this number. 

If you had any trub left over after filling you fermenter, you can update the equipment profile with this value.

These changes should bring your mash water volume and post boil volumes closer to your actual results.

One big thing that is often overlooked when figuring out your efficiency numbers is the care which you measure your gravity readings.  Are you using a refractometer or hydrometer to get your gravity readings?

If a refractometer, make sure you stir the wort well and take a minimum of 3 readings, cleaning off the refractometer well between readings.  Dried sugars on the surface of the prism or on the refraction cover will skew your readings quite a bit.  Also, check your refractometer against distilled water before you start.  This will tell you if you have any residue or if your calibration is off before you even begin.

If you are using a hydrometer, always - always - always chill your wort sample to either the calibration temperature of your hydrometer (found on the paper scale inside the hydrometer) or at least close enough to room temperature.  Trying to take a reading on a hot wort sample is like trying to measure the height of a falling snowflake.  You have to catch everything at just the right time with the right information to get a answer which may be close to what the answer actually is.  Everything you do to the hot wort (insert thermometer, hydrometer, handle cylinder) as well as ambient conditions (air flow, room temp vs wort temp) is causing a change in that wort's temperature which can throw off your 'corrected' reading.

Unfortunately, I have not had a chance to go through your recipe file as I have been working straight since yesterday morning and will be traveling all weekend, but I think you explanation of your brew day helps a lot in defining what the issues may be.

Somehow I was under the impression your OG was low and that you discovered that during the boil. That is why I suggested having some DME on hand...to add during the boil to correct for lower than expected gravity.

To expand on Oginme's explanation of measuring volumes here is a video that will help demonstrate what he describes.

https://www.youtube.com/watch?v=HwEbjOt8OR8

An accurate and customized equipment profile is essential to get the most out of the software.

Kevin58 said:

Somehow I was under the impression your OG was low and that you discovered that during the boil. That is why I suggested having some DME on hand...to add during the boil to correct for lower than expected gravity.

Click to expand...

Thanks, Kevin58!  I forgot to address that issue.

DME is very useful to have on hand for low OG corrections.  One way to utilize it is to put a small pan on the stove with the dme needed to bring the OG closer to your target and then add judt enough water to get it into solution.  Boil it for about 10 to 15 minutes and it will be sanitized enough to add into the fermenter.

Thank both of you for your suggestions. I think the grain absorption correction will help considerably as I am using BIAB. It does make complete sense that BeerSmith cannot calculate volumes with the additional boiling off I had to do. I have not had consistency in my technique so far. So, I have been adjusting my volumes in BeerSmith with subsequent brews. Hopefully, I will get more consistent. Meanwhile, if I end up with higher volumes and lower SG than expected, I figure it is better to boil off the excess water than have a dilute wort.

As for measuring SG, I use both a digital refractometer and a hydrometer whenever the wort is hot. I want to trust the refractometer, since I can use it when the wort is hot, but I'm just not confident in its correlation to SG. So, I confirm the reading by letting the hydrometer wort cool to room temp before reading from it. For OG, I just use the hydrometer, since the liquid is already cool.

Boiling DME in a small amount of water is also a good idea.

By the way, I am a physician and have done enough lab work with fluids to make myself annoying (and compulsive) with this. I'm also an avid cook, so I know how recipes and individual steps can influence the end product.

I really do appreciate your suggestions.