93% efficiency??

[LukeB]

Hi everyone!

Yesterday, I tried my first BIAB batch. The process seemed to go fine...easier than I thought...but I got a huge reading from my pre-pitch gravity measurement. I only have a 5 gallon kettle, so this was my process for a 3 gallon batch:

I mashed 6.75lbs of grain (6lbs 2-row, 0.75lbs Crystal 60) for 60 minutes in 3.25 gallons of ~158 degree water (I wanted 153, but it didn't cool down much when I added the grain). I pulled the bag up and fly sparged with 1 gallon of ~170 degree water and squeezed the bag "firmly", but not crazy hard.

At this point, I had around 4 gallons of wort which is exactly what I wanted. I did a pre-boil hydrometer reading which came out at 1.052 after adjusting for temperature. I thought that was pretty high, but I'm new at this, so I just went with it.

After the boil, I had three gallons just as I wanted and, after cooling the wort, I took another hydrometer reading and got 1.077. I thought that must be wrong as my target was 1.058, so I measured it again and got the same result. Plugging the numbers into this Brewhouse Efficiency calculator, I got an efficiency of 93%! The fermentation is going like crazy, so it seems like that may be right.

My question is, how did this happen? Did I do something wrong? I figured mashing mistakes would lead to low efficiency, but can mistakes lead to really high efficiency?

 

[mattd2]

...At this point, I had around 4 gallons of wort which is exactly what I wanted. I did a pre-boil hydrometer reading which came out at 1.052 after adjusting for temperature. I thought that was pretty high, but I'm new at this, so I just went with it.

After the boil, I had three gallons just as I wanted and, after cooling the wort, I took another hydrometer reading and got 1.077.

I am going to guess you have made a mistake measuring somewhere since if you boil down 4 gallons of 1.052 wort to 3 gallons you should have 1.069 wort.
What temps were you taking the sg measurements at, as the adjustment for temps above/below the calibration point don't work well when you are to far away from it.

 

[Sammy86]

I use this calculator when measuring preboil and post boil gravity

http://www.brewersfriend.com/hydrometer-temp/

Personally, I'm going to stop doing the preboil Gravity because of the time it takes to put the sample in the freezer wait for it to come to temp and then take a reading.

IMHO, the starting gravity (post-boil) and final gravity are the most important ones to take note of.

Cheers!

 

[LukeB]

I am going to guess you have made a mistake measuring somewhere since if you boil down 4 gallons of 1.052 wort to 3 gallons you should have 1.069 wort.
What temps were you taking the sg measurements at, as the adjustment for temps above/below the calibration point don't work well when you are to far away from it.

The pre-boil measurement was done hot...125 degrees according to my notes. The measurement was 1.042 which I plugged into the Brewer's Friend adjuster and got 1.052. So that's probably the issue, then. The post-boil measurement was done at 80 degrees (adjusted with the same calculator), and I did that one twice, so I feel pretty confident about it.

 

[jtratcliff]

Personally, I'm going to stop doing the preboil Gravity because of the time it takes to put the sample in the freezer wait for it to come to temp and then take a reading.
Cheers!

Why? It's not like you have to stop everything and wait for your pre-boil gravity before you can continue on...

Just pop the sample in the fridge and keep going. Come back to it whenever you have time.

It can be a useful data point.

 

[doug293cz]

Your 93% efficiency is possible with the amount of grain and water you used. In order to get that, your conversion efficiency had to be essentially 100%, as your theoretical maximum lauter efficiency is about 93%. Your pre-boil gravity should have come in at 1.056.

Good job on the mash.

Brew on

 

[pcqypcqy]

Why? It's not like you have to stop everything and wait for your pre-boil gravity before you can continue on...

Just pop the sample in the fridge and keep going. Come back to it whenever you have time.

It can be a useful data point.

I don't even bother with the fridge, I just take the sample and get on with my boil and usually towards the end it's cooled sufficiently. I leave the hyrdometer in there just to see how it changes with temp. After I've noted it, I jam my thermometer in there quickly to note the temp and do the calculation later.

 

[Sammy86]

Why? It's not like you have to stop everything and wait for your pre-boil gravity before you can continue on...

Just pop the sample in the fridge and keep going. Come back to it whenever you have time.

It can be a useful data point.

Valid point...I just never seem to hit my preboil estimated gravity and then like many novice Brewers worry about it until I take the post boil gravity which I've hit my post boil gravity.

Yes, it is useful I don't disagree but it's not essential IMO.

 

[TexasWine]

Valid point...I just never seem to hit my preboil estimated gravity and then like many novice Brewers worry about it until I take the post boil gravity which I've hit my post boil gravity.

Yes, it is useful I don't disagree but it's not essential IMO.

Don't mean to beat a dead horse, but if you're missing your preboil but hitting your post boil, then I would say something is most likely wrong with the assumption you've made for boil off rate. Either that or your preboil reading is consistently wrong some how.

Fix the problem and then you'll be able to make adjustments should you ever truly miss your numbers. Data can be a powerful tool.

 

[Gnomebrewer]

I've hit over 105% efficiency on my last 3 brews.....


turns out my kitchen scales were dodgy.......

 

[Hello]

Don't mean to beat a dead horse, but if you're missing your preboil but hitting your post boil, then I would say something is most likely wrong with the assumption you've made for boil off rate. Either that or your preboil reading is consistently wrong some how.

Fix the problem and then you'll be able to make adjustments should you ever truly miss your numbers. Data can be a powerful tool.

I agree with this. Also, buy a refractometer with ATC. No waiting for anything to cool.

 

[mattd2]

I've hit over 105% efficiency on my last 3 brews.....


turns out my kitchen scales were dodgy.......

I've done a similar thing... except my kinda lousy eff end up to be a terrible eff!

 

[Komodo]

Use a refractometer. You can grab quick gravity measurements preboil, which is useful to know exactly how long to boil given your volume - which is critical for knowing when your hop schedule starts. The tiny sample you pull off is essentially insta-cooled when you put it on the plate. You can also check during the boil which I find helpful as boil off rates change depending on pot geometry, weather, or if the lid is on or off. Boiling off DMS precursors comes to mind here.

 

[LukeB]

Your 93% efficiency is possible with the amount of grain and water you used. In order to get that, your conversion efficiency had to be essentially 100%, as your theoretical maximum lauter efficiency is about 93%. Your pre-boil gravity should have come in at 1.056.

Good job on the mash.

Brew on

Thanks...I guess I'm just concerned about how to predict future batches. Is the efficiency of my brew setup and/or technique something I just have to learn from experience, or is there a way to predict it?

 

[doug293cz]

Thanks...I guess I'm just concerned about how to predict future batches. Is the efficiency of my brew setup and/or technique something I just have to learn from experience, or is there a way to predict it?

For a batch sparge process, it is possible to predict efficiency with good accuracy if you know your typical apparent grain absorption (in gal/lb or L/kg), mash tun undrainable volume (zero for BIAB), strike and sparge water volumes, and grain bill with associated gravity potentials. These numbers are used to calculate the lauter efficiency (what percentage of the sugar created in the mash gets into the BK.) The other factor in mash efficiency is the conversion efficiency (what percentage of the potential sugar in the grain actually gets created in the mash.)

Mash Efficiency = Conversion Efficiency * Lauter Efficiency​

It is possible to monitor the progress of conversion in a mash by checking the SG as the mash progresses. From the grain bill and strike water volume you can calculate the maximum possible SG for the wort in the mash. So conversion efficiency is just (Wort SG - 1) / (Max Wort SG -1). So when the SG reaches the max possible, the conversion is complete. Since there are likely to be small errors in the grain potentials, the calculated max SG might be off, so that the final SG of a completed mash might be a little higher or lower than predicted. So in practice, conversion is complete when the SG stops increasing with longer times. You can also check for mash completion with an iodine test (just be sure to sample the grain as well as the wort, and crush up the grain particles to expose unconverted starch.)

In order for the lauter efficiency calculations to be accurate, it is necessary for the sugar concentration to be uniform throughout the mash, both during initial run off and sparge run offs. This can be accomplished by aggressive stirring prior to run off. So, then if you monitor your mash for conversion completion you know you are at (or very close to) 100% conversion efficiency, and the mash efficiency just becomes the lauter efficiency.

With fly sparging it is much more difficult to predict lauter efficiency, as the rinsing is a dynamic process rather than an equilibrium process. Modeling a fly sparge process will involve setting up and solving differential equations, and determining a bunch of equipment dependent calibration constants.

When I ran a sanity check on your numbers, I just assumed that you did a 1 gal batch sparge instead of a 1 gal fly sparge. Since most of your sugar came from the initial run off, I figured the error in my estimate would be small. My calculated lauter efficiency for your batch was 93% which says your conversion was 100%.

Brew on