Random (Bizzare) Efficiency Question

[NobleNewt]

I'm on my 3rd BIAB, but probably my 25th homebrew overall. I actually quit the hobby a few years ago and picked it back up with a far more condensed setup. I'm still dialing in my equipment, efficiencies, and processes, but I had a weird efficiency day on my Saturday brew sesh..

My estimated post-mash/pre-boil gravity was 1.039 and I measured 11 Brix on my refractometer (1.044) which is about what I expected based on my last brew session with the same equipment. (Last time, I was a little more efficient than BeerSmith said I would be and the same held true here as well.) Anyway..

I boil off about 1.15 gallons per hour which I took into account. After an hour boil, 2 ounces of hops, and leaving a little trub in the bottom of the kettle, I took a OG of 12.5 Brix (1.050) and got exactly my 3.5 gallons into the fermenter.

My question is this: If my expected pre-boil gravity was 1.039 and my expected SG was 1.053, that would leave a gain of 14 gravity points from boil-off. My actual numbers were 1.044 with a SG of 1.050 leaving only a 6 gravity point gain from my actual boil. So what was the deal?

With regard to the boil, I actually kept my lid on and cracked slightly. (I know, sound the DMS alarm now!) But my thinking was since I had a higher pre-boil gravity, I could limit my boil off, get a little more wort, and hit my SG number right on or even a little low. The fact of the matter is that I missed the SG a little low with the same amount of wort in the fermenter as I would have expected.

My pre-boil volume was spot on, I've calibrated my refractometer recently, and I know I didn't misread it, so is there any legitimate reason for the less-than-expected number of gravity points from the boil? Some piece of physics I'm wholly unaware? Black magic stealing my gravity points? Is Russia involved?

I'm really looking forward to this brew and I'm not even slightly worried about its outcome, I just want to know if there's any logical reason for the readings I got.

 

[wilserbrewer]

You need to provide a little more data...

Accurate pre and post boil volumes and gravities are needed.

Accurate volume measurements are needed or we be guesstimating...

My guess is you didn’t collect enough wort and boiled off less than anticipated to hit your target 3.5 gallons.

How much did you actually boil off?

Pre boil volume?
Post boil volume?

 

[NobleNewt]

You need to provide a little more data...

Accurate pre and post boil volumes and gravities are needed.

Accurate volume measurements are needed or we be guesstimating...

My guess is you didn’t collect enough wort and boiled off less than anticipated to hit your target 3.5 gallons.

How much did you actually boil off?

Pre boil volume?
Post boil volume?

Pre-boil was right at 5 gallons.
Post-boil was just a little under 4.

Unfortunately, I can't give you exacts since my kettle sits a little wonky on the burner outside. From the sightglass, though, it appeared that I boiled off what I expected to.. Appx. 1.15 gallons. For reference, I missed my volumes very badly on the previous batch, made the adjustments to my equipment in BeerSmith, and hit everything (volume-wise) much closer this time.

I also squeezed every ounce of wort out of that grain bag!

 

[McKnuckle]

1.039 pre-boil with 5 gallons gets you to 1.050 with 3.9 remaining in the kettle post-boil.

Unfortunately, refractometer readings are just not reliable in my experience. You really can’t multiply Brix by 4 and get any better than an approximation of SG. There is always the annoying “correction factor” which in my experience varies every time, making the device pretty much useless. It is particularly likely to over-state pre-boil due to evaporation of water on the refractometer glass and/or inadequate mixing.

I always measure OG and pre-boil with a hydrometer for this reason.

 

[NobleNewt]

1.039 pre-boil with 5 gallons gets you to 1.050 with 3.9 remaining in the kettle post-boil.

Unfortunately, refractometer readings are just not reliable in my experience. You really can’t multiply Brix by 4 and get any better than an approximation of SG. There is always the annoying “correction factor” which in my experience varies every time, making the device pretty much useless. It is particularly likely to over-state pre-boil due to evaporation and/or inadequate mixing.

I always measure OG and pre-boil with a hydrometer for this reason.

Thanks for the input.

I haven't had that experience with my refractometer, but at the same time I wouldn't be shocked if that were the case. When I was doing traditional all-grain brewing, I found that my refractometer was very accurate but that's just my experience. Next time, I'll take hydro readings as well and compare the two.

You've answered my question in the sense of "What variables could have caused these discrepancies?" That's all I really wanted to know.

In the end it'll be beer, and we'll all be happy.

 

[doug293cz]

There is a simple formula that relates pre-boil volume and SG to post-boil volume and OG:

Pre-Boil Vol * (Pre-Boil SG - 1) = Post-Boil Vol * (OG - 1)
​

To get 1.053 OG from 5.0 gal of pre-boil wort at 1.039 you would have to boil off:

Post-Boil Vol = 5.0 gal * 0.039 / 0.053 = 3.68 gal
​

In your case of 5 gal pre-boil @ 1.044, and an OG of 1.050, your post-boil volume needed to be:

Post-Boil Vol = 5.0 gal * 0.044 / 0.050 = 4.4 gal
​

Since you say your post-boil volume was a little under 4 gal, then one, or more, of your volume or SG measurements is in error.

Brew on

 

[NobleNewt]

There is a simple formula that relates pre-boil volume and SG to post-boil volume and OG:

Pre-Boil Vol * (Pre-Boil SG - 1) = Post-Boil Vol * (OG - 1)
​

To get 1.053 OG from 5.0 gal of pre-boil wort at 1.039 you would have to boil off:

Post-Boil Vol = 5.0 gal * 0.039 / 0.053 = 3.68 gal
​

In your case of 5 gal pre-boil @ 1.044, and an OG of 1.050, your post-boil volume needed to be:

Post-Boil Vol = 5.0 gal * 0.044 / 0.050 = 4.4 gal
​

Since you say your post-boil volume was a little under 4 gal, then one, or more, of your volume or SG measurements is in error.

Brew on

Thanks! I dig the formula.

By running some numbers, what I'm starting to think is that I mis-read my refractometer.

Probably read the wrong line and it was in fact 10 Brix (1.040) and my post-boil volume was slightly higher hence the slightly lower gravity. I've been known to mis-read that refractometer from time to time.

I feel pretty certain with my volumes.. They just couldn't have been off by that much. I hand-measured the mash water in with a pitcher and still got the right volume into the fermenter. Ipso facto my error was in reading my pre-boil gravity. Thanks for the help, though!

Sometimes even a dumble-doofus such as myself needs a little straightening out.

 

[fendersrule]

I know some people are going to kill me, but the refractometer in my experience isn't a "highly" accurate tool. It's "somewhat" accurate.

I find that the refractometer is an ideal tool for measuring change....so for souring it's AWESOME....or when you're adjusting sugar profiles for cider making.

But when you're trying to read SG or OG, I always find that it's +/- .003-.005, no matter how many times I calibrate it to something. .003 is good enough for me to give me an "idea", but it sounds like .003 is within your concern.

Hydrometers never lie. Refractometers can slightly lie.

Of course make sure you are giving your wort a good mix before drawing a sample.

Even with a refract, if you know how much total volume you have, and if you have an OG, you can easily calculator your efficiency. How much liquid did you end up with? Don't make it difficult!

Is your calculation of your expected OG with 3.5 gallons?

 

[fendersrule]

What size is your fermenter?

 

[balrog]

I wouldn't say hydrometers "never" lie. The paper can slip, for instance. You should always check. But I do have mixing, evaporative, reading, issues with refractometers but they get me close on preboil, and I always do both refractometer and hydrometer for OG anyway, and they've never been off by more than 1 SG point. This leads me to believe that measuring hot wort via refractometer is not absolute. So, for instance, you could use it to see if you're close; but you'd never want to use it in a patent application.

 

[NobleNewt]

What size is your fermenter?

5 gallon bucket!

 

[NobleNewt]

I wouldn't say hydrometers "never" lie. The paper can slip, for instance. You should always check. But I do have mixing, evaporative, reading, issues with refractometers but they get me close on preboil, and I always do both refractometer and hydrometer for OG anyway, and they've never been off by more than 1 SG point. This leads me to believe that measuring hot wort via refractometer is not absolute. So, for instance, you could use it to see if you're close; but you'd never want to use it in a patent application.

Yeah, I always give the sample an opportunity to cool and for the glass to adjust to the sudden change in temperature before I even take a look. Usually a few minutes while I'm getting ready for the boil or preparing the fermenter post-boil. Again, I've never had trouble with my refractometer being misleading, but then again it's tough to get an exact Brix measurement.. Much harder than a good hydrometer that is.

 

[NobleNewt]

I know some people are going to kill me, but the refractometer in my experience isn't a "highly" accurate tool. It's "somewhat" accurate.

I find that the refractometer is an ideal tool for measuring change....so for souring it's AWESOME....or when you're adjusting sugar profiles for cider making.

But when you're trying to read SG or OG, I always find that it's +/- .003-.005, no matter how many times I calibrate it to something. .003 is good enough for me to give me an "idea", but it sounds like .003 is within your concern.

Hydrometers never lie. Refractometers can slightly lie.

Of course make sure you are giving your wort a good mix before drawing a sample.

Even with a refract, if you know how much total volume you have, and if you have an OG, you can easily calculator your efficiency. How much liquid did you end up with? Don't make it difficult!

Is your calculation of your expected OG with 3.5 gallons?

Yeah, the expected calculation was with 3.5 gallons, and that's what I got into the fermenter. With that, my OG (refractometer conversion) was 1.050 with an expected OG of 1.053. By what you're saying, the +/- .003-.005 would put me almost on the number.

I wasn't at all worried about .003 gravity points, I just wanted to know where my error was in not gaining enough gravity points over the boil. But I chalked that up to a bad refractometer reading pre-boil.

 

[fendersrule]

You may be within measurement error.
Sometimes my refract and hydro are perfect sync, sometimes not!

Make sure you got a great crush going and continue onward!

Btw, I’d be putting near 5 gallons of wort in a 5 gallon bucket!

 

[doug293cz]

Yeah, I always give the sample an opportunity to cool and for the glass to adjust to the sudden change in temperature before I even take a look. Usually a few minutes while I'm getting ready for the boil or preparing the fermenter post-boil. Again, I've never had trouble with my refractometer being misleading, but then again it's tough to get an exact Brix measurement.. Much harder than a good hydrometer that is.

If you don't cool a small sample in a way that minimizes evaporation, you can get erroneously high Brix readings with a refractometer. I usually take a few oz and cool it in a covered container, and take a few drops for the refract from the larger sample. So far my refract has always been within about 0.0005 - 0.001 SG of my hydrometer readings (my refract has the "typical" 1.04 correction factor.)

Brew on

 

[NobleNewt]

You may be within measurement error.
Sometimes my refract and hydro are perfect sync, sometimes not!

Make sure you got a great crush going and continue onward!

Btw, I’d be putting near 5 gallons of wort in a 5 gallon bucket!

I have the LHBS crush my grain for me, then I run it through a Corona mill for good measure. My mash efficiency has been in the 80% neighborhood for each of the last two batches, so that's the least of my worries (even with a less-than-perfect refract reading).

I'd like to be able to put my 3.5 gallons in a 4 gallon fermenter, but it's an awkward volume and no one makes a 4 gallon bucket/fermenter that I've been able to find. I brew such an inbetween batch size because 3.5 gallons in the fermenter is the exact volume it takes to fill 24 16 oz. swing top bottles!

If you don't cool a small sample in a way that minimizes evaporation, you can get erroneously high Brix readings with a refractometer. I usually take a few oz and cool it in a covered container, and take a few drops for the refract from the larger sample. So far my refract has always been within about 0.0005 - 0.001 SG of my hydrometer readings (my refract has the "typical" 1.04 correction factor.)

Brew on

That's a really good point. I've never considered evaporation could alter that sample accuracy. I'll try your tactic next time as well as actually taking a hydro sample.

 

[fendersrule]

Good. Your efficiency is down pat!

There's just no difference in time it takes to make 3.5 gallon or 5 gallons of beer, so that's why I ask. Interesting that you're using your 16oz swing top bottle as a way to assess this....I'd move on to the 22-24oz swing tops (or just buy some) and move up to 5 so you don't have an awkward size batch! If you have a 5 gallon fermenter, use it all!

5 gallon fermenters hold 5 gallons of wort just fine and dandy....just have some large clean blow-off tubes and you'll get lots more beer that way, and you won't have to re-calculate every receipt you come across. Some 5 gallon fermenters actually hold more than 5 and leave more headspace for blow-off, so even better.

Just a tip and what I would do. I'm someone that makes 10 gallon batches, I only do 5 gallons if I'm experimenting. I've made enough beer now that even my "experiments" taste good enough to drink 5 gallons of!

 

[McKnuckle]

I actually have two stainless 4 gallon (16 qt) pails. They are a pet product. You can buy a glass lid with a rubber seal around the circumference and clamp it with binder clips. I even installed a rotating SS Brewtech pickup tube in one of mine.

https://www.statelinetack.com/item...n3QzmeOWVmwFlidYIdaG-tuKtRdmKh14aAvZ9EALw_wcB

 

[NobleNewt]

Good. Your efficiency is down pat!

There's just no difference in time it takes to make 3.5 gallon or 5 gallons of beer, so that's why I ask. Interesting that you're using your 16oz swing top bottle as a way to assess this....I'd move on to the 22-24oz swing tops (or just buy some) and move up to 5 so you don't have an awkward size batch! If you have a 5 gallon fermenter, use it all!

5 gallon fermenters hold 5 gallons of wort just fine and dandy....just have some large clean blow-off tubes and you'll get lots more beer that way, and you won't have to re-calculate every receipt you come across. Some 5 gallon fermenters actually hold more than 5 and leave more headspace for blow-off, so even better.

Just a tip and what I would do. I'm someone that makes 10 gallon batches, I only do 5 gallons if I'm experimenting. I've made enough beer now that even my "experiments" taste good enough to drink 5 gallons of!

Yeah, the efficiency thing got worked out in my 2nd (of 3) batches, so that was a win.

Before I stopped homebrewing the first time, I was doing 5 gallon all-grain with the whole shebang.. Kegging, keezer, DIY counter pressure filler, etc. This time around, I wanted the simplest setup possible plus I don't drink much anymore really. Maybe 4 pint beers on the weekends as a reward for fitness, so a 3.5 gallon batch (with my wife drinking a few) gets us nearly a month down the road.

I was of the same mentality as you, but BIAB is so much easier, less time consuming, and simpler than full-scale all-grain, so I really don't mind. I can have a batch finished from strike to chill in 4 hours and that's still doing a good bit of dilly-dallying. My first batch I was done in 3 hours with a SUPER slow chill.. I think I did a 30 minute mash and 30 minute boil, but I missed the leisure time of the longer mash and boil so I put that back into the routine. Plus, I usually use that time to catch up on my ghostwriting work.

Also, part of the delicate balance of wife appeasing was to A) limit the amount of alcohol in our home, B) keep the initial investment cost down, and C) not steal all of our weekend time for this hobby. So all of that factored into my batch sizing and setup. BUT if it were my way, we'd be doing 5 gallons with a kegerator!

I may consider expanding to do split batches or partigyle down the road, but BIAB will be the way I do that.

I actually have two stainless 4 gallon (16 qt) pails. They are a pet product. You can buy a glass lid with a rubber seal around the diameter and clamp it with binder clips. I even installed a rotating SS Brewtech pickup tube in one of mine.

https://www.statelinetack.com/item/indipets-heavy-duty-stainless-steel-dog-pail/404086 16QT/?srccode=GPSLT&gclid=Cj0KCQjws5HlBRDIARIsAOomqA3ywGpsNucqBYV8UgMdLarn3QzmeOWVmwFlidYIdaG-tuKtRdmKh14aAvZ9EALw_wcB

That's actually a really good idea! I've also considered getting some of these clear containers from the Webstaurant Store. You can get them in 3 or 4.5+ gallons with lids, and they're clear!

https://www.webstaurantstore.com/30...iners.html?filter=capacity:4~22-qt.:3-gallons

I use their brand for fermenting my sourdough bread.