trouble determining boil off rate - proposed workaround

[mwill07]

I have had trouble determining my boil-off rate for pretty much forever. sometimes I have too much wort at the end of the boil, resulting in too low gravity. sometimes I have too little wort, resulting in too low final volume (i.e. fewer servings).

My proposed work-around is to reduce the pre-boil volume from 6.5 gallons to 5.5 gallons, resulting in a post-boil volume somewhere lower than the desired 5 gallons. This reduced volume will allow me to top up as needed to exactly hit the desired final volume in the fermenter.

Partial boil would have a few other benefits:

• reduced time to reach boil
• reduced time to chill to pitch temp, especially if top-up water is chilled
• less likely to have boil-over

Questions:

1. anyone have any other practical tips for determining/controlling boil-off rate?
2. anyone else do partial boils to control volumes?
3. what will be the flavor impact? Seeing as how this isn't a 2.5 gallon partial boil, I'm thinking the impact is negligible but I'm open to discussion.

Thanks!

 

[runningweird]

boil off rate depends on what equipment you are using, a larger surface area leads to a larger amount of evaporation, a harder boil leads to more liquid evaporating.

1. your solution seems really complicated. why not just make a wort stick? -

fill your pot with 1 gallon of water - then insert stick(i always used a wooden dowel rod) and use something to mark the 1 gallon mark.

fill with second gallon of water - add stick - mark stick

continue until you have filled your pot and marked your stick.

then when you are boiling, insert your stick to get a relatively accurate measurement of where your volume is hanging out.

2. you can do smaller boils - it doesn't really impact flavor as long as you don't scorch your wort and add clean water afterwards.
3. I did partial boils a long time ago because I didn't have a pot capable of doing full boils

 

[mwill07]

boil off rate depends on what equipment you are using, a larger surface area leads to a larger amount of evaporation, a harder boil leads to more liquid evaporating.

1. your solution seems really complicated. why not just make a wort stick? -

fill your pot with 1 gallon of water - then insert stick(i always used a wooden dowel rod) and use something to mark the 1 gallon mark.

fill with second gallon of water - add stick - mark stick

continue until you have filled your pot and marked your stick.

then when you are boiling, insert your stick to get a relatively accurate measurement of where your volume is hanging out.

2. you can do smaller boils - it doesn't really impact flavor as long as you don't scorch your wort and add clean water afterwards.
3. I did partial boils a long time ago because I didn't have a pot capable of doing full boils

I've done the wort stick, didn't really care for it. I like to be precise in my measurements and don't really find the increments to be all that precise - I'd like to be better than +/- 1/4 gallon, and that seems to be the best resolution you can get with a stick like this.

I've also used a metal ruler where I could measure more precisely , and come up with the calibration - i.e. 20" = 5 gallons, 21"=5.5 gallons (or whatever) to come up with better resolution, but in the end I abandoned this whole effort because I don't really care to have my face that close to boiling liquid trying to take a measurement, especially when the liquid is splashing around.

 

[eluterio]

Questions:

1. anyone have any other practical tips for determining/controlling boil-off rate?
2. anyone else do partial boils to control volumes?
3. what will be the flavor impact? Seeing as how this isn't a 2.5 gallon partial boil, I'm thinking the impact is negligible but I'm open to discussion.

Thanks!

Answer 1) See what your temp hits at boil. I know at sea level boil happens at 212 F. Where I live its 3000ft and boils at 208 F. If you boil aggressively, meaning boiling is at 208 and you boil at 212 or above this will effect your wort amount. thus, your boil off will be greater.

2)Its called the Maillard Effect when you boil longer and affects flavor wikipedia has a great explanation. Easy explanation it could caramelize you wort some might not be horrible to have when you brew harder and longer or just harder. I wouldnt be too concerned about this.

I used a sitck at one point. I hated using wooden dowels because you cant sanitize it. I bough a sight glass and took care of the amount problem for me.

Hope this helps.

 

[Grannyknot]

I don't like the wort stick either.

To figure out my boil off, losses, etc..
I used brewing buckets with the gallon marks on the sides (Check to make sure they are accurate).
I sparged into the bucket, so I can measure each run-off (I end up with 8.5 gallons of pre-boil wort).
I boiled, then filled my fermenter and noted how much was in there, then dumped all my trub loss from my kettle to a bucket and took note of the loss (I usually have 1.25 gallons of trub loss).

My typical measurements are:
8.5 gallons pre-boil
2 gallons boiled off
1.25 gallons of trub loss
5.25 into the fermenter
5 into the keg

 

[eluterio]

One last thing to note, once you get your boiling down brew at min 5 times and you can get a good reading on what loss you will have.

 

[elatowski]

A refactometer is a great tool for measure gravity while boiling. Periodic checks during the later stages of the boil will let you know when you've reached your target gravity. For $25 shipped, I think it's a great and inexpensive way to get peace of mind.

 

[mwill07]

One last thing to note, once you get your boiling down brew at min 5 times and you can get a good reading on what loss you will have.

you know what, that's probably part of the problem. I do a really good job of measuring what goes into the kettle, but i'm not really measuring very precisely what I end up with. Frankly, by the end of the brew-day, I'm tired and just want to get it over with.

I know my last batch was way off because when I went to fill my keg post-fermentation, the keg overflowed and there was about 1/2 gallon still in the carboy. Obviously i had too much in the carboy to start with. By my records, my pre-boil volume was 6.25 gallons, but I have no idea exactly how much ended up going into the carboy.

 

[mwill07]

A refactometer is a great tool for measure gravity while boiling. Periodic checks during the later stages of the boil will let you know when you've reached your target gravity. For $25 shipped, I think it's a great and inexpensive way to get peace of mind.

so basically, you boil until target gravity is reached, volume be damned? interesting.

 

[elatowski]

but I have no idea exactly how much ended up going into the carboy.

Marking the outside of the carboys with some gorilla tape at gallon increments would solve that problem.

 

[rxpx40]

We've recently started all-grain brewing. We have converted a keg into our brew kettle. As many of you, we cut the top out of this keg. I haven't added any sight glasses or valves yet, we are still doing this Neanderthal style. I imagine several folks around here with kegs as brew kettles know exactly what their boil-off rate is. So, I don't feel like wasting 5 batches of beer to gain an understanding of what my boil off is. I am just above sea level in the wonderful metropolis of Austin, Texas. I think I'm brewing at just about 580'. Close enough for government work. Last batch called for 5 gallons to mash (17 lbs grain) and 5 gallons to sparge. I calculate a gallon lost to wetting the grain and another half gallon remaining in the MLT unrecoverable. That started me with too much to boil off in an hour, so we extended our boil.

But not until we'd already stuck to the original hop schedule.

So, when it came time to rack this batch to the dry-hop carbouy I tasted it.
It delivered one wicked harsh hop bomb. I sure hope it mellows out with age.
I did!:rockin:

Chris

 

[elatowski]

so basically, you boil until target gravity is reached, volume be damned? interesting.

I haven't quite determined which is the worse of the two evils. Having less of a beer made according to the numbers or having more of a slightly different beer than what you intended.

 

[stpug]

I feel your pain on the boil-off rate. I also deal with a variable boil-off rate and my situation is fairly consistent so there shouldn't be much to affect the rate. Regardless, when it comes to a big late hopped IPA, there's not much you can do but finish your boil according to recipe otherwise those late hops start moving in isomerization time.

I find a wort measuring stick to be pretty useless after I've reached preboil volume. I can't measure boiling liquid; it's hard to determine displacement with an immersion chiller in your pot; and then I need to account for the shrinkage from hot wort to cold wort. Like I said, pretty useless after I've used it to reach my preboil; HOWEVER, it's invaluable to that effect.

I think the best way to minimize your boil-off rate variability is to control your variables as best you can. Use the same boil pot. Measure your preboil precisely. Boil at the same setting on your burner/stove every time. Work in the same general environment every time (hot vs cold air temperatures affect boil-off too; as does humid vs non-humid environments). The idea is to minimize the variability in your boil-rate so you can predict the outcome better; otherwise you'll have to work within a vacuum if you want perfection every time .

In the end, maybe you end up with an extra 6-pack of 5.8% pale ale instead of 6%, or vice-versa. It's only beer and you will make more

 

[mwill07]

I feel your pain on the boil-off rate. I also deal with a variable boil-off rate and my situation is fairly consistent so there shouldn't be much to affect the rate. Regardless, when it comes to a big late hopped IPA, there's not much you can do but finish your boil according to recipe otherwise those late hops start moving in isomerization time.

I find a wort measuring stick to be pretty useless after I've reached preboil volume. I can't measure boiling liquid; it's hard to determine displacement with an immersion chiller in your pot; and then I need to account for the shrinkage from hot wort to cold wort. Like I said, pretty useless after I've used it to reach my preboil; HOWEVER, it's invaluable to that effect.

I think the best way to minimize your boil-off rate variability is to control your variables as best you can. Use the same boil pot. Measure your preboil precisely. Boil at the same setting on your burner/stove every time. Work in the same general environment every time (hot vs cold air temperatures affect boil-off too; as does humid vs non-humid environments). The idea is to minimize the variability in your boil-rate so you can predict the outcome better; otherwise you'll have to work within a vacuum if you want perfection every time .

In the end, maybe you end up with an extra 6-pack of 5.8% pale ale instead of 6%, or vice-versa. It's only beer and you will make more

so here are the parameters I use:

1. same kettle every time.
2. kettle goes on same turkey fryer on the same spot on my patio every time.
3. the lid stays off of the kettle.

However, I can't guarantee I'm pushing the same amount of BTU's into the kettle, I can't adjust for ambient temp, I can't adjust for humidity, and I can't adjust for wind.

I do measure the pre-boil fairly accurately - within a 1/2 cup for sure. I have a set of 1 gallon jugs that I sparge directly into, and then I dump these into the kettle. If I can't fill the jug completely, I dump into a large 1 qt measuring cup so I can record exactly how much wort goes in.... this is the amount of resolution I would like to see post-boil as well.

 

[mwill07]

I haven't quite determined which is the worse of the two evils. Having less of a beer made according to the numbers or having more of a slightly different beer than what you intended.

I suppose, like everything else, the answer is "it depends".

If it's house-beer, go for volume. If it's for competition, go for accuracy...right?

 

[duboman]

I sparge directly into the kettle and use a very well calibrated brew stick to measure to the quarter gallon. When I reach my required pre boil volume I'm good to go.

I brew outside and have no control over ambient anything as well but I do control my burner to get a nice rolling boil. My regulator has marks on it that I use to ensure I'm at the Same spot each time. I lose 1.85 gallons per hour, I know it's a lot but it is consistent.

If you are careful it's not impossible to be consistent. That being said, many commercial breweries do exactly what you propose. Boil to above desired OG and top off to needed OG. Keep in mind though that this process too has it's own variables to monitor, also not guaranteeing desired volume precisely if you're off

The refractometer is great as you can begin taking readings towards the end of the boil and make adjustments as you finish

 

[eluterio]

I suppose, like everything else, the answer is "it depends".

If it's house-beer, go for volume. If it's for competition, go for accuracy...right?

Simple reply would be YUP.

 

[eluterio]

you know what, that's probably part of the problem. I do a really good job of measuring what goes into the kettle, but i'm not really measuring very precisely what I end up with. Frankly, by the end of the brew-day, I'm tired and just want to get it over with.

I know my last batch was way off because when I went to fill my keg post-fermentation, the keg overflowed and there was about 1/2 gallon still in the carboy. Obviously i had too much in the carboy to start with. By my records, my pre-boil volume was 6.25 gallons, but I have no idea exactly how much ended up going into the carboy.

I agree with being tired at the end of the day. I made a spread sheet for my mash with temp and what time and refrac reading all the way to boiling and amount of water I use to sparge and temp and some other things so i can follow a regimen to achieve my consistency. Its a pain in the ass but after brewing 5 times I figured out why I was missing my marks here and water volumes there why I ended up with 6 gallons instead of 4. Again up front it was a lot of work but to me was worth it.

I have all my equipment marked on how many gallons it hold up to max. Its a pain again but well worth it. As soon as you have one filled its easier to calibrate new equipment.

 

[CA_Mouse]

Easiest way to determine the chiller displacement is to measure out your typical volume of wort, add your chiller and measure again. This will give you the amount of liquid that is displaced by the chiller. Also, remember that heated liquid displaces a higher volume of space than chilled liquid. You can find this out by measuring 2 gallons in your kettle with cold water, put the lid on it then bring it up in temperature and measure it again. This shows you the expansion due to heating. Chilling it and measuring it will show you the contraction you will experience with chilling your wort. If you aren't interested in getting these measurements, you won't get accurate information for future brews. If you want to repeat a specific brew that turns out great, having these numbers will help you re-brew the same beer repeatedly. The reasons people drink the same beer over and over (be it BMC, Sam Adams, or their local brew pub), is because they expect the beer to be the same every time they have it. Being able to repeat a brew is what makes a great brewer.

 

[mwill07]

thanks to everyone for the replies. Thinking on this a bit, I clearly need to do a better job of calibrating my equipment so I can better predict boil off rate. This requires I do a better job of measuring the volume of post-boil wort, and I expect it will likely take a few batches to get the process down pat.

Further, I need to mark my propane regulator such that I am consistently adding the same amount of heat. I don't know how accurately I can regulate this, but anything to try to make this as repeatable would be worthwhile. Certainly, this would be a compelling reason to go to an electric burner system - in my mind, that should be easier to be consistent with.

Until I can get my equipment better dialed in, I will continue as planned previously - that is, undershoot the desired pre-boil volume, under the premise that I can always add more water after the boil but can't take water out.

 

[MikeInMKE]

I made a spread sheet for my mash with temp and what time and refrac reading all the way to boiling and amount of water I use to sparge and temp and some other things so i can follow a regimen to achieve my consistency.

I just recently started measuring the pre-boil volume and gravity with a refractometer, and given a target post-boil volume calculating what the resulting post boil gravity would be at that post-boil volume.

Stating the obvious, the only thing you are boiling off is water. So if I'm starting with 7.5 gallons at 1.055, and I want 6.5 gallons at the end of a 60 minute boil:

7.5 * 55 = 6.5 * X
X = (7.5 * 55) / 6.5
X = 63.46, so the post boil gravity I'm shooting for is 1.063. At that gravity, I should have 6.5 gallons.

I want to go from 1.055 to 1.063, a change of 0.008 over 60 minutes. So every 15 minutes, the gravity should go up by 0.002. If it goes up by more than that, I add a little water. If it goes up less than that, I turn the burner up a little.

One thing I learned the hard way the first two times I've used this method is that the ATC on my refractometer is crap. I've learned it's important to cool the sample and make sure no solids are on the glass. Even then, it's not always easy to get a sharp line.

I've also started lifting the immersion coil out of the pot right at flameout so I can see what the sight glass says.

 

[Conan]

My boil off changes drastically from summer to winter. I'm at 13.5% in summer and upwards of 16% in winter. Even just dry days will alter the rate, but based on the season it's within my final volume tolerance. This is with a 14.5" wide kettle with a substantial surface area, though.

One thing you could try for your propane regulator is using a ball valve. Mount it directly to the burner (using reducers and couplings to the orifice). Turn the regulator to open and adjust the flame with the ball. It works for NG, anyway, and is really much easier to make fine adjustments, consistently. Kyle

 

[mwill07]

My boil off changes drastically from summer to winter. I'm at 13.5% in summer and upwards of 16% in winter. Even just dry days will alter the rate, but based on the season it's within my final volume tolerance. This is with a 14.5" wide kettle with a substantial surface area, though.

One thing you could try for your propane regulator is using a ball valve. Mount it directly to the burner (using reducers and couplings to the orifice). Turn the regulator to open and adjust the flame with the ball. It works for NG, anyway, and is really much easier to make fine adjustments, consistently. Kyle

That's a fair amount of variation - 3.5% difference over 6 gallons is roughly a quart of water...pretty significant, IMO.

As far as the ball-valve - good idea, but I don't think I'm comfortable with plumbing propane lines.

 

[Conan]

I took a few shots of my gas plumbing. It's not complicated at all, and a little teflon tape will seal the system. Since this is all downstream of your regulator you're only running at a couple psi, if that. Anyway, I don't mean to badger you into it so on with the pics:

That's the overall setup. Gray line is my NG supply, which goes in to the ball valve with a reducing bushing. Ball valve has another bushing on the 'out' end, which the orifice threads into. The orifice then threads in to the burner.

This is a closeup of the above setup.

The steel line on the left is the original orifice for my propane setup. That's what threads in to the burner, and the ballvalve/ reducer threads onto.

Yes, my boiloff changes quite a bit but most of that is my kettle diameter. Also, I brew in my driveway which is between my house and my neighbors, creating a little wind tunnel. It's rather breezy back there. Kyle

 

[mwill07]

so I brewed a batch yesterday, but took more time to better calibrate my equipment and note exactly what I was doing, and found some pretty big errors in volume measurements. What I had been doing is measuring the mash water by filling up gallon carboys, and I had been filling them up to the neck. Well, before doing that yesterday I took my wifes quart measuring cup and poured in exactly 4 quarts into each jug and marked exactly where one gallon was on each jug...it was a lot less than I had thought. a gallon comes up to about the shoulder of the jug, not the neck.

What I thought previously was a gallon was more like a gallon + 2 cups. So, what I thought was 6 gallons was really 6.75 gallons. No wonder there was too much left in the boil afterwards!

also, I better marked my carboy so I know what I have post-boil. Using the same calibrated jugs and quart measuring bowl, I marked each gallon up to 5 gallons and then single cup increments after that up to 7 gallons. I feel much better about knowing what I have post-boil now.

As it turned out, my boil off rate was only 6 cups/hour (0.375 gal/hr) - much lower than I had assumed.

So between me inaccurately adding too-much water and then the boil-off being much lower than anticipated, it's no wonder my beer has been a bit watery lately.

 

[stpug]

so I brewed a batch yesterday, but took more time to better calibrate my equipment and note exactly what I was doing, and found some pretty big errors in volume measurements. What I had been doing is measuring the mash water by filling up gallon carboys, and I had been filling them up to the neck. Well, before doing that yesterday I took my wifes quart measuring cup and poured in exactly 4 quarts into each jug and marked exactly where one gallon was on each jug...it was a lot less than I had thought. a gallon comes up to about the shoulder of the jug, not the neck.

What I thought previously was a gallon was more like a gallon + 2 cups. So, what I thought was 6 gallons was really 6.75 gallons. No wonder there was too much left in the boil afterwards!

also, I better marked my carboy so I know what I have post-boil. Using the same calibrated jugs and quart measuring bowl, I marked each gallon up to 5 gallons and then single cup increments after that up to 7 gallons. I feel much better about knowing what I have post-boil now.

As it turned out, my boil off rate was only 6 cups/hour (0.375 gal/hr) - much lower than I had assumed.

So between me inaccurately adding too-much water and then the boil-off being much lower than anticipated, it's no wonder my beer has been a bit watery lately.

Very good of you on double-checking your volumes. I suspect many more folks would benefit from a thorough double-checking of their system volumes/losses to get a more predictable end result. Your example is an excellent scenario for people to read to see how quickly things can get "out of whack" when you're not precise on your volume/weight/loss measurements.

Cheers!! Hopefully you'll give an update on your final outcome after brewing your next batch to see how much more closely you match the predicted final outcome.