Calculating boil-off

[Twostage]

I'd like to be accurate with boil-off so I know if the pre-boil SG is right or not. I've been fiddling with the brewday settings in the recipe app but its guesswork.

I'm thinking of sticking 10 litres of water in the boiler and running it for an hour an measuring it, would that be accurate with it not having sugar in it ?

 

[Galena]

I think that's the recommended method, that's how I always do it with a new kettle. Then compare it when you do a brew and adjust as necessary.

 

[dreaddan]

That was the recommended way when I started.
The bit I wasn't sure of is tye measument was hot last or cold.

 

[Twostage]

That was the recommended way when I started.
The bit I wasn't sure of is tye measument was hot last or cold.

I'm going to assume that nothing (or nothing significant) is lost getting to the boil and then measure as soon as it's cooled off a bit.

Now wondering if there is something I could do with c. 8 litres of boiled water.

Doing it this morning.

 

[MashBag]

I'm thinking of sticking 10 litres of water in the boiler and running it for an hour an measuring it, would that be accurate with it not having sugar in it ?

No.
Different voltages.
Different humidity not too mention different sugar concentrations will all vary the boil off.
And different software

Why not just adjust and correct in the fv?

 

[Twostage]

No.
Different voltages.
Different humidity not too mention different sugar concentrations will all vary the boil off.
And different software

Why not just adjust and correct in the fv?

Good question. All but one of my FVs don't have graduations so I don't know what volume I am diluting from (or adding sugar to). Another thing I'm going to fix by marking out measuring sticks I can put up against them to approximate volume.

I'm only looking for approximates so I can be closer with the recipes and better prepared on the day. My last brew had pre and post SGs of 1.026 and 1.052. I could have chilled it faster and had more beer by diluting

 

[MashBag]

Yeah. I am all about easy brew days.

Calibrate that one fermentation vessel and you are good to go. I measure the 23L of water in, mark it, and then use it for the brew next day.

 

[obscure]

Good question. All but one of my FVs don't have graduations so I don't know what volume I am diluting from (or adding sugar to). Another thing I'm going to fix by marking out measuring sticks I can put up against them to approximate volume.

I'm only looking for approximates so I can be closer with the recipes and better prepared on the day. My last brew had pre and post SGs of 1.026 and 1.052. I could have chilled it faster and had more beer by diluting

With regards to checking volumes in unmarked vessels I use a set of bathroom scales, a litre of wort is going to be roughly a kilo.

 

[Sadfield]

Another way to approach it is to control the temperature applied to the wort to achieve the best boil.

Evaporation Rate % = ((post-boil volume or gravity/pre-boil volume or gravity)-1)*100

Aim to achieve around 6% evaporation over 1 hour (recommended by Crisp Malts). Enough to remove volatiles, but not damage proteins in the wort or cause fowling.

An easy way to measure boil volume is to make a dip or ullage stick for your kettle. Measure your preboil volume, then calculate the 6% evaporation volume to aim for. Or monitor SG with a refractometer.

Going off the FV volume will be adding in other losses, such as kettle dead space, shrinkage in cooling, loss to trub and hop absorption. And won't give a true indication of evaporation.

 

[MashBag]

Going off the FV volume will be adding in other losses, such as kettle dead space, shrinkage in cooling, loss to trub and hop absorption. And won't give a true indication of evaporation.

Which is exactly why it is better. You don't need to bother with evap rate at all.

 

[Twostage]

Did the test - 10 litres went down to 6.4. 36% boiloff . I'm assuming it would be less for larger volumes of a sugar solution.

It's a burco cygnet and I just leave it on max with the lid partially off. When I brewed before I sometimes set it less than that but I was never happy with the stop start boil. I also built one of those triac voltage controllers but I was constantly wary of it.

I'm thinking put up with stop/start, lid more on but don't fret it.

Forgot to make the graduated dip stick

Anyway, at least now I some info that I can use.

 

[Sadfield]

Which is exactly why it is better. You don't need to bother with evap rate at all.

Sure, if you ignore the rest of the post and don't care about wort quality.

 

[MashBag]

Let's stop there. That's just is just incorrect and you know it.

There room in brewing for different folks and different methods.

 

[Sadfield]

There room in brewing for different folks and different methods.

Which is exactly why it is better. You don't need to bother with evap rate at all.

The hypocrisy.

Let's stop there. That's just is just incorrect and you know it.

There's plenty of papers documenting thermal stress on wort, which can be measured and monitored using the thiobarbituric acid index. Even on a simple scale, scorching can have a detrimental effect on wort quality.

https://www.homebrewtalk.com/threads/boil-vigor-and-thermal-stress.673058/

 

[Birdsnestbrewery]

Did the test - 10 litres went down to 6.4. 36% boiloff . I'm assuming it would be less for larger volumes of a sugar solution.

It's a burco cygnet and I just leave it on max with the lid partially off. When I brewed before I sometimes set it less than that but I was never happy with the stop start boil. I also built one of those triac voltage controllers but I was constantly wary of it.

I'm thinking put up with stop/start, lid more on but don't fret it.

Forgot to make the graduated dip stick

Anyway, at least now I some info that I can use.

My understanding is that it's a more-or-less fixed volume of boil-off per hour.,rather than a percentage of volume. I would imagine it's related more to the top surface area than volume.
I find that I lose about 3l per hour on mine on full blast, but I intend to build a pwm controller to reduce the intensity of the boil.

 

[bobukbrewer]

If the boiler is cylidrical with constant diameter then volume equals 3.14159 times diameter squared divided by 4 times height of water, and height can be measured from the top (say height is 2 ft 6 ins, and top to water surface is 9 inches giving depth of water = 1 foot 9 ins). Make a table of say top to water from 3 ins to 24 ins and calculate the volumes...........

 

[Twostage]

My understanding is that it's a more-or-less fixed volume of boil-off per hour.,rather than a percentage of volume. I would imagine it's related more to the top surface area than volume.
I find that I lose about 3l per hour on mine on full blast, but I intend to build a pwm controller to reduce the intensity of the boil.

I built one of those. From memory it buzzed and got hot (despite the cooler thing bolted to it ) and I was never happy I could leave it and go and do something else so I stopped using it. Could be me being a big girl's blouse. I'd be interested how you get on.

 

[Twostage]

If the boiler is cylidrical with constant diameter then volume equals 3.14159 times diameter squared divided by 4 times height of water, and height can be measured from the top (say height is 2 ft 6 ins, and top to water surface is 9 inches giving depth of water = 1 foot 9 ins). Make a table of say top to water from 3 ins to 24 ins and calculate the volumes...........

I did something like that to work out a scale for one of my pots.

The pot had a 30cm diameter so pi r squared gives you roughly 707 so each centimeter of height gives you .707 of a litre. 1/.707 gives you 1.41 so a litre takes 1.41 centimeters. I've marked off a piece of slat to that scale and used that to work out the volume by holding it against the outside of the pot.

Going to do one for the cygnet.