Brewzilla 4 boiloff rate question

[Frisp]

folks. following the last brew numbers being all over the place i did a boiloff test on my 35L bz4 .

20 L of cold water took just over an hour to come to the boil at full power with the lid off..
30 min rolling boil at 102C with lid off and then chilled with the IC back down to 20C

I measured what was left ,17.2L, which gives an hourly boil off rate as 5.6L/hr

that seems massive to me ???
am I missing something here??

 

[The Baron]

did you have the heat on full if so that is why you had so much boil off. I turn my heat down to about 60/65% once boil is reached for a slight rolling boil instead of a intense one

 

[Frisp]

did you have the heat on full if so that is why you had so much boil off. I turn my heat down to about 60/65% once boil is reached for a slight rolling boil instead of a intense one

I was watching the boil , which I did outside, and even with the heat jacket in place it didnt look overly vigorous. as boils go. it was struggling to hit 102C and a lot of the time was sat at 101.
but then again in teh past I have always liked a vigorous rolling boil

I think Ill redo the test first chance I get and try as you suggest knocking the power back a bit.

 

[The Baron]

I boil at the garage door with it open and struggle to get to 101c unless I have it on full but in my opinion a do not need a heavy rolling boil and that's why I knock my power down as long as it is a boil it is ok for me.
I do not measure absolute nowadays but I would say mine is between 3.5 and 4 ltrs per hour on a low rolling boil so 5.6 on a full power seems possible

 

[Frisp]

Thinking is a dangerous thing..
IF i use set boiloff rate @ 4l/hr in brewfather and it actually boils off @5.6L an hr
I should be able to use the post boil gravity to calculate and dilute the wort back to my target OG after the boil ?

if my thinking is right Id then be able to make adjustments after each brew to get my boiloff rate dialed in.

 

[The Baron]

I sometimes boil off too much and just adjust the amount in Brewers Friend recipe calculator to my volume or you can change it to your required OG by adding water or sometimes if it is short add a little sugar.
Playing with the recipe inputs will tell you how much sugar or water to add etc

 

[Frisp]

I sometimes boil off too much and just adjust the amount in Brewers Friend recipe calculator to my volume or you can change it to your required OG by adding water or sometimes if it is short add a little sugar.
Playing with the recipe inputs will tell you how much sugar or water to add etc

Excellent. thats what I was thinking.

 

[foxy]

Thinking is a dangerous thing..
IF i use set boiloff rate @ 4l/hr in brewfather and it actually boils off @5.6L an hr
I should be able to use the post boil gravity to calculate and dilute the wort back to my target OG after the boil ?

if my thinking is right Id then be able to make adjustments after each brew to get my boiloff rate dialed in.

Good idea, a boil off under 4 litres means you aren't boiling like you mean it. 4 litres is a good place to start.

 

[RoomWithABrew]

Don't forget you brought to boil with lid off and boiled with lid off and ? cooled with lid off.
Evaporation is occurring at all temps above freezing ( at standard pressure ) just gets quicker as it gets hotter.

Repeat your experiment but collect relevant data.
No need to boil at 100% either.

 

[Frisp]

Don't forget you brought to boil with lid off and boiled with lid off and ? cooled with lid off.

hmmm good point.. the evaporation rate would be different following a mash wi the lid on, then bring to the boil lid on, then boil lid with off .

So really I need to collect real time data during a brewday rather than just boil 20L of water. and make any gravity adjuastments post boil until I get the boiloff rate dialed in..

 

[foxy]

hmmm good point.. the evaporation rate would be different following a mash wi the lid on, then bring to the boil lid on, then boil lid with off .

So really I need to collect real time data during a brewday rather than just boil 20L of water. and make any gravity adjuastments post boil until I get the boiloff rate dialed in..

No need to go as far as that, boil say 10 litres for half hour then double the loss.

 

[Agentgonzo]

that seems massive to me ???

Yes, that's massive. 5-10% boil off per hour is a ballpark to aim for. Above that (unless you're trying to condense the wort for a strong beer) is just wasting energy and even damaging the wort

 

[RoomWithABrew]

hmmm good point..

So really I need to collect real time data during a brewday rather than just boil 20L of water. and make any gravity adjuastments post boil until I get the boiloff rate dialed in..

A much better way of collecting data and as others have said you can liquor back if too strong or just accept it's more sessionable and drink a bit more.
Adjust one or two variables each brew and you'll soon dial in.

 

[jambop]

Well just because they say 3L per hour does not make it so. Boil off will vary from day to day and also for altitude to altitude. My water boils at 99C but a high pressure day is going to change that a little. I have a dedicated brewhouse so I have to open a small window and use a large fan to evacuate the water vapour my boil off is around 4L per hour most brew days .