Boil-off Rate as a percentage ??

[The-Engineer-That-Brews]

It inexplicably annoys me that BeerSmith, which is very good in most other respects, insists on specifying boil-off rate as a percentage per hour.

This is just plain stupid. If it were true then you would never be able to boil a kettle dry.

The rate at which the boiling wort in your copper gets converted to steam depends one thing and one thing only: the net rate at which energy is supplied to it - i.e. (typically) the electrical power going into your heating element, minus any losses from the walls of the copper.

So unless you're reducing the power as the copper gets emptier (unlikely) then your boil-off rate will be a fixed number of litres per hour.

Rant over!!

 

[The Baron]

I would think the surface area of the kettle would have some impact of all results too?

 

[The-Engineer-That-Brews]

I would think the surface area of the kettle would have some impact of all results too?

Intuitively yes, but in fact no :-)
It's literally the rate of energy supply (in kilowatts = kilo Joules per second) divided by the latent heat of vaporisation of water (2,260 kilo Joules per kilogram) - surface area doesn't come into it, (correction: except as a source of heat loss due to evaporation...)

Okay, yes you're right to say that surface area has an effect - but actually a lot less than you'd imagine. The power of the heater is the main factor I think :hat:

 

[The-Engineer-That-Brews]

Actually one thing that does effect the boil-off rate is whether you keep the lid partly on during the boil… it doesn’t change how much steam is produced per minute, but it does mean that a certain proportion of it condenses and drips back into the pot.

 

[RoomWithABrew]

Correct, my system with lid and condenser on only has a boil off of 0.7litres per hour and that's at 25% power.

 

[nickjdavis]

My copy of Beersmith specifies boil off as an hourly rate in litres per hour.....not as a percentage. Not sure where you are seeing a percentage (I'm on version 3.2.7)

 

[foxy]

The diameter plays a part in the amount of boil off, I have a 60 litre SVB and a 40 litre SVB I lose 4 litres on my 40 litre and 5 on the 60 litre which has the bigger surface area.
But to predict a boil off is nigh impossible, always better to work that out for oneself.

 

[Eskdale]

What I was taught was, 'Boil like you mean it'. There is a host of things happening in the boil, so skimping on energy can also lead to skimping on quality.
Things to be mindful of, be sure the DMS is getting stripped out, the DMSP needs to be converted at a high temperature, malt with a higher DMSP will need a higher evaporation rate than a malt with a lower DMSP.
DMS is only one of a number of volatile's which needs to be removed, what is vital in the boil is the coagulation and precipitation of proteins, as well as the maillard reaction which adds colour and flavour to beer.
Finally when boiling the wort there will be a drop in pH as the calcium continues to precipitate, ideally the pH value should end up between 5 and 5.2.

Emma

 

[The-Engineer-That-Brews]

My copy of Beersmith specifies boil off as an hourly rate in litres per hour.....not as a percentage. Not sure where you are seeing a percentage (I'm on version 3.2.7)

Actually you're right Nick - if I go into the Equipment Profile editor it's litres per hour; but in the 'vols' tab of the recipes it comes up as a percentage ... and what's more, it calls it an 'evaporation rate' - which it isn't. Evaporation and boiling are very different processes (but now I'm ranting again... LoL)

 

[chthon]

Actually one thing that does effect the boil-off rate is whether you keep the lid partly on during the boil… it doesn’t change how much steam is produced per minute, but it does mean that a certain proportion of it condenses and drips back into the pot.

Only until the lid gets heated up to 100° C. Depends a bit on the energy put in of course, with a lighter boil this effect will probably be less.

 

[chthon]

Correct, my system with lid and condenser on only has a boil off of 0.7litres per hour and that's at 25% power.

But here you are not only using a lid, but also a condenser. The condenser is made to reduce losses. Also, you seem to the boiling at a quarter of your power, so that also reduces the boil off.

 

[chthon]

The diameter plays a part in the amount of boil off, I have a 60 litre SVB and a 40 litre SVB I lose 4 litres on my 40 litre and 5 on the 60 litre which has the bigger surface area.
But to predict a boil off is nigh impossible, always better to work that out for oneself.

Do you use a different amount of power to get their boil going and then sustaining?

 

[Sadfield]

This is just plain stupid. If it were true then you would never be able to boil a kettle dry.

If you boiled your kettle dry over an hour the evaporation rate would be 100%.

If you boiled dry over two hours the evaporation rate would be 50%/hour. Losing 50% of the total volume per hour, not depleting the volume by 50% each hour.


It's an indication of rate of volatilisation that works over all systems. L/h doesn't, as losing 2L/h on a 20L kit is vastly different than an on a 1000L kit. To remove dms, Crisp recommended a boil off rate of 6% minimum for a 60 minute boil.

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

 

[foxy]

Do you use a different amount of power to get their boil going and then sustaining?

No same power to get a really good aggressive boil going.

 

[RoomWithABrew]

@chthon
I think the condenser is designed to condense the evaporated liquid, so that you don't have steam everywhere.

With a lid and condenser on because more heat is retained if you boil at 100% you'll get far too vigorous a boil and boilovers. Hence you turn it down.
If your wort is boiling it's boiling, more energy will not raise the temperature any more. Boiling point is fixed to pressure, people brewing at altitude can still drive off dms when their wort boils at a lower temperature.
A more vigorous boil might drive the volatiles off quicker but not necessarily any more effectively.
I do go to the boil point at full power and then dial power back.

 

[Eskdale]

From what I have read I think the steam condenser in a home brew perspective is more of a gimmick to sell to the home brewer.
A good read here a brewery will expect a boil off rate of above 4% stated here an average of 7% our average as home brewers would be around 15%.

Emma
https://static1.squarespace.com/sta...1780ee8f4d/1589305346117/Steam+Condensers.pdf

 

[The Baron]

@chthon
I think the condenser is designed to condense the evaporated liquid, so that you don't have steam everywhere.

With a lid and condenser on because more heat is retained if you boil at 100% you'll get far too vigorous a boil and boilovers. Hence you turn it down.
If your wort is boiling it's boiling, more energy will not raise the temperature any more. Boiling point is fixed to pressure, people brewing at altitude can still drive off dms when their wort boils at a lower temperature.
A more vigorous boil might drive the volatiles off quicker but not necessarily any more effectively.
I do go to the boil point at full power and then dial power back.

I never boil at full power I dial mine down as you can get a good enough boil without Vesuvius erupting I also do it for another reason as I have read that using a all in one bonded heating element it can shorten the element life by using it on full power for long periods

 

[RoomWithABrew]

From what I have read I think the steam condenser in a home brew perspective is more of a gimmick to sell to the home brewer.
A good read here a brewery will expect a boil off rate of above 4% stated here an average of 7% our average as home brewers would be around 15%.

Emma
https://static1.squarespace.com/sta...1780ee8f4d/1589305346117/Steam+Condensers.pdf

You are right it is a gimmick that condenses the evaporate so that you don't get condensation on the walls, ceiling etc. I don't see that it changes the laws of physics in my locale.
Your boil off will condense somewhere whether its one percent or twenty percent. Extraction systems get condensation in the pipe work unless the pipe work is very hot or very short.

 

[The Baron]

Now now Gentlemen lets not get into rubbishing each others beers. In defense of CC he does put out some excellent recipes for other members to try and you may not realise that head retention in the UK is a thing of debate as in the North they generally like a head but in the South it has been served with minimum/none head for years

 

[Chippy_Tea]

The Baron asked you to stop you ignored him so i have deleted 9 post which must be a record for a thread outside the Snug!