Dumbass Question On Boiling

[SG9090]

Ok im a bit confused on the boil, how is boiling rate calculated.

I boil in a 65l S/S pot if i brew a single batch i have a evaporation rate of 20%. Yesterday a did a double batch. So i had 55L in pot expecting to boil down to around 44l after one hour, however after one hour i still had 49l in the pot.

How do i manage a double batch boil? do i just assume i have 20% evaporation on a single batch and 11% on a double batch


Cheers,

Shane

 

[SG9090]

One more question, What effect would this have on the bitterness profile?

 

[asis]

Your boil off in litres/hour will be the same for a single or double.

How many litres do you normally boil off?

 

[ekul]

Evaporation rate is dependant on two things, the surface area of the evaporating surface (most important) and the intensity of the boil.
The 20% figure is given as a rough estimate but really you will have to work out how much your system loses yourself, which you have just done. So next time start with 50L and hopefully you will end up with 44L.
Because the evaporation rate is the same providing the intensity of the boil stays the same you will always lose the same amount per hour. So you have lost 6L/hr. If you did a 80L batch you would need to start with 86L.

The longer boiling can affect your bitterness if you have lots of late hops. If you only have a bittering addition it will be slightly more bitter, but not by much, you probably won't even taste it. When i first started AG and was working out my volume calculations i would regularly be under gravity and have to boil for longer. If its only a bittering addition it doesn't matter, if you have late hops the brew will be way more bitter.

What i've started doing to make the end volume every time is to use cube hopping. So i make my brew up and throw in bittering hops. If at the end of my 60min boil i am under gravity (which doesn't happen all that much but it does sometimes) then i can boil it for a little longer without affecting the bitterness all that mauch. Once everything is right i drain the wort into the cube which contains my flavour/aroma hops. I calculate the cube addition as a 20min addition for bitterness, but the flavour and aroma taastes much higher than that.
Good luck mate.

 

[QldKev]

As the other ppl have said the boil will remain the same in L/hr, if you have the same size opening and same heat level.

When calculating the boil off rates for volume use the basis of L per Hour.

So a single, double, what ever in the the same pot should give off roughly the same litres of evaporation.

You only ever convert the boil off value from L/hr to a % to see if you are in range of your boil effectiveness. You should target 10 to 15%. (If you have a weird shaped pot this % may vary)

So your double 55L to 49L = 11% within range
Your single 27.5L to 22L = 20%, you could back the boil off a bit
My Single 29L to 25L = 14% within range.

Both boil of volume and boil effectiveness are both important.
Boil of volume = calculate target volume
Boil of Effectiveness = calculate if you are boiling hard enough / too hard.

QldKev

 

[SG9090]

Thanks guys,

i understand what your saying. I made the error of assuming the boil off is a persentage, did not realise it is litres per hour i should use.

I only boiled for an hour with 40g@60min, 30g@5min and 40@0min all Amarillo. I boiled down 55l to 49L with OG now @1.042. Will this still be ok or maybe not quite Bitter enough.


Cheers,

Shane

 

[QldKev]

Thanks guys,

i understand what your saying. I made the error of assuming the boil off is a persentage, did not realise it is litres per hour i should use.

I only boiled for an hour with 40g@60min, 30g@5min and 40@0min all Amarillo. I boiled down 55l to 49L with OG now @1.042. Will this still be ok or maybe not quite Bitter enough.


Cheers,

Shane

What was your target gravity? If you had a higher brew house efficiency than expected all may be ok. If you have lower then you should look at adding some Dried Malt Extract to get back to your planned OG. If you also adjust the sugars back up to the desired gravity, you should also add in some extra hops for the extra volume. Remember an important rule about beer is about the malt (sweetness) to hop (bitterness) ratio.

QldKev

 

[SG9090]

I had brew house eff set at 70% i did achieve 74% been 8.5kg of grain with a preboil gravity of 1.036 with 55L.

Target OG was 1.047 i now have OG of 1.042

 

[Thirsty Boy]

When you see boil oFf expressed as a percentage, there is a reason for that.

% boil off is an indicator that your boil is vigorous enough to be doing all the things like protein coagulation and evaporating volatiles that it is supposed to do. Percentages are however a lousy way to try and work out your likely pre and post boil volumes.

The amount you boil off per hour, will stay relatively static... If you have the same pot and you do not adjust the amount of heat you apply to the pot. However, depending on your actual boil off rate and the boil vigor you get, you might actually want to adjust the amount of heat.

You should be boiling off somewhere between 15 & 8 % of the starting volume of your kettle in an hour. This indicates that you are doing everything that needs to be done in the boil, but you aren't sticking in too much heat... Which can also be less than optimal for your beer quality.

So - if for instance you were getting 12% boil off in A single batch... Then decided to do a double batch and make no changes to your heat. Firstly, I think its obvious that more liquid, but no more heat, will mean a more "gentle" boil, this will reduce the actual amount boiled off per hour by an amount, and you start with more liquid, so the % boil off is halved. All in all what was a 12% boil off in a single batch, will become less than a 6% boil off in a double batch - and that's not really enough. Plus you have a more gentle boil, maybe too gentle.. You simply aren't shoving in enough units of energy into every liter to do the job of "wort boiling" properly.

So you turn up the heat... And despite what people so frequently say, if you turn up the heat, you do increase both the vigor of the boil and the amount of liquid boiled off per hour.

You need two things from a boil... {a} that it's is visibly rolling, churning & bubbling {b} that it boils off at least 8% of the starting volume per hour. And it's probably best practice to apply as little heat as possible to the system in order to get that result. Just because 8% an hour is a "minimum" doesn't mean you should just target 25% per hour on the more is better theory. More is not necessarily better. 8-15% is the "safe zone" where you know for sure you have are doing enough, but not too much.

Once you know that your boil looks good and that your percentage boil off is in the safe zone. Then - your life will be a hell of a lot easier if you just think about you boil off as a liters per hour figure. Before that, to just say "your boil off will stay the same no matter what your boil size" or sentiments to that effect - is overly simplistic, not quite accurate, and IMO, not very good advice.

Nicely - while your standard 20% per hour is a bit high (don't fritz out too much, it's not ideal but it's not a tragedy either, high is way better than low) it does mean that at 11% for a double batch, that you are smack in the middle of the target range. All you have to do is tweak your expected volumes and you're cooking (probably literally) with gas.

TB