Vigorous Boil Reduces To Gentle Boil

[Steve]

Ive noticed with the last couple of my brews that I start out with a very excited vigorous boil at the beginning of the 60 mins and it slowly reduces over the 60 mins to a nice calming gentle boil verging on hardly any bubbling at all? I mean its still boiling but not with so much vigour as at the beginning. Anyone else have this. Is it a problem? Any scientific explanation? I use a 3 ring burner with adjustable reg and 50 litre steel vessel as a kettle.
Cheers
Steve

 

[domonsura]

Does it happen when you have the burner on full noise, and do you notice the sides of the bottle getting really cold when it happens?
Maybe it's the flow capabilities of the gas bottle not being able to keep up as the boil progresses?
With higher gas flow rates, sometimes bottles have a little trouble keeping up, in some cases you get icing/freezing occurring on the outside of the bottle. Are you using a 9kg bottle, or a smaller one?
Try sitting the bottle in a bucket of water so it has a 'heat sink' to absorb some of the chill the bottle is trying to lose to keep up the gas flow.
I particularly noticed this when I was using my gas forge with a 9kg, the bottle would ice up and the flow would drop down to the point the burner would actually go out. I got a 45kg bottle instead, and never had a problem again.
Not sure if this is what's happening for you, but possibly. There's an equation that works out whether a bottle should be able to keep up with flow demands from burners, but i can't remember it. Maybe there's a gassy here that can explain it. Something to do with the diameter of the bottle, which relates to the available liquid surface area inside the bottle that allows the LPG to turn from liquid back into gas at the required rate. I think . The process of going from liquid to gas is an endo-thermic one ('absorbs' or dissipates heat) just like any evaporation process :blink: I'm sure someone else can explain it better.

 

[Steve]

Does it happen when you have the burner on full noise, and do you notice the sides of the bottle getting really cold when it happens?
Maybe it's the flow capabilities of the gas bottle not being able to keep up as the boil progresses?
With higher gas flow rates, sometimes bottles have a little trouble keeping up, in some cases you get icing/freezing occurring on the outside of the bottle. Are you using a 9kg bottle, or a smaller one?
Try sitting the bottle in a bucket of water so it has a 'heat sink' to absorb some of the chill the bottle is trying to lose to keep up the gas flow.
I particularly noticed this when I was using my gas forge with a 9kg, the bottle would ice up and the flow would drop down to the point the burner would actually go out. I got a 45kg bottle instead, and never had a problem again.
Not sure if this is what's happening for you, but possibly. There's an equation that works out whether a bottle should be able to keep up with flow demands from burners, but i can't remember it. Maybe there's a gassy here that can explain it. Something to do with the diameter of the bottle I think, that allows the LPG to tun from liquid back into gas at the required rate.

Yep DM - I have all the 3 small brass handles on the burner fully open. When I first got it I remember I had to turn 1 of them off because the boil was going vigorous for the full 60 mins. Its a 9kg gas bottle. I havent noticed it icing up though. Its like you say its as if it cant keep up with the demand that is actually coming out of the burners. Will have a fiddle tomorrow. The only thing I can think of is if its a windy day (I brew under the carport, which is often like a wind tunnel) I put a few wind wooden wind breaks around the kettle on the floor. But this wouldnt equate to a gradual reduction in vigour? Its an odd one. Thanks.
Cheers
Steve

 

[Zizzle]

I have an electric boiler, so take this with a grain of salt, but isn't there issues with the paint on new burners melting and blocking up the holes?

 

[Steve]

I have an electric boiler, so take this with a grain of salt, but isn't there issues with the paint on new burners melting and blocking up the holes?

cheers Zizzle it was secondhand so no paint.
Steve

 

[Shunty]

I get a similar sort of thing when the bottle is getting a bit empty, the whole bottle ices up and the flow drops off. Try giving the bottle a shake, seems to wake up my burner alright. otherwise the tub of water helps

 

[Steve]

I get a similar sort of thing when the bottle is getting a bit empty, the whole bottle ices up and the flow drops off. Try giving the bottle a shake, seems to wake up my burner alright. otherwise the tub of water helps

Cheers shunty its a full bottle. Will give it a shake and try it in a bucket.
Steve

 

[Doogiechap]

G'day Steve,
I reckon there are 2 factors. Definately the gas bottlle supply and demand issue (has happened to me too). But Ihave also found that as the SG increases from evaporation that more heat is required to achieve the same vigor.
Then you go and throw some hops in and fizzzzzz as the wort boils over and makes a big caramel mess .
Cheers
Doug

 

[domonsura]

I was wondering about the increase of SG having an effect myself. Guess that also makes sense.

 

[Steve]

Doogie and DM.... not sure I follow you? So the more hops you add the less vigorous the boil becomes. The last couple of brews have actually had 4-5 additions rather than say 3. When you say SG - do you mean Starting Gravity?
Cheers
Steve

 

[DJR]

SG=specific gravity, can't see how the 10% increase would do much for it

My money's on the burner heating up or a supply/demand issue. Is the flame height the same, take a photo at starting and finishing so you can compare how the flame is going - does it turn very orange after starting blue?

 

[Steve]

SG=specific gravity, can't see how the 10% increase would do much for it

My money's on the burner heating up or a supply/demand issue. Is the flame height the same, take a photo at starting and finishing so you can compare how the flame is going - does it turn very orange after starting blue?

nope - blue all the way through at the same height...ive had my eye on it DJR

Cheers
Steve

 

[DJR]

Why don't you boil a few L of water on it - does the vigor of the boil change through the hour? Interested to know if it's a wort thing or happens with just water.

 

[Steve]

I just took the black screw cap off the reg (which ive never done before) and found the adjustable bit that has the + and - sign. It was screwed right round to the - sign. That must be it? Will have a play tomorrow and crank it round to the + sign.
Cheers chaps
Steve

Yes DJR it reduces in vigour through the 60 mins.

P.S. It does take 40 mins to get 25 litres to the boil

 

[domonsura]

I just took the black screw cap off the reg (which ive never done before) and found the adjustable bit that has the + and - sign. It was screwed right round to the - sign. That must be it? Will have a play tomorrow and crank it round to the + sign.

ahhhhhhhhh...careful there big guy......aren't they usually factory set? :blink: best of luck....(innards of regs=trouble to me...quite happy to play with the gas coming out of the reg, but never with the reg....)

 

[Doogiechap]

Doogie and DM.... not sure I follow you? So the more hops you add the less vigorous the boil becomes. The last couple of brews have actually had 4-5 additions rather than say 3. When you say SG - do you mean Starting Gravity?
Cheers
Steve

Sorry Steve the hops comment was a throwaway line that hop additions always keep me on my toes for boil overs immediately after the addition (at leadt for me).

SG=specific gravity, can't see how the 10% increase would do much for it

My money's on the burner heating up or a supply/demand issue. Is the flame height the same, take a photo at starting and finishing so you can compare how the flame is going - does it turn very orange after starting blue?

DJR yes it's only a 10% variation but how much do you tweak your reg/ burner to get a gentle to vigorous boil (not much for me).

ahhhhhhhhh...careful there big guy......aren't they usually factory set? :blink: best of luck....(innards of regs=trouble to me...quite happy to play with the gas coming out of the reg, but never with the reg....)

Domonsura I think they are factory set but I pulled one of mine apart to inspect the integrity of the internal rubber diaphragm and found that the adjustment screw just increases/ decreases pressure on the diaphragm via a soft spring and unless you tweak the hell out of it I don't think there will be any issues.
Cheers
Doug

 

[Steve]

phewwww - i just fiddled (turned) a little bit and then turned it back :blink:

 

[randyrob]

werks alot better without the spring in :beerbang: HTFU guys

 

[blackbock]

This is an interesting phenomenon. I am wondering whether it has happened on several occasions, or just once?
Personally I have never had to turn my NASA up anywhere near its maximum - to be honest I find that a frightening idea, I can't get near enough to the kettle to be able to watch for boilovers, and maybe this occurence just has something to do with the initial heating up of the liquid. Later when the temperature is more even perhaps there is not such a tendency to bubble so much?

 

[domonsura]

Yeah, I don't turn my NASA up full blast either. Too much....