Define "BOIL"

[marshman]

So, as I'm makin' my beer last night I got to wonderin' about something. I bring some water to boil, pull from heat to add LME (learned the hard way) and return to heat once it's all pretty much dissolved. I had turned the burner down to @ 75% while I was off of it, forgot to turn it back to full. Set timer for 10 minutes for 1st hop addition. 10 minutes comes and goes, add hops, NOW I set back to high, reset for 35 min for next hop addition. 8 minutes into this phase, or 18 minutes since I put it back on the heat, I get back to a full boil. I finish the regularly scheduled timing as if it'd been boiling the entire 60 minutes, but wondered if I need to wait for a proper "Boil" to start the clock. It was definitely hot & steamy the whole 60 minutes, just not at a full, rolling boil. Is it essential to boil, or just be real, real hot?

 

[Bobby_M]

That's a good question that I wondered myself. I noticed that even when the wort is kinda churning/rolling steamy, the temp is actually about 205dF, not 212. It takes quite a bit of time to get to 212 with my 3 gallons of wort, even on a 12kBTU burner.

 

[Brewno]

I've assumed a full rolling boil but never considered temperature.

These are two interesting questions and I'm now very curious. I'll have to browse "How To Brew" and Papazian.
Oh and let me not forget David 42, member of these forums whom I find very knowledgeable (one of among the many here).
I'm becoming a fan, Dave

Tommy

 

[Chairman Cheyco]

Well, has been a bit of debate about this. I was under the impression that you needed a really vigorous boil to get the hops banging around in there to get the acids isomerized, and also to get the hot-break to coagulate. While this is true, I have recently discovered that too-violent a boil will result in increased melanoidans and caramelize your wort, even with a full-wort boil.
The answer to your question lies in boil-off rates. This is expressed in percent of wort volume lost to evaporation per hour. Below 8% is not enough to drive off dimethylsulphide (DMS) which will give your beer a sweet-corn-like taste, 9%-15% is the sweet spot and anything above 15% will encourage melanoidans and caramelization of the wort.

 

[the_bird]

The impression that I've gotten is that a full, rolling boil is necessary for hops utilization and to get a good hot break (like Cheyco says - listen to any man named "Cheyco"). It's not just getting the wort hot. It has been very difficult for me on the stove; I think there may be a scientific reason why it's so much more difficult to get those last couple of degrees of temp before the boil (it always wants to stay at around 208 - 210 unless I have the lid partially on). I've invested in a turkey fryer in large part so I can get the full boil.

 

[Chairman Cheyco]

Don't forget about altitude. I live up high, and my wort never sees 212F, I think mine boils around 209, or maybe even a bit less. And watch out with that lid Bird, you're heading for boil-over city )), not to mention possible DMS problems.

 

[the_bird]

Well, that's why I've got the fryer (don't you read? )

It was always a compromise; full boil or no lid, had to pick.

 

[Chairman Cheyco]

Sometimes I read, when it suits me...

 

[boo boo]

I was told that when removing the heat from a boiling pot to make additions, you stop the clock as it were, and then start it back up when it comes back to a boil.
Reasoning is that for bittering purposes you need a full boil to acheive isomerization of the hops and that you generally need 60 minutes to 90 minutes of this for bittering.

 

[Brewno]

I was told that when removing the heat from a boiling pot to make additions, you stop the clock as it were, and then start it back up when it comes back to a boil.

Now that's a surprise. I didn't know you had to remove the heat before adding hops. I just put my hops (in bags) right in the boiling wort.
The more I read the more I have questions

Tommy

 

[boo boo]

Now that's a surprise. I didn't know you had to remove the heat before adding hops. I just put my hops (in bags) right in the boiling wort.
The more I read the more I have questions

Tommy

What I should have said was for adding extract or anything else that could stick to the bottom of the kettle and burn/scorch.

Sorry

I don't stop the boil to add hops.

 

[Brewno]

Well that's good news

Tommy

 

[Pirate Ale]

So the answer is?...

I would like to know how to calculate boil off rate. I think the problem with my slightly sweet first brew may have been that an electric stove will not get my kettle to a full rolling boil. It just getts to a mild churn.

>>Goes to look for jet engine to properly boil wort...:rockin:

 

[Chairman Cheyco]

Boil off rate is simply your (preboil volume - postboil volume)/preboil volume*100

 

[AdIn]

Boil off rate is simply your (preboil volume - postboil volume)/preboil volume*100

Then devide it to hours boiled if you want boil off rate for one hour.

 

[Pirate Ale]

Ok, walk me through this. Extract partial boil.
Used 2 gal. water and 6.6 lbs LME, .6 lbs DME
Boiled 1 hour, added to primary with 3.25 gal. cold water, to = 5 gal.

What would the calcualtion be, as far as including the volume of the malt extract?

Without adding the volume for the malt, it would be 2 - 1.75/2*100 =12.5%

 

[Chairman Cheyco]

Yup, you got it.

 

[Reverend JC]

"A boil is a boil no matter if it is a slow boil or a full rolling one." This is what my sister-inlaw(a food science major) said as my brother and I debated the same thing while boiling the wort. I can tell you that our minimal boil we used did not create the hot break.

 

[pbowler]

Boil is a Chemical state as it were, not a temperature.

WATER boils at 212F, but WATER also has a OG of 1.000.

WORT is not WATER, I'm not implying that gravity and boiling have anything to do with each other, although they may, I'm just stating that different compounds have different Boiling Points (Defined as the Temperature at which a Liquid turns to a Gas).

It is likely (as some of us have noted) that wort has a Lower Boiling Point (Temperature) than Water, Probably due to the Sugars in the Wort, which actually may mean that Gravity and Boiling point and Inversly related.

Whats the Boiling point and Gravity of Corn Sytup? Likely High Gravity, Low boiling Point?

 

[Chairman Cheyco]

Well if you're going to get that technical, you need to figure out if you're actually boiling the sugar or boiling the water out of the sugar solution. The vapor coming off wort is pure water. Once you boil all the water out of your wort, you'll have liquid sugar and it's boiling temperature will be much higher. The aqueous sugar solution may have a different boiling point, but it's still only water coming out.

 

[pbowler]

True, but it isn't just water. Water with salt in it boils faster [EDIT: slower actually, Salt raises the boiling point of water] than water without salt.

Salt and Sugar both dissolve in water, therefore it cannot be treated as water for the purpose of figuring a Boiling point.

my head hurts...

 

[pbowler]

Hmm, looks like Sugar actually Boils Later than water...

oh well, that's whi I have a degree in Economics...

 

[Pirate Ale]

So all that really doens't answer the question. Is a slow boil on an electric range going to give the hot break needed, as compared to a high rolling boil?

 

[Chairman Cheyco]

Oh, uh yes... Unless it doesn't.



It should, but the only way to sure is to try it.

 

[MattD]

Here's the chemistry answer. Any contamination of a substance will expand the temperature range for which that mixture is solid. This is commonly used in labs to determine contamination of solids, a powder is slowly heated, and the temp at which it melts is recorded. That temp is compared to the melting point of the pure substance, and the difference shows how much contamination is present. Remember the scene from Blow when peewee is testing the coke's purity? Same thing is at work here, except contamination raises the boiling point. So, if water boils at 100C, after you contaminate it with sugar that BP will climb higher. So the wort should boil at a higher temp than pure water. Now, once it's boiling, that's it, it's boiling. There should be no difference in water temperature between a slow boil and a rapid boil, because the water is busy changing states and all the heat energy being added is going toward vaporizing the water, not heating it. The reason the boil might be slow at 75% burner and rapid at 100% burner is because you've increased the rate of heat input. Those bubbles are pockets of vaporized water nucleating on the surface of the pot. The faster you input heat energy, the faster water is vaporized and thus more bubbles form. The temperature of the water stays the same though. In fact, it's possible to supply heat so quickly that you would form a complete vapor barrier between the water and the pot, at which point you'd see the bottom of the pot begin to overheat and glow red. This is a one of the things nuclear boiler operators concern themselves about. Anyway, point is, the temp of the water is the same no matter what the boil rate is, and that temp is higher than 100C if there's sugar dissolved. Chemical reactions in the wort shouldn't be affected by the speed of the boil, theoretically, but the mixing action of a fast boil may contribute something to it, preventing a gradient from forming or some jazz like that.

As far as why an electric stove has trouble getting those last few degrees of temp, it's just a matter of energy in - energy out = mass*Cp*change in temp. The energy in coming from the stove is maxed out, but the energy out increases as the temperature increases (the temperature gradient between the hot water and the surrounding air is higher, thus there is a larger driving force for the energy to go to the air). At a certain temperature the energy in - energy out will equal 0, and the temp will stop climbing, whether it's boiling or not. Ways to get the temperature to go above this bottleneck are using a lid (increases the pressure and reduces convective heat loss) or swapping from a metal to a ceramic pot (reduces the conductive heat loss). Or you could just do your boil in a room with an ambient temperature of 80C

 

[Chairman Cheyco]

Chemical reactions in the wort shouldn't be affected by the speed of the boil

This is true (as with the rest of your very well written post I might add,) and as you alluded to, mechanical reactions contribute a big part of what goes on during the boiling of the wort. Clumps of protien bang around and stick together, as well, the isomerization of the hop oils also needs mechanical assistance.

 

[pbowler]

Sounds like a Boil is a Boil then.

 

[dougjones31]

Stick a thermometer in a slow gentle boil....you know, the kind where you have to look close to see the slight mound that the rolling water is forming.

Now turn up the heat and watch the thermometer. The extra energy leaves the pot as steam and the temp remains constant. The hotter the flame the faster the boil but the temp remains constant because the extra energy from the flame is leaving in the water vapor.

They both have the same temp
.

The Hot Break is based on temperature, so the two types of boils will do the same hot break. Time is more of a concern when you want a good hot break. You have to leave the malt exposed to the heat until the hot break happens.

 

[AdIn]

Last weekend I used my new 8 gallons boiling pot for a first time. Unfortunately I don't have a turkey fryer yet but I managed to bring approximately 7 gallons of wort to boil on my electric stove using 2 burners at the same time. It was not as vigorous boil as I had with 3 gallon pot, but, boil is a boil. That's what I thought. I boiled it for a little over 1 hour and my boil off rate was close to 15%. But after I cooled my wort it was kind of milky :-( I pitched yeast any way and put it in to fridge to ferment @48F. Day later wort cleared and I noticed unusual cottage cheese like sediment on the bottom of my carboy. The only explanation I have so far for this is that intensity of boil was not enough to link all those proteins in to something which can be easily precipitated with cold brake. To me it confirms Chairman's mechanical reaction theory.

 

[MattD]

This is true (as with the rest of your very well written post I might add,) and as you alluded to, mechanical reactions contribute a big part of what goes on during the boiling of the wort. Clumps of protien bang around and stick together, as well, the isomerization of the hop oils also needs mechanical assistance.

What kind of isomerizations are we talking about here? I can understand needing mechanical assistance to emulsify the oils in the water, for instance, but isomerization is a chemical reaction. I'm not knowledgeable of the mechanism of these reactions, but isomerization is usually intramolecular, although I can certainly acknowledge the possibility that these molecules are helping each other isomerize, in which case agitation may help bring them together at a higher rate.