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Old 09-19-2006, 10:13 PM   #21
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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...

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Old 09-19-2006, 10:21 PM   #22
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Hmm, looks like Sugar actually Boils Later than water...

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

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Old 09-19-2006, 11:08 PM   #23
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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?

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Old 09-19-2006, 11:10 PM   #24
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Oh, uh yes... Unless it doesn't.



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

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Old 09-20-2006, 07:03 PM   #25
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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

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Old 09-20-2006, 07:14 PM   #26
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Quote:
Originally Posted by MattD
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.
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Old 09-20-2006, 08:27 PM   #27
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Sounds like a Boil is a Boil then.

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Old 09-20-2006, 08:33 PM   #28
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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.

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Old 09-20-2006, 09:05 PM   #29
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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.

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Old 09-20-2006, 09:08 PM   #30
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Quote:
Originally Posted by Chairman Cheyco
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.
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