Full boil physics

[faber]

Some questions for the amateur (or professional) physicists or chemists out there, a category that includes any experienced homebrewer.

1. Boil-off: Is this affected by outside (ambient) temperature and/or altitude?

2. Wort-cooling: As outside temperature decreases, does the wort-cooling time also decrease? (I seem to remember in physics class that boiling water doesn't freeze faster than 10°C water if placed in the same sub-freezing atmospheric conditions, despite what common sense would have one believe. Not sure if/how the same principle applies here.) (NB: I don't have a wort-chiller, but I have a lot of deep snow in the yard.)

3. Boiling temperature: Water boils at 201°F where I live. If a recipe calls for a 60, or 90, minute boil, does that mean simply boiling, or does that mean boiling at sea-level temperature? What accommodation, if any, do I need to apply to boiling time?

Info: I live at about 5100'. We have some arctic cold coming in for a few days, and I was hoping to get out after dinner some time soon and take advantage of the sub-zero temps for the (possibly?) quicker wort-cooling. I'd like to get a really good cold break. In the spring I will get a wort chiller, but for now I don't want to mess with hoses in these temps.

It's fun to put on a Carhartt "wind bag" and sit there and drink/brew beer. It's like ice fishing, but it smells better.

TIA

 

[Bobby_M]

Wow, lots of questions but interesting anyway.

First, outside temp may delay your time to boil by a little bit especially if it's windy. The pot will continually be cooled by passing cold air. It would probably help to build a little wind sheild around 3 sides if you always have wind.

I would think that hop acids would be extracted faster at sea level boiling temps 212F but you can just compensate a bit by boiling a bit longer (5 minutes) but really, the temp difference is not that large.

Cooling wort from the exterior of the pot is always going to take longer due to the surface area exposed to the wort. Let's say you have a 12" diameter pot and you're able to continually pack snow to the height of 12". That's 450 square inches of surface area.

Take a 50' chiller with 3/8"OD tubing and you're exposing 700 square inches to the wort.

The other difference is in how quickly the warmed water is flushed away allowing new cold water to grab heat. In a snow pack, that water will drip down the pot and leave a gap between the pot and snow (no heat transfer). You might be better off using a big rubbermaid tub filled with water that has been sitting out to near freezing. As it warms, keep dropping packed snow/ice in. (how about an inflatable kiddie pool?)

Finally, the speed of cooling will be greatly increased if you stir your wort continuously so that the hot/cold zones are continually mixed.

 

[david_42]

http://ift.confex.com/ift/2004/techprogram/paper_25787.htm

"rate coefficient of 0.0153(1/sec) for atmospheric boiling conditions"

The lower temperature will require longer boil times.

 

[zoebisch01]

It's fun to put on a Carhartt "wind bag" and sit there and drink/brew beer. It's like ice fishing, but it smells better.

Lol, that's funny

Yes, boiling is boiling. It is more or less a physical phenomena and the corrections david posted are basically account for the difference in atmospheric pressure. So the higher up, the less pressure that must be overcome for the liquid to change into a gaseous phase (which is really what happens). Now you can get degrees of boiling based on the factors you mention and the heat output of your burner. A strong rolling boil is what you want, not a gentle boil (you will see the difference and recognize it when it happens).

 

[TheJadedDog]

http://ift.confex.com/ift/2004/techprogram/paper_25787.htm

"rate coefficient of 0.0153(1/sec) for atmospheric boiling conditions"

The lower temperature will require longer boil times.

Seriously, is there anything you don't know?

 

[Kaiser]

1. Boil-off: Is this affected by outside (ambient) temperature and/or altitude?

I will be affected by altitude since it amout of energy needed to evapoate water is less at a lower ambient pressure. Just ajust your burner to stay between 10 and 15%/hr boil-off rate

2. Wort-cooling: As outside temperature decreases, does the wort-cooling time also decrease? (I seem to remember in physics class that boiling water doesn't freeze faster than 10°C water if placed in the same sub-freezing atmospheric conditions, despite what common sense would have one believe. Not sure if/how the same principle applies here.) (NB: I don't have a wort-chiller, but I have a lot of deep snow in the yard.)

You could make an ice water bath in a big tub and cool the worth with that. Kep the wort moving a little to speed up the chilling. But there should be some natural convection in the bot as the coling wort will "fall' down the sides of the pot thus exposing warmer wort to the cooling surface.

3. Boiling temperature: Water boils at 201°F where I live. If a recipe calls for a 60, or 90, minute boil, does that mean simply boiling, or does that mean boiling at sea-level temperature? What accommodation, if any, do I need to apply to boiling time?

This boil temp is only one of the many factors that we don't account for when estimating IBUs. Just adjust your recipe based on the hop utilization experiences that you had with previous batches.



Kai

 

[faber]

http://ift.confex.com/ift/2004/techprogram/paper_25787.htm

"rate coefficient of 0.0153(1/sec) for atmospheric boiling conditions"

The lower temperature will require longer boil times.

According to that linked paper, the longer boiling time essentially accommodates proper hop isomerization, which is one of the reasons for such long boils in brewing, I'm assuming. Correct?

Could you kindly give me an example of how to adjust my boiling time with that coefficient?

 

[faber]

Wow! Thanks to all for your replies. So many good suggestions.

When I do this, I go out to a part of my property that is fairly well sheltered by trees and terrain. There is no shortage of snow either. But I think I'll bring a big ol' garbage can that I cut down a little for icing a keg and just fill it with snow. I'm guessing the heat of the pot will make enough icewater out of it.

I've only recently moved up to full boils and have had some success with cooling the wort in the snow. I start a modest whirlpool action and pack the pot (32qt) in the snow, repacking every ten minutes or so.

I was just wondering if there will be a significant advantage in going out tomorrow night to brew when it should be down to -14°F, and then I started to wonder about all these related altitude/temperature issues.

In previous brews, I tend to enjoy the recipes that call for 90 minute boils, as opposed to 60 minutes. I guess now I know why.

A follow-up question:

Is there any harm in simply adjusting 60-minute recipes to 90-minute versions (by just increasing the hopping intervals by 50%)? (Is this what you're getting at, Kaiser?)

 

[Bobby_M]

Wow! Thanks to all for your replies. So many good suggestions.

I'm guessing the heat of the pot will make enough icewater out of it.


I was just wondering if there will be a significant advantage in going out tomorrow night to brew when it should be down to -14°F, and then I started to wonder about all these related altitude/temperature issues.

In previous brews, I tend to enjoy the recipes that call for 90 minute boils, as opposed to 60 minutes. I guess now I know why.

Just remember to keep throwing new packed snow in because that icewater will continue heating up as the wort is cooling. You want to keep that water as cold as possible while whirpooling your wort.

Brewing on a particularly cold night will only serve to freeze your ass off while the wort will be relatively unaffected because air to liquid and vice versa is so inefficient.