Tough theory on rolling boil

[bikefoolery]

... divided into 3 classifications: smiling, rolling & hard/vigorous.

Wow, I thought those were reserved for relationships.

-the fool

[Ozwald]

If those are the only 2 options that's real easy. It doesn't matter how big of an element you put on those circuits. The 10A circuit will max out at 2300 watts & the 16A at 3680 watts.

But the question I am trying to answer is really - what size (and possibly shape) of brew kettle could you get if you are limited to N watts? Trial and error is not a good process for planning a brewery. I realize that the question I am asking is a difficult one (googling it really yields nothing), but I do think there is a good answer to it. I cannot do experiments since I have no way of limiting the power (dimmers for the kW range are not cheap), otherwise I would have (volume, shape and gravity as variables).

I am not really looking for the answer for my own brewing at the moment (I have done my upgrades), but it would have been nice to give other new brewers some help. Also... I kind of enjoy solving problems...

Then I revert to my first answer:

Good luck.

Personally I don't think electric is the way to go for beginners. If they've brewed with someone else a few times & realize all the work that's involved (& have a good idea that it's something they want to persue) then by all means go for it. But I wouldn't try to cheap out on anything: get the appropriate power source, get the PID, get the appropriate elements, learn Ohm's law & how to wire everything correctly/safely. Trial and error is not a good process for learning about electricity either. Not saying any of that is difficult, but it's not exactly cheap, especially to brew a few times & realize that they don't really care for it.

[yeastculture]

Personally I don't think electric is the way to go for beginners.

That depends on what is available to the brewer, does it not? While I think almost everyone will start out stovetop it may be very limited if you have an electric stove (99% in Sweden do). The normal way for beginners to get a proper batch size here is to use some kind of heat stick while boiling on a stove. Propane is not really an option for most people here - brewing outdoors in 0-10 degrees F, in darkness and knee-deep in snow, is generally considered hard-core. It bothers me when my brewday beer freezes while I am drinking it...

Going electric does not automatically mean having a PID controller or wiring anything on your own - it simply means that you heat with electricity and it does not have to be very expensive (but buying the wrong stuff is still no fun).

[Stinkfist]

Personally I don't think electric is the way to go for beginners.

That depends on what is available to the brewer, does it not? While I think almost everyone will start out stovetop it may be very limited if you have an electric stove (99% in Sweden do). The normal way for beginners to get a proper batch size here is to use some kind of heat stick while boiling on a stove. Propane is not really an option for most people here - brewing outdoors in 0-10 degrees F, in darkness and knee-deep in snow, is generally considered hard-core. It bothers me when my brewday beer freezes while I am drinking it...

Going electric does not automatically mean having a PID controller or wiring anything on your own - it simply means that you heat with electricity and it does not have to be very expensive (but buying the wrong stuff is still no fun).

Just becareful with those heat sticks....they are easy to make and easy to kill yourself with...make sure you use the proper safety equipment that goes with them...

[yeastculture]

Just becareful with those heat sticks....they are easy to make and easy to kill yourself with...make sure you use the proper safety equipment that goes with them...

I have never used one of the heat sticks - just telling you how new brewers usually do it "over here". I do not really think that a factory manufactured heat stick is more dangerous than a propane burner, but I think anything you use to boil six gallons of wort is something that could kill you, and something you should be careful with.

All this talk about the electrical stuff is off-topic though (I am an engineer with a fair understanding of electricity) - the question is about the power required to keep wort at a rolling boil, regardless of heat source (burners give you watts as well, even if you normally mention BTUs). As I mentioned before - I have some of the pieces of the puzzle - but I cannot find how to calculate what evaporation rate you actually need for something to become a rolling boil. Ozwald mentioned he likes 13% evaporation rate, and I have read that it is usually 10-15%. I could base my calculations on a 15% evaporation rate and be done with it, but I would rather be more precise than that if it is possible. My gut feeling is that you can calculate (approximate well enough) the power required to give you a good exchange of wort from the bottom to the top of the kettle ("a proper rolling boil").

[Bugeater]

As I mentioned before - I have some of the pieces of the puzzle - but I cannot find how to calculate what evaporation rate you actually need for something to become a rolling boil. Ozwald mentioned he likes 13% evaporation rate, and I have read that it is usually 10-15%. I could base my calculations on a 15% evaporation rate and be done with it, but I would rather be more precise than that if it is possible. My gut feeling is that you can calculate (approximate well enough) the power required to give you a good exchange of wort from the bottom to the top of the kettle ("a proper rolling boil").

What I see here are attempts to do complex calculations that are totally unnecessary for the homebrewer. Just by eye, you can adjust your boil so that you maintain a boil that is rolling but not violent. With just a few brew sessions you can get that same level of boil every time. The biggest factor in evaporation rate is kettle geometry once you can get a consistent boil intensity. Each kettle will have a characteristic boil off rate for most brews. This will change slightly do to wort gravity and/or ambient temperature.

Trying to compute boil off rate as a percentage is extremely difficult because it will vary widely due to changes in volume of the starting wort. For a given kettle at the above mentioned boil intensity, you will always boil off the same volume of wort in a given amount of time. If your volume is off by a quart or two either way (very common in homebrewing) the % boil off will be different but the volume boiled off will remain the same. For example, beginning with 5 gallons of wort, a typical boil off rate is 1 gal/hr, that is a 20% boil off rate. If you started with 5.5 gallons that rate would change to 18% assuming everything else is the same.

One of my kettles boils off 1 gal/hr, the others go off at 1.2 and 1.5 gal/hr. I base my starting volume on which kettle I plan to use and always finish up within a pint or so of my planned post boil volume at the desired gravity. No fancy calculations, just adding my known boil off volume to my desired preboil volume tells me exactly how much wort I need from the mash tun. Keeping it simple gives me consistent results with minimal calculations.

[IAmRight]

I could base my calculations on a 15% evaporation rate and be done with it, but I would rather be more precise than that if it is possible. My gut feeling is that you can calculate (approximate well enough) the power required to give you a good exchange of wort from the bottom to the top of the kettle ("a proper rolling boil").

You, and most of the posts, are very far down a dead end trail. You need to backtrack.
You will never be able to calculate the exact element size needed, even after brewing on the same system a billion times. Real life brewing is very different from a theoretical word problem in an engineering textbook. There are too many factors that vary from brewday to brewday- gravity, volume, wind, ambient temp, pressure, etc.

Stepping back even further, you need to GET to a boil, before you can MAINTAIN a boil. That first requires much more heat input than the second.

There is absolutely no feasible way (translation: it is impossible) to use electric elements to maintain (and control), a boil without over-sizing the element, and using some sort of adjustable power control. The best solution is the common (and cheap-$40USD) PID (only really used as a manual variable power device). I don't brew electric, but have seen videos and write ups, and <5% power variations can be the difference between losing the boil, and losing your beer due to boil-over.

The total amount of watts you need to reach a boil in an acceptable time frame will vary, as will the amount to maintain a boil. This may exceed a single circuits maximum rating. In that case, you can use multiple elements powered by multiple circuits, with only one PID controlling the (oversized!) element used to maintain the boil in order to save money. There is no need to resort to 3 phase (it is not needed for PIDs). Although, I thought you guys had 3 phase readily available at the residential level. Most electric brewers in North America run a new dedicated high amperage circuit just for brewing, because there usually isn't enough power available in any one location (and the wives usually frown on cords strung about).

Go back and re-read the post where the sizing and watt density choice was explained- the highest watt rating possible for the circuit, but not if watt density has to be increased.

I know you Swedes are a inventive bunch, and the rest of the world thinks we Yanks are a bit slow witted, but when solving a problem results in beer going in our pie holes, we somehow manage to step up our game. There is more than enough information about electric brewing and general wattage recommendations for every size system on the many brewing forums. Although, I think the most widely followed is Kal and the electricbrewery, and he is Canadian, which may mean we are really only smart enough to let our neighbors figure it out, then steal it.