Measuring Kettle Boil-Off Rate - Several Questions Please

[Jiffster]

These may be a stupid questions but here goes anyway.....

1) My brew kettle has a sight glass with a mark at each gallon. Can I use this to determine my boil off rate or do I need to use something else?

2) When calculating boil off rate, I put 5 gallons of water in, bring to a boil and start the timer for 1 hour. After 1 hour I shut her down and then wait for water to cool to what temp before measuring amount losses to boil?

3) Do I put lid on while water is cooling so I don't lose extra to evaporation?

 

[jwalk4]

1) Yes, you can use the sight glass if it is accurate. Double check by filling a carboy, or bucket up with a known and reliable measurement.

2) I would put more than 5 gallons in because (I assume) you'll be filling your kettle with more than 5 gallons when you are hoping for 5 gallons of packaged beer. Try 6.5 gallons and see if you wind up with 5-5.5 gallons at the end of your hour.

3) After completing your hour long water boil, I would chill the water as you plan to do on your actual brewday (ie lid off, plate chiller/immersion chiller/ice bath, etc.). You'll have a better idea of your wort volumes on your actual brewday if you do.

But that's just one man's opinion.

 

[Jiffster]

OK, my boil-off rate test didn't go well. Heating up 7 gallons and after 1.5 hours water was just starting to show signs off boiling and I was already down alonost a gallon.

I stopped the test because I figured there must be something wrong with my test process.

I think I should have put the lid on until the water started boiling, then took the lid off and started the timer.

 

[Gavin C]

I wouldn't bother with a test run. I'd do a brew with a nice comfy (to style) margin either side of planned OG and volume, take accurate readings and learn from it.

I'd use a starting default of 1 gallon boil-off/hour and adjust from there based on accurate temperature corrected volume readings on brew day. (be sure to account for hop absorption and dead spaces too)

You can learn about other things like hoses/chiller/kettle headspace without a boil.

I wouldn't be willing to invest the time and effort in a test boil.

If you do a test boil, boil for 15 mins and get your hourly rate that way. Less time effort and expenditure of NG/propane/electricity.

Yes cover the pot before getting to a boil and after the boil is complete. When brewing, you can cover the pot to reach a boil to shorten time. Once boiling timer starts, off comes the lid.

Any test can mimic that

 

[cyanmonkey]

You lost a gallon and didn't even boil?

 

[jwalk4]

What is your heat source? Stove, propane burner, or other?

Also, a test boil is also a good idea for pot passivation which protects your investment.

 

[Gavin C]

Also, a test boil is also a good idea for pot passivation which protects your investment.

Never thought of that. Smrt

 

[Jiffster]

I was using propane with an SQ14 burner. I may have achieved boil temp but I was waiting for a rolling boil. Then when I tested the temp it read 213F. That was probably due to the steam.

At that point I noticed how much water I had lost and I figured any data I gathered at that point would be to skewed to be useful.

What is "pot passivation"?

 

[MaxStout]

I'm with Gavin on determining boil-off empirically in real brews.

With a test boil you might not have the boil rate the same as you will with wort. Boil rates can vary widely, depending on amount of heat applied. When boiling wort, you will adjust the flame to just the right point for a good rolling boil while avoiding boilovers. That boiling "sweet spot" may be much different than what you'd be applying to a kettle of plain water.

Use Beersmith or an online volume calculator to estimate starting volume and go from there. If you overshoot or undershoot you can make a note to adjust the volume next brew. After a couple brews you will have the volume dialed in.

Edit: Passivation is creating a protective layer of oxide on aluminum. If you have an aluminum kettle, you should boil some water in it for 30 minutes or so to create this layer before doing your first brew. For stainless steel, passivation isn't as critical before first use.

 

[Gavin C]

I was using propane with an SQ14 burner. I may have achieved boil temp but I was waiting for a rolling boil. Then when I tested the temp it read 213F. That was probably due to the steam.

At that point I noticed how much water I had lost and I figured any data I gathered at that point would be to skewed to be useful.

What is "pot passivation"?

Ignore boiling temperature. It is what is is determined by the air pressure, humidity and makeup of the water/wort.

Once your boiling its boiling. Temperature doesn't matter a damn as it won't change regardless what you do. This is the latent heat of evaporation. Drop in a couple of rods of hot plutonium and it will still remain the same. Does not matter.

It is not possible to boil it at a higher or lower temperature unless you change the air pressure. (Camp in the Himalaya or use a pressure cooker). Pointless measuring.

It's a yes \ no bit of dat. Is it boiling yes/no?

 

[CA_Mouse]

With that particular burner it shouldn't take 1.5 hours to get to boiling unless you filled it with very cold tap water. I have the same burner and it does take a long time to heat my sparge water from cold to strike temps. Boiling after my mash takes less than 30 minutes. Try heating it with the lid on until you get close to boiling, then boil without the lid and then chill with the lid on if you have the ability.

Here is a link to Passivation

 

[back2u]

Gavin is correct. Water boils at a given temperature which varies slightly based on atmospheric pressure. Water boils at 212F at sea level and at about 202F if you live in Denver. Once you reach a boil, increasing the burner heat makes the boil more vigorous, but increases the temperature of the wort very little - the extra heat is simply being converted to steam, otherwise known as boil off. And guess what - you can brew beer just fine in Denver, so any temperature above 200F is going to create the chemical reactions you need from a 60 minute boil.

Minimize boil off by bringing the wort to a slow rolling boil - just enough to see some bubbling and turnover in the wort. This keeps the liquid moving and you don't have to stir it much. Anything above that is a waste of burner fuel and all it does is create a higher boil off rate. One gallon per hour is a good starting point, but you should be able to reduce that to one half to three quarters gallon per hour by backing off on your burner heat. My boil off starting with 6 1/2 gallons is just over 1/2 gallon. To save energy, leave the cover on while bringing up to boil, and then remove it for the 60 minute boil to let the bad stuff escape.

Impurities in water, i.e., higher gravity wort, increases the boil temperature slightly but not enough to be a consideration for home brewing.

 

[MagicMatt]

It is not possible to boil it at a higher or lower temperature unless you change the air pressure. (Camp in the Himalaya or use a pressure cooker). Pointless measuring.

Not true. Adding salt will cause the boiling point to rise. You can calculate this using the ebullioscopic constant.

Although I'll concede that in the realm of brewing one should never reach such large proportions of adjuncts (enough to sway the boiling point).

 

[Gavin C]

Not true. Adding salt will cause the boiling point to rise. You can calculate this using the ebullioscopic constant.

Although I'll concede that in the realm of brewing one should never reach such large proportions of adjuncts (enough to sway the boiling point).

Funnily enough, I though bringing up salt editions and the ebullioscopic constant was not warranted in my response to a thread in the beginners' section.

 

[MagicMatt]

Funnily enough, I though bringing up salt editions and the ebullioscopic constant was not warranted in my response to a thread in the beginners' section.

Fair enough point, and I see that sentiment often in this subforum, but I don't agree with it or understand it. We were all beginner brewers at one time, but that doesn't mean we were stupid or didn't deserve a complete and concise answer, or wouldn't have been able to understand one should it have been given. I can see maybe not going into detail about what the ebullioscopic constant is (or perhaps not even mentioning it at all), but to state that the only way to change the temperature of boiling water is pressure is not correct and could lead to false conclusions.

Maybe it stems from when I was younger and in math class they tell you "this is the only way to do this" only to find out a bunch of shortcuts later. I'm in favor or spelling it out up front and not hiding or omitting any information, which can and does lead to the spread of misinformation when people stumble upon the forum via searches. Hell, I've been victim to it myself, and gone around spewing lies that were told to me and I took at face value, only to find that I wasn't given the whole truth, or it was "dumbed down" to make a point.

Please don't take any of this the wrong way. I like you, I think you provide great support and information here and are a very respectable community member. Nothing against you personally. I'm just a pedant at the core.

Cheers