I am sure there is no clear cut answer. I live in the Denver area at about 6,000 ft in elevation so I think our boil off would be even higher. I use beer smith, but yesterday I brewed a 5 gallon batch of All grain and used 15% as evaporation rate, 3/4 gallon as loss to trube and 4% as cooling loss which are settings I have used previously. Beer Smith said I should have a pre-boil volume of 7.01 gallons with the above variables, but I was left with just a little over 4 gallons of wort in my fermentor which is the first time I was that far off.
Two things were different with this batch: I used a Chillus Convolutus wort chiller from Morebeer instead of an immersion chiller and Blichmann’s hopblocker. Both pieces of equipment worked great. Does anyone have any insight as to why I might have lost 3 gallons of wort with a 60 minute boil? Does the vigor of the boil matter much? Thanks very much.
Elevation, of course, is a big factor. At “normal” elevations, it’s typical to boil off about a gallon over 60 minutes, but in Colorado, I would expect this to be closer to maybe 1.5 gallons or something like that (I’m not sure). But if as you say, this is the first time you were so far off, maybe this wasn’t the biggest factor for you. Just something to be aware of in your boiloff estimates.
Another big thing is the wort lost in the hot and cold break. Is it really 0.75 gallons? For me it’s much less, for others it could be that much or more.
And in similar fashion, what about hops? If you normally don’t use a ton of hops, but this time around you went crazy and used 12 ounces of hops or something like that, they will soak up a TON of wort, especially if you used whole hops instead of pellets. This can knock your volume way down.
Humidity is another one. Your boiloff rate will be huge if the humidity is only 20%, versus very slow on a muggy summer day when the humidity might be 90%. This can have a big impact.
There are probably dozens of other factors. We don’t have all the information here on the web, so you will need to take the time to backtrack every single step of the way to nail it down. And even then, it might not be easy.
Boil off is going to depend on the humidity (if you’re outside), boil vigor, and most importantly the surface area of your pot. People here generally seem to think measuring it as gallons per hour makes more sense. In my wide 20 gallon pot, I boil off 2 gallons per hour whether it is completely full or half full. You’re going to have to measure the typical rate for your system, but it will go up on dry days.
I don’t use it either. I use Beer Alchemy, because at the time it was the only program that would run on a Mac, and Beer Alchemy doesn’t calc the absorption automatically but has a calculator. Nevertheless, absorption would account for around 1.25 gallons missing in a 10# grain bill.
Does someone who uses BeerSmith know if it automatically accounts for the absorption of water into the mash?
My boil-off rate actually decreased when I moved up here. I’m guessing the reduction in boil temperature more than offsets any effect from low atmospheric pressure.
As an engineer, that does not make any sense to me at all. Lower atmospheric pressure should get you faster boiloff. The fact that the boiling point is lower at high elevations is all the more reason of why it boils off faster – you don’t need to add as much heat to get it to vaporize. But in reality, you’re no doubt using the same burner as you used elsewhere, so you’re adding the same amount of heat as always. So… faster boiloff. If not, then there’s something else going on that you’re not aware of or not telling us.
Ack… it’s like I said… there’s too many variables. I wonder if you’re seeing an offset due to humidity or something.
It doesn’t make any sense to me either, but I can’t think of any other variables that have changed. Average temperature and humidity are lower here too, so I would have expected a pretty significant increase in boil-off rate.
The heat of vaporization increases with a decrease in temperature, IIRC. I doubt that it’s enough to explain the drop I’ve seen (25%) though.
If you are using a propane burner, it is getting less O2, correct? Need to put a turbocharger on it. Classic solution for combustion engines at high altitude.
Hah! Good point about less O2 Jeff, so maybe the propane is burning less efficiently. Interesting to think about, but like Dave said, too many variables. I’m sure someone knows the values to plug in to that equation, but it’s not me.
Good point. I’ve been assuming that a 30% reduction in pressure isn’t enough to result in incomplete combustion of the propane, but that’s only because the amount I use per brewday has stayed more or less constant.
I’m also in the Denver area and I typically get 1.5 - 2.5 gallons per hour evaporated during the boil. Your boil off rate is probably not noticably impacted by humidity, ambient temperature, air pressure, or liquid surface area, except where those parameters might impact the efficiency of transferring heat from your heat source to your wort. However, all of these parameters can be in play during the times you’re not actually boiling, like when you are heating to a boil, or when you’re chilling. If you’re getting a lot of undesired loss at these times, you may want to cover your pot. But watch out for boilovers!
Can you provide more details on the wort volume through your brewing process? You say BeerSmith calculated you should have a 7 gallon pre-boil volume. How much water did you use for mashing and sparging? What did you actually measured in your brew pot after lautering? What was the volume after cooling? Without those step-by-step details we’re just guessing at where the lost wort went.
For me, the usual culprit of lost wort after cooling is the hops. How much did you use, and were they whole or pellet? If whole hops, did you bag the hops and squeeze out the wort as the Blichmann hopblocker web page suggests?
If the majority of the wort was lost in the boil then I think boil vigor is the cause. Lower ambient pressure only means lower saturation (boiling) temperature, the heat of vaporization doesn’t change significantly. Hence higher altitude means you’ll reach a boil quicker compared to sea level but the rate of boiling won’t change significantly assuming constant heat input. Regardless of humidity or other external factors, boil vigor is the only variable you have control over so it you’re losing volume to the boil try turning down the burner.
Be careful trying to target a specific volume though, you should really be after a target gravity. That depends on your mashing and lautering, the boil is more about concentrating the wort into the gravity you desire. If you end up with 5 gallons of 1.040 beer and you wanted 5 gallons of 1.050 beer, that’s not the boil or hops, that’s your lautering.
Lastly - I usually end up with about 1/2 gallon less than I expect once I’m done bottling. No matter how many notes and measurement points I take I still can’t account for the loss. I suspect it’s loss to the trub since that’s difficult to measure. Rather than chase my tail trying to eke out the details of my system I usually aim for 5.5 or 6 gallons, expecting I’ll end up with roughly 5 in the end.
Hello DMS, IMO, covering your boil may lead to bad flavors. Here in BFE, WYO, I experience around a gallon
per hour in my boils and my elevation is at 1 mile above sea. The time I had water issued like you describe,
I attributed it up to error…now that I am dialed in with my system, Water quantities are apparent.
