Boil & Evaporation Rates

[hafmpty]

I have a question about boil off & evaporation rates.

In an episode of Brew Strong, John Palmer mentions George Fix's advice that an evaporation rate greater than 15% should be avoided. I found the place in An Analysis of Brewing Techniques where Fix says this.

When I brewed 10gal batches my evaporation rate was around 13%. Because of back problems, I'm moving to brewing 2.5gal batches. With a 2.5gal batch, I don't think there is any way I can get a good rolling boil and come in under the 15% mark.

From my reading, it seems most "small batch brewers" are boiling off more than 15%. My estimates are that I will have ≈4.5gal at the start of the boil. I'm assuming my boil off rate using the same burner will be about the same, perhaps a little less. But even if I were to boil off 1gal per hour, that puts me at ≈22% for the evaporation rate.

Is this a problem? Is there anything I can do to make sure my beers don't suffer from the negative flavor & stability effects of too high of an evaporation rate?

Thanks for your help!

 

[thekraken]

I have a question about boil off & evaporation rates.

In an episode of Brew Strong, John Palmer mentions George Fix's advice that an evaporation rate greater than 15% should be avoided. I found the place in An Analysis of Brewing Techniques where Fix says this.

...

Is this a problem? Is there anything I can do to make sure my beers don't suffer from the negative flavor & stability effects of too high of an evaporation rate?

Thanks for your help!

Do you have specifics about what Palmer and Fix say the negatives are? This is a new one on me.

 

[joebob296]

Jamil also talked about this in one of his earlier podcasts. It was before September 2006, quite along time ago but I just got done listening to it.

Edit: Found it. It's Mild-The Jamil Show-08-14-06. I tried to directly link it but it's not working on mobile.

 

[hafmpty]

Do you have specifics about what Palmer and Fix say the negatives are? This is a new one on me.

Here's the info.

 

[hafmpty]

Also, here's the show: http://thebrewingnetwork.com/shows/600

 

[thekraken]

Thanks for posting that. Interesting read.

Is this text geared more toward commercial brewing?

It seems that the concern here isn't directly the amount of water boiled off but the length of time of the boil to create the maillard reactions. I'm inclined to think that on the homebrew scale, and at your typical 60-90 minute boil, that this wouldn't be a big deal. I'll be curious to see what others have to say.

Also, I'll look forward to listening to that podcast.

 

[hafmpty]

Thanks for posting that. Interesting read.

Is this text geared more toward commercial brewing?

It seems that the concern here isn't directly the amount of water boiled off but the length of time of the boil to create the maillard reactions. I'm inclined to think that on the homebrew scale, and at your typical 60-90 minute boil, that this wouldn't be a big deal. I'll be curious to see what others have to say.

The book is "brewing focused" but I wouldn't say it applies to only commercial brewing. Science is science. That's why I'm wondering what it means to my own processes. The less liquid you start with, the more the percentage of boil-off goes up.

Plus, during a "Homebrewing" specific show, (i.e. Brew Strong), Palmer quotes this book saying, your evaporation rate shouldn't be above 15%. I'm just wondering (along with you) what this means for my processes.

What I'm not looking for is anecdotal "I've never experienced negative effects...so" kind of comments. I'm looking for something beyond experience.

 

[philosofool]

The problem with excess boil off isn't really about boil-off, per se, but boil off is a correlate of excess heat that can result in more maillard recactions. A good process indicator that you're applying too much heat is boil off. Too many maillard products will be a problem in many styles of beer. You don't want a bocky IPA or pilsner; much of the published research in brewing essentially assumes you are trying to make a pale lager and you should keep that in mind whenever you read it.

However, besides heat, kettle geometry, volume, altitude, and humidity are factors in evaporation rate. Unless you are experiencing excess melanoidins, there's no reason to worry about this problem. And even if you are, wort pH and other factors may be the reason for the melanoidins.

 

[hafmpty]

The problem with excess boil off isn't really about boil-off, per se, but boil off is a correlate of excess heat that can result in more maillard recactions...Unless you are experiencing excess melanoidins, there's no reason to worry about this problem. And even if you are, wort pH and other factors may be the reason for the melanoidins.

Would you say then that as long as the wort is not leaping out of the pot, so long as it's a nice "rolling boil" that I should be fine? If the heat isn't excessive, the evaporation rate will still be high but I won't be cranking the heat and cooking the &$% out of it.

True?

 

[Derek1985]

I would think that with all other factors being scaled down and essentially kept constant from 15 gal to 5 gal, that boil off will essentially stay constant, No?

 

[joebob296]

I would think that with all other factors being scaled down and essentially kept constant from 15 gal to 5 gal, that boil off will essentially stay constant, No?

The boil off tate might stay the same. But if you boil 1 gallon from 15 that's 6%. Now boil off a gallon from a 5 gallon batch. That's around 20%

 

[Derek1985]

The boil off tate might stay the same. But if you boil 1 gallon from 15 that's 6%. Now boil off a gallon from a 5 gallon batch. That's around 20%

Of course. I meant percentage wise.

I guess the big difference would be in the size of the kettle and it's losses to the surrounding environment. I larger kettle would lose more heat to the surroundings where as a smaller kettle will have less thermal mass and therefore lose less to the surroundings. This would probably lead to an increase in boil off.

This is of course a gross generalization in the absence of hard numbers for kettle and volume size.

 

[hafmpty]

Of course. I meant percentage wise.

You didn't mean percentage...you meant volume. 1 gallon is 1 gallon. But like it was said, comparing percentages, 1 gallon lost from 5 gallons is higher (20%) than 1 gallon lost from 10 gallons (10%).

This is why the whole "percentage" thing is frustrating to me. I'm concentrating my wort, I get that...so if I don't want to concentrate my wort beyond a 15% number, then, as I approach that number, should I "add water" back in to avoid the negative effects of an over-concentrated wort?

But then, I'm creating my grain bills assuming that I'll boil off 1-1.5gal depending on the boil length. If I'm creating the maillard reactions in the boil and boiling off DMS, etc...

&#@#! I don't know. Not sure if I should care. I haven't been able to conduct a boil evaporation rate test yet on my new system (waiting for the gas hose). Maybe my boil off rate will be lower...I think it will be. But I will still probably not get close to the .65gal per 60min that is 15% of my estimated starting boil volume.

I sent emails to John Palmer and left a comment on the show at the Brewing Network site. Maybe I'll hear back. If I do...I'll let you know.

 

[thekraken]

This is why the whole "percentage" thing is frustrating to me. I'm concentrating my wort, I get that...so if I don't want to concentrate my wort beyond a 15% number, then, as I approach that number, should I "add water" back in to avoid the negative effects of an over-concentrated wort?

I think not. Here is what I'm thinking: the issue isn't concentrating the wort, it's the milliard reactions from the "thermal load". The text that you posted earlier doesn't mention the evaporation rate being the cause of the issue but the cause is the "thermal load". They use the evaporation percentage as an indirect indicator of the thermal load applied to the wort. If you were to approach the 15% evaporation and add water you still applied the same thermal load, damage was done (if any). I'm also thinking that this max 15% evaporation figure doesn't necessarily apply to our scale.

(The text says thermal loading = long boil times or high-temperature/high-pressure boils.)

I'm trying to get through the podcast you linked earlier, so far through 2 commutes I haven't gotten to the part discussing this topic yet... I'll get there.

 

[Derek1985]

&#@#! I don't know. Not sure if I should care.

You should'nt. Until....

I haven't been able to conduct a boil evaporation rate test yet on my new system....

...you do this. Your worrying about something you havent tested yet.

 

[hafmpty]

I think not. Here is what I'm thinking: the issue isn't concentrating the wort, it's the milliard reactions from the "thermal load". The text that you posted earlier doesn't mention the evaporation rate being the cause of the issue but the cause is the "thermal load". They use the evaporation percentage as an indirect indicator of the thermal load applied to the wort. If you were to approach the 15% evaporation and add water you still applied the same thermal load, damage was done (if any). I'm also thinking that this max 15% evaporation figure doesn't necessarily apply to our scale.

(The text says thermal loading = long boil times or high-temperature/high-pressure boils.)

I'm trying to get through the podcast you linked earlier, so far through 2 commutes I haven't gotten to the part discussing this topic yet... I'll get there.

I think you are right. I re-read it and that makes a lot of sense. I also found the following quote from Fix's other book (I can't find the exact reference though...it's not on the page indicated).

Principles of Brewing Science, G.Fix, pp.76:

On the other hand, excessive thermal loading (e.g. uncontrolled high-temperature [...] boils) can transform the simple melanoidins into less desireable heterocyclics [...]
The second level of complexity consist of sulfur-bearing heterocyclics. Heterocyclics and methionine products have flavour that strikingly recalls cooked cabbage.

The potential presence of these compounds in beer is responsible for the sensivity of many brewers to free SMM in wort. Nevertheless it is excesive heat treatement - not inadeqate boiling - that is responsible for their formation.

It seems to me that the HIGH HEAT applied during a boil is the cause, not the concentration...to a certain extent. The "extract twang" that extract brewers get is related to the formation of maillard reactions during the formation of the extract and the continued darkening of the wort extract that occurs over time. So when extract brewers boil very, VERY high gravity worts for 60+ minutes, it will occur more.

In my case, I'm not doing that. I'm boiling a lower gravity wort down to an "average strength" wort, not boiling a high gravity wort and then diluting it down to an average strength wort.

That's all very helpful and (honestly) the whole discussion could have been avoided if I had read a bit more carefully.

BTW...found an interesting archived post from a guy discussing the same thing.
http://www.beerandloafing.org/hbd/fetch.php?id=73856