Any downside to a low boil off rate?

[fun4stuff]

I’m going to try my new eBIAB setup today!

I have a steam condenser setup so I’ll be keeping the lid on.

Last night I did a run with just water and my boil off was 0.4 gal/hr. It may be slightly lower too, as i was still getting tweaking new set up.

Is there any downside to such a low boil off rate? Obviously my mash thickness isn’t going to be as thin as it was with my 20 gal pot/propane burner that has 2 gal/hr boil off....

 

[Qhrumphf]

As long as you're getting wort turnover and good isomerization there's no benefit to a high boiloff rate. 5% boiloff is plenty. Most homebrewers boil off more like 20%, which is overkill and ultimately bad for the beer.

 

[Robert65]

^^This. 4-6% is ideal, so long as there's circulation all you need is a simmer, and by the time you approach 10% boil off, you're damaging your wort and significantly compromising the quality of the beer.

 

[McKnuckle]

...by the time you approach 10% boil off, you're damaging your wort...

I don't really understand this in the realm of homebrewing, where boil-off rates are usually disproportionate to batch size vs. what the pros experience. When I boil for a 1 gallon batch, I start with 1.5 gallons and 0.5 evaporates. That's 33%. Am I damaging my wort even if I'm boiling gently? I wouldn't think so.

Ditto for a 2.5 gallon batch, boiling 3 gallons (16.7%). Or a 1 gallon boil-off starting with 6 gallons, yielding 5 in the fermenter (16.7%).

So it's not the rate per se; it's extreme boil vigor that I think you're proposing is harmful. Right?

 

[Robert65]

So it's not the rate per se; it's the boil vigor that I think you're proposing is harmful. Right?

Right. Thermal loading for the nerds. But I do think evaporation rate is a good index of this, though, as you point out, not a universal constant, as it is dependent on the configuration of the individual system. It's something we can learn to use pretty effectively though. Another point would be that while evaporation itself is not a primary goal, expulsion of certain undesirable volatiles is; and for homebrewers with a large surface area to volume ratio, these can be brought to the surface more readily than in a large commercial system, as long as there is good circulation in the kettle; so we can still target very low evaporation rates.

 

[mabrungard]

I don't really understand this in the realm of homebrewing, where boil-off rates are usually disproportionate to batch size vs. what the pros experience. When I boil for a 1 gallon batch, I start with 1.5 gallons and 0.5 evaporates. That's 33%. Am I damaging my wort even if I'm boiling gently? I wouldn't think so.

You're putting a great amount of energy into that wort and producing a lot of evaporation. Small HB batches typically have a high percentage of wort surface in the kettle when compared to the volume of wort. That invites a very high exchange with the atmosphere and loss of water.

You are very much better off by covering the kettle to a high degree when making a small batch. The most important factor is to create a decent rolling action in the kettle wort. Covering the kettle allows you to back off the amount of energy (turn down the heat) and it brings the evaporation losses more in line with typical brewing. Reducing evaporation loss to under 10% is a good goal and bringing it lower can sometimes be better. I now try to limit my loss to around 8%.

DMS reduction only takes a few minutes of open boiling, so don't blame high evaporation on a goal to avoid DMS in your beer.

 

[mabrungard]

Oh, sorry. I should have also responded to the OP.

Yes, there is a lower limit to boil off. I've seen a research paper that stated that they produced acceptable beer with a boil off loss of only 2%. But I'm not sure that this is a goal that most brewers accept. My understanding is that somewhere between 4 and 10 percent is a desirable loss.

Practically, if your beers do not suffer from DMS, then its possible that you're not evaporating too little.

 

[Robert65]

There's been a parallel thread going on lately: https://www.homebrewtalk.com/forum/threads/thoughts-on-boil-off-rate.674162/

In which I recommend reading Martin's article on wort boiling in the May/June 2019 Zymurgy. In case he doesn't want to blow his own horn. [emoji6]

 

[Carolina_Matt]

Interesting. With my 120V digiboil, I boil off about 0.8 gallons/hour. I typically start with 6.5 gallons before the mash, and I have about 6 gallons pre-boil. I thought 0.8 was a good boil-off rate since I have a low rolling boil that's not vigorous. But that's about 13% boil-off, which seems high.

The digiboil is 1500W. During my next batch I'll try turning off the 500W element and just keeping the 1000W element. If it can keep a rolling boil, maybe I'll do that going forward. Although I thought 1500W was already borderline, so 1000W might not be enough.

 

[Special Hops]

I'm sorry I do not agree with boiling with the lid on. Boiling gets rid of off flavors like DMS that evaporate of with the boil. If you keep the lid on or even partially on, it will condense on the lid and end up back in your beer.

I keep the lid on while bringing it to boil, then when it's boiling, lid comes off and I crank down the heat to where it's just above simmering, just enough to make sure there is good movement and turnover of the wort.

 

[Vale71]

I don't really understand this in the realm of homebrewing, where boil-off rates are usually disproportionate to batch size vs. what the pros experience. When I boil for a 1 gallon batch, I start with 1.5 gallons and 0.5 evaporates. That's 33%. Am I damaging my wort even if I'm boiling gently? I wouldn't think so.

You can't be boiling gently and lose 33% (as an hourly rate) to evaporation. For every kilogram of water you turn to steam you need to transfer 2257 kiloJoule to your wort. You cannot halve that and still have the same evaporation rate. In other words, boil vigor and evaporation rate are inextricably linked to thermal loading of the wort.

With commercial systems the lower limit of 4% has indeed been breached in trials. The issue with that however is that the result vis-a-vis DMS elimination becomes critically dependent on the DMS-P level of the malt employed. As this varies from batch to batch (and is directly linked to DMS-P levels in barley) and from year to year it's possible for such a system to become unusable during particularly bad years, when no malthouse can actually supply malt conforming to the extremely low DMS-P levels required by such a system. For a commercial operation needing to shut down for a year would mean instant bankruptcy and so it would be really hard to find buyers willing to take on such a huge risk.

 

[Vale71]

I’m going to try my new eBIAB setup today!

I have a steam condenser setup so I’ll be keeping the lid on.

Last night I did a run with just water and my boil off was 0.4 gal/hr. It may be slightly lower too, as i was still getting tweaking new set up.

Is there any downside to such a low boil off rate? Obviously my mash thickness isn’t going to be as thin as it was with my 20 gal pot/propane burner that has 2 gal/hr boil off....

What's your boil volume? 0.4 hal/hr is meaningless without knowing the actual rate in percent. Also what's the power rating of your heating element?

 

[bracconiere]

Interesting. With my 120V digiboil, I boil off about 0.8 gallons/hour. I typically start with 6.5 gallons before the mash, and I have about 6 gallons pre-boil. I thought 0.8 was a good boil-off rate since I have a low rolling boil that's not vigorous. But that's about 13% boil-off, which seems high.

The digiboil is 1500W. During my next batch I'll try turning off the 500W element and just keeping the 1000W element. If it can keep a rolling boil, maybe I'll do that going forward. Although I thought 1500W was already borderline, so 1000W might not be enough.

i can boil 7 gallons with, according to my kill-a-watt meter and fan speed controller, 600-700 watts.....

 

[doug293cz]

I'm sorry I do not agree with boiling with the lid on. Boiling gets rid of off flavors like DMS that evaporate of with the boil. If you keep the lid on or even partially on, it will condense on the lid and end up back in your beer.

I keep the lid on while bringing it to boil, then when it's boiling, lid comes off and I crank down the heat to where it's just above simmering, just enough to make sure there is good movement and turnover of the wort.

DMS has a boiling temp range of 95°F to 106°F. So unless the lid and kettle walls are 106°F, or lower, DMS will not condense on them. A small opening is all that is needed for the DMS to escape the headspace in the covered kettle. You need temps near 212°F in order to convert SMM into DMS at a rate high enough to get rid of most of the SMM within a 1 hour, or so, boil time. You also need some circulation in the hot wort in order to bring the created DMS to the surface where it can escape.

Brew on

 

[fun4stuff]

What's your boil volume? 0.4 hal/hr is meaningless without knowing the actual rate in percent. Also what's the power rating of your heating element?

During my boiling trial it was 6 gallons. Boiled for 2 hrs and took avg gal/hr from that. I was still tweaking the water flow rate on the steam condenser and how many watts i was using to boil with.

240v 3500 watt digiboil. I was able to keep a pretty good rolling boil with just 1000 watts.

I’m going to start BIAB brew in just a min. Starting volume is 6.5 gallons. End volume will hopefully be around 5.5 gal.

 

[Qhrumphf]

DMS has a boiling temp range of 95°F to 106°F. So unless the lid and kettle walls are 106°F, or lower, DMS will not condense on them. A small opening is all that is needed for the DMS to escape the headspace in the covered kettle. You need temps near 212°F in order to convert SMM into DMS at a rate high enough to get rid of most of the SMM within a 1 hour, or so, boil time. You also need some circulation in the hot wort in order to bring the created DMS to the surface where it can escape.

Brew on

Not to mention that modern malts, Pils malts included, have negligible SMM in the first place. And apart from Pils malts, it's virtually non-existant. Completely covered boils (apart from a steam stack with condensate drip catch) have been common commercially for some time.

 

[Vale71]

That's 6.6% hourly boil-off rate which is just about right. You don't really need more than that unless you actually experience problems with DMS in your beers.
You also have a very high yield of about 95% certainly in part thanks to the condenser. Are the kettle walls insulated as well?

 

[Robert65]

DMS: The monster that isn't hiding under your bed... [emoji6][emoji482]

 

[BrewnWKopperKat]

I don't really understand this in the realm of homebrewing, where boil-off rates are usually disproportionate to batch size vs. what the pros experience. When I boil for a 1 gallon batch, I start with 1.5 gallons and 0.5 evaporates. That's 33%. Am I damaging my wort even if I'm boiling gently? I wouldn't think so.

FWIW, for my 1.5 gal boils, I'll boil off about 0.25 gal (or about 15% per hour). when I boil at "level 1" / "simmer" [1]. Lid is either on or left slightly open.

[1] Boiling Wort Visual Reference

 

[fun4stuff]

That's 6.6% hourly boil-off rate which is just about right. You don't really need more than that unless you actually experience problems with DMS in your beers.
You also have a very high yield of about 95% certainly in part thanks to the condenser. Are the kettle walls insulated as well?

Kettle walls are not insulated. I have one of those neoprene jackets on it.

 

[Vale71]

That counts as insulation...

 

[stevehaun]

I use a steam condenser on my BK and I evaporate about 0.5 gal/hr (~3.5% for me). When I brew a pils, I can smell the DMS in the condensate running into my sink. The smell of DMS disappears between 40 and 60 min into the boil. YMMV.

 

[McKnuckle]

What are the supposed negative effects of boiling even at a medium vigor? My 0.47 gal/hr boil-off rate is about equivalent with my 2.5 and 1 gallon batches, in different vessels with a similar diameter. I don't boil particularly vigorously, but I do like to see a little roll at the surface. What am I missing out on? I haven't noticed anything lacking in foam, head retention, mouthfeel, clarity, flavor, etc. What should I be watching for?

 

[BrewnWKopperKat]

What are the supposed negative effects of boiling even at a medium vigor?

The May/June 2019 Zymurgy article that @Robert65 mentioned is a good source of current information on boiling boil.

 

[Vale71]

Not to mention that modern malts, Pils malts included, have negligible SMM in the first place. And apart from Pils malts, it's virtually non-existant. Completely covered boils (apart from a steam stack with condensate drip catch) have been common commercially for some time.

Not really. DMS precursors come from barley and no DMS-P varietal has been developed yet. Particularly with very pale continental malts this could still be an issue.
Covered boil vessels are certainly the norm in large commercial systems but they are designed in a way (mostly through proper insulation which saves energy as well) that there will be nearly no condensation forming before the steam condeser so you cannot really compare them to a simple lid on a pot.

 

[RM-MN]

One of the problems with a low boil off that you hadn't accounted for before the boil is more beer than planned.

 

[doug293cz]

With lower boil off, you will get a minor reduction in lauter efficiency, and therefore also mash efficiency. For any given lauter process, lauter efficiency is a function of Grain_Bill_Weight / Pre-Boil_Volume. To maintain a constant post-boil volume, your pre-boil volume has to go down if your boil off goes down. You will also need to increase the grain bill slightly to maintain the same OG, since you won't be concentrating the wort as much during boil.

For example: A 10 lb grain bill with 1 gal boil off, single sparge, 5.5 gal post boil, 0.12 gal/lb grain absorption, and 100% conversion efficiency , has a pre-boil volume of 6.5 gal, lauter efficiency of 87.45% and an OG of 1.0565. If we drop the boil off to 0.5 gal, then pre-boil is 6.0 gal, lauter efficiency is 86.11%, and OG is 1.0556.

In order to get the same OG with the lower boil off, the grain bill needs to be increased to 10.2 lb, and lauter efficiency drops to 85.73%

These are small effects, and might not even be detectable with the accuracy of typical homebrewing measurements. But, real pendants want to know.

Brew on

All calculations done with this spreadsheet

 

[Qhrumphf]

With lower boil off, you will get a minor reduction in lauter efficiency, and therefore also mash efficiency. For any given lauter process, lauter efficiency is a function of Grain_Bill_Weight / Pre-Boil_Volume. To maintain a constant post-boil volume, your pre-boil volume has to go down if your boil off goes down. You will also need to increase the grain bill slightly to maintain the same OG, since you won't be concentrating the wort as much during boil.

For example: A 10 lb grain bill with 1 gal boil off, single sparge, 5.5 gal post boil, 0.12 gal/lb grain absorption, and 100% conversion efficiency , has a pre-boil volume of 6.5 gal, lauter efficiency of 87.45% and an OG of 1.0565. If we drop the boil off to 0.5 gal, then pre-boil is 6.0 gal, lauter efficiency is 86.11%, and OG is 1.0556.

In order to get the same OG with the lower boil off, the grain bill needs to be increased to 10.2 lb, and lauter efficiency drops to 85.73%

These are small effects, and might not even be detectable with the accuracy of typical homebrewing measurements. But, real pendants want to know.

Brew on

All calculations done with this spreadsheet

While you're not wrong, I look at lowering the boiloff rate as not changing efficiency as the same preboil volume is collected, but a higher volume of wort is collected into the fermenter at lower gravity. Two sides of the same coin though.

 

[InspectorJon]

This does not make sense to me, thinking about boil off as a percentage. If my system boil off rate is .75 gal/hr at a minimal surface roll and I start with 7 gallons I get 6.25 gallons after one hour. If I start with 4 gallons I get 3.25 gallons after one hour. Same boil off rate but much different percentages.

 

[Vale71]

To get the same boil off rate as absolute quantity you need to be supplying the same amount of energy per hour. In an electric system that would mean employing a heating element with the same power rating or if brewing with gas a burner with the same rating and so on.

Now would you expect to have similar results regardless of whether you're boiling 5 gallons or 50 gallons with the same absolute boil off rate? Even intuitively it must be obvious that this cannot be the case since with 5 gallons you will get a rolling boil but with 50 you'd hardly notice the wort was boiling at all.

That is the reason why boil off rate must always be regarded as a ratio in order to make it independent of total volume.

 

[InspectorJon]

I have a 7 gallon kettle. It takes a lot of energy to get the contents up to boiling temperature. Obviously more energy with a larger volume of liquid. Once it reaches a boil I turn the heat down to maintain minimal surface rolling but still boiling, simmering one might say. If I start with six gallons of wort I can see where it would take more heat heat energy to keep it simmering than with a lesser amount of wort but it is still going off at a rate of .75 gallons/hour with that level of simmering. If I put half as much, three gallons, of wort in and maintain the same simmer activity admittedly it should take less energy but it is still going of at a rate of .75 gallons/hour. If I lower the energy input enough to end up with only .375 gallons per hour evaporation I don't think it would be boiling at all.

So what is the significance of aiming for a certain percentage of boil off rather than a certain rate of boil activity?

 

[Carolina_Matt]

i can boil 7 gallons with, according to my kill-a-watt meter and fan speed controller, 600-700 watts.....

I brewed a batch today and turned off the 500W element when I reached a boil. So I used 1000W instead of 1500W. My boil-off used to be about 0.8 gallons/hour, but it was only 0.5 gallons today. With 6 gallons pre-boil, that's an 8.33% rate. I'll go with this from now on.

I may be able to get away with just the 500W element if the kettle is partially covered, but I was happy with how things went today. There was a simmer on the surface of the wort, but it wasn't a rolling boil.

 

[bracconiere]

I brewed a batch today and turned off the 500W element when I reached a boil. So I used 1000W instead of 1500W. My boil-off used to be about 0.8 gallons/hour, but it was only 0.5 gallons today. With 6 gallons pre-boil, that's an 8.33% rate. I'll go with this from now on.

I may be able to get away with just the 500W element if the kettle is partially covered, but I was happy with how things went today. There was a simmer on the surface of the wort, but it wasn't a rolling boil.

when i boil at those wattages i mentioned, it is covered

 

[pricelessbrewing]

Not to mention that modern malts, Pils malts included, have negligible SMM in the first place. And apart from Pils malts, it's virtually non-existant. Completely covered boils (apart from a steam stack with condensate drip catch) have been common commercially for some time.

I've heard this repeatedly, and I do believe it's true, but do you have a source for this? I've never seen SMM listed on a maltster spec sheet.

 

[mabrungard]

I've never seen SMM listed on a maltster spec sheet.

Yeah, I don't recall seeing SMM content. But I'm not going so far as saying that Pils malts have less content than before. Maybe maltsters have finally perfected a way to malt and kiln a Pils malt that reduces the SMM content, but there is a lengthy study conducted in the 80s or 90s that documented how it was essentially impossible to end up with a pale enough malt AND low SMM content. They found that just kilning a couple lovibond darker could really make a substantial SMM reduction. So unless you really need a really pale colored beer, using a pale ale malt (say 3L to 5L) can make a notable difference in SMM and DMS compared to using pils malt (1.2L to 2.5L).

Therefore, I'm leery of NOT doing anything to address DMS in beers with high pils content. A period of covered simmering followed by a period of open boiling is still needed based on my research and experience.

 

[pricelessbrewing]

Yeah, I don't recall seeing SMM content. But I'm not going so far as saying that Pils malts have less content than before. Maybe maltsters have finally perfected a way to malt and kiln a Pils malt that reduces the SMM content, but there is a lengthy study conducted in the 80s or 90s that documented how it was essentially impossible to end up with a pale enough malt AND low SMM content. They found that just kilning a couple lovibond darker could really make a substantial SMM reduction. So unless you really need a really pale colored beer, using a pale ale malt (say 3L to 5L) can make a notable difference in SMM and DMS compared to using pils malt (1.2L to 2.5L).

Therefore, I'm leery of NOT doing anything to address DMS in beers with high pils content. A period of covered simmering followed by a period of open boiling is still needed based on my research and experience.

Thanks Martin. So would the same apply to things like "extra pale ale malt" that's sub 3L?

 

[Robert65]

Maybe maltsters have finally perfected a way to malt and kiln a Pils malt that reduces the SMM content, but there is a lengthy study conducted in the 80s or 90s that documented how it was essentially impossible to end up with a pale enough malt AND low SMM content.

Kunze discusses modern malting practices manipulating kilning times and temperatures to achieve color below 4 EBC, SMM not exceeding 4-5 ppm dry basis, and still keeping TBA below 15. He indicates that maltsters are now expected by brewers to deliver this sort of malt, as they demand to be able to achieve acceptable DMS levels with their modern, limited, boiling methods. It seems that the responsibility for control of DMS has been largely shifted from brewer to maltster. In German commercial practice the critical focus in the brewhouse is not boiling, chasing one's tail trying to form and evaporate DMS, but rapid cooling to avoid further thermal splitting of SMM. This is an area homebrewers could benefit from giving more priority. If conducting a whirlpool, it is critical to cool the wort to below 185°F immediately after ceasing boiling and before commencing the whirlpool stand. At this point no more DMS will form, and any free DMS remaining will be scrubbed out in fermentation.

 

[Qhrumphf]

I've heard this repeatedly, and I do believe it's true, but do you have a source for this? I've never seen SMM listed on a maltster spec sheet.

Sitting through enough maltster presentations at conferences. As @Robert65 said, there's an understanding by maltsters that low DMS potential is an expectation of brewers purchasing malt.

And Pils malt certainly does have higher DMS potential than darker base malts, wasn't trying to imply that it didn't. Rather that a 60 min boil with 5% boil off and a means to keep DMS condensate out is plenty. The open roaring volcanic 90 min homebrew boil is patently unnecessary. I don't treat Pils malt wort any differently than I treat any other wort.

 

[mabrungard]

Thanks Martin. So would the same apply to things like "extra pale ale malt" that's sub 3L?

Nomenclature! Malt names have little to do with their color. I’ve tried to categorize malt in respect to it’s practical usage. Pils malt is less kilned than the malts typically used to brew beers that don’t need to very light which I’ve termed Pale malt.

It’s sad that maltsters use confusing and conflicting terms.