Dealing With Kettle Evaporation

[brendanos]

Ecosse would be better of boiling for the first 20 or so minutes with the lid off (allow the DMS to escape). Then partially covering the remaining boil.

Or conversely it may be more effective to leave the lid off for the last 20 minutes, as while the liquid is at boiling temperatures, additional DMS/precursors can be generated/converted to DMS.

 

[Thirsty Boy]

I'm with Kai,

Lid partially on for the whole boil will be fine, just fine. Close or open the gap till you are happy with your evaporation rate, but make sure that you are boiling off at least 8-10% of you starting wort volume, then you will be fairly sure that you have driven off all the volatiles (DMS etc) that need to be driven off.

Just to reassure you - I tried to find a picture of a commercial boil kettle that was open at the top - not so much luck. I'm sure I could have fouind one if I kept looking, but strangely, they mostly all seem to look roughly like this - with a definite lid like structure.

 

[Justin]

Hi Ecosse.

Just a quick question regarding your evapouration rate, are you sure it's all evaporation rate you are calculating? Here's the thing.

Your preboil volume is 27L (hot), target after boil volume is 19L (cold- +4% thermal contraction). You get 16L into your fementer. How much wort (with all the hops and trub) is left in your kettle after you drain off to the fermenter? I'll bet ~3L or maybe more, especially with a 60L kettle with a wide flat bottom-makes it very hard to drain the last bit of clear wort.

Sounds to me like you are calculating your losses into the fermenter as well in your calculations for evapouration rate (ie. kettle dead space if you will). Next time, pour all that last final cruddy, trubby wort into a jug and measure how much volume you have left.

This is how I do it. I factor my batch size for what's in my kettle at the end of the boil. eg. My batch sizes are generally 28L. At the end of the boil I have 28L of wort at the correct gravity in my kettle. I now drain that into my fermenter and I get anywhere between 23-25L actual wort in the fermenter -at the target OG. But the batch size was calculated at 28L and I made hop additions, grain additions etc for a recipe size of 28L batch. It's just that I lose 3-5L of that 28L to trub and hop pellets in the bottom of the kettle at the end of the boil. I hope you follow. The evapouration rate is actually the difference between preboil volume and post boil volume, not volume in fermenter.

As a side note, what was your preboil gravity of the wort? What was the final gravity post boil (this should have been the gravity of the 16L in your fermenter? Ok, so now what was your gravity after you added water to 19L? It is possible that you actually diluted your beers OG gravity a little by adding that water. For me having the correct OG is more important to me than having my full final volume because I made all my hop additions and bitterness calculations with a particular OG in mind.

Anyway, let me know.

Cheers, Justin

 

[Ecosse]

Hi Justin,

Thanks for the reply.

Just a quick question regarding your evapouration rate, are you sure it's all evaporation rate you are calculating? Here's the thing.

Your preboil volume is 27L (hot), target after boil volume is 19L (cold- +4% thermal contraction). You get 16L into your fementer. How much wort (with all the hops and trub) is left in your kettle after you drain off to the fermenter? I'll bet ~3L or maybe more, especially with a 60L kettle with a wide flat bottom-makes it very hard to drain the last bit of clear wort.

Sounds to me like you are calculating your losses into the fermenter as well in your calculations for evapouration rate (ie. kettle dead space if you will). Next time, pour all that last final cruddy, trubby wort into a jug and measure how much volume you have left.

Yep I was worried about this too, so on the second brew I measured what was left in the kettle and it was just 300ml. I use a Hopsock from Craftbrewer and pull the mushed hop pellets out before draining the kettle. The kettle itself is fitted with a pickup tube which works remarkably well considering I made it . All that's left is the protein gunk and even that gets sucked out if I'm not careful.

This is how I do it. I factor my batch size for what's in my kettle at the end of the boil. eg. My batch sizes are generally 28L. At the end of the boil I have 28L of wort at the correct gravity in my kettle. I now drain that into my fermenter and I get anywhere between 23-25L actual wort in the fermenter -at the target OG. But the batch size was calculated at 28L and I made hop additions, grain additions etc for a recipe size of 28L batch. It's just that I lose 3-5L of that 28L to trub and hop pellets in the bottom of the kettle at the end of the boil. I hope you follow. The evapouration rate is actually the difference between preboil volume and post boil volume, not volume in fermenter.

I reckon, in my own haphazard way, I've been trying to do this as well, I'm just working on small volumes (American recipe sizes until I've a bit more confidence). I've got a rod notched with volume marks that I use to measure the pre and post boils and that's where I'm seeing the problem.

As a side note, what was your preboil gravity of the wort? What was the final gravity post boil (this should have been the gravity of the 16L in your fermenter? Ok, so now what was your gravity after you added water to 19L? It is possible that you actually diluted your beers OG gravity a little by adding that water. For me having the correct OG is more important to me than having my full final volume because I made all my hop additions and bitterness calculations with a particular OG in mind.

Surprisingly I've been pretty happy with my gravities so far. I've been a smidgen over each recipe's pre-boil OG (and also what Beersmith reckons I should have based on the grain bill) with about the right amount of liquid after the batch sparge. Using the Boiloff calculator in Beersmith (or bothering to do it by hand) says that boiling down to 19L would make the gravity just about spot on. The gravity on the 16L was very high, diluting it to 19L brought it back to each recipe's anticipated post-boil OG.

Cheers.

 

[Justin]

Ok, sweet. Sounds like you are on top of it.

Just thought I would raise that possibility as it was something i struggled with when I was first starting all grain. Sounds like you are genuinely getting a pretty high boil off so hopefully some of the other ideas above should be the answer. I dont think you should need a new burner if you can turn it down to a gentle rolling boil.

FWIW I use the dipstick for measuring my volumes and it's never let me down yet Work great and so easy to clean.

All the best, Justin

 

[Ecosse]

Ok, sweet. Sounds like you are on top of it.

Just thought I would raise that possibility as it was something i struggled with when I was first starting all grain. Sounds like you are genuinely getting a pretty high boil off so hopefully some of the other ideas above should be the answer. I dont think you should need a new burner if you can turn it down to a gentle rolling boil.

FWIW I use the dipstick for measuring my volumes and it's never let me down yet Work great and so easy to clean.

All the best, Justin

Thanks for that.

I reckon I'll give it a year before I'll decide if I'm on top of it. . The whole brew day still feels like a barely controlled explosion. Terrific fun though.

I reckon I might try the lid idea just to cut down on evap a wee bit.

 

[drsmurto]

Doesnt sound over the top to me. I have my boil off set to 15% which means i have a pre-boil volume of 29.5L and after 90 mins and 1L lost to trub i have 20L in the fermenter. I like to boil quite vigorously for the first 30 mins and then wind it back down for the next 60 mins. Think i read something about this on here.... something to do with less haze, clears better or some such malarky

 

[SpillsMostOfIt]

...

I like to boil quite vigorously for the first 30 mins and then wind it back down for the next 60 mins. Think i read something about this on here.... something to do with less haze, clears better or some such malarky

I recall the same malarky but fail to remember where it came from. I boil like crazy until I add my flavour hops, then tone it down a bit for the balance of the boil.

Like everything else, it may not work for everyone, but it does for me.

 

[tim_mortensen]

I am yet to be convinced that high evaporation is bad, although there are opinions to the contrary, or that wort can be caramelized with 16 l left in the kettle. I can maybe believe that Maillard reactions are slightly increased in the boil. Assuming you are batch sparging, I would sparge some more, and add water during or after the boil, and enjoy the good hop utilization, and clear beers that result.

Was just reading the chapter on Wort Boiling by Fix this morning. Apparently excessive thermal loading from uncontrolled high temperature boils can transform the melanoidins into sulphur-bearing heterocyclics, which produce a cooked cabbage flavour in the beer. So boiling is the balance between elimination of DMS and reducing the production od heterocyclics.

"...A general rule is that the volume reduction be at least 7%. However, it has been shown that evaporation rates above 12% may produce level 2 heterocyclics, leaving vegetal malt tones that are accompanied with some astringency. A wide range of level 2 and 3 heterocyclics is possible once evaporation rates exceed 15%"

That said, my evaporation rate is generally about 15% using a 50L stockpot, and I get neither DMS or cabbage flavours in my finished lagers. Though I do keep the boil at a fairly modest level

Tim

 

[Kai]

Kai,

I wonder about your logic.

If only 1% escapes as steam, then 99% falls back in.

Ecosse would be better of boiling for the first 20 or so minutes with the lid off (allow the DMS to escape). Then partially covering the remaining boil.

Personally, I would get a bigger mash-tun and boiler and do bigger batches or as Tony said, turn the gas down a tad.

cheers

Darren

Darren,

my logic was that if the evaporation rate with the lid off is, say, 4 times too high then leaving the kettle 1/4th uncovered would allow a more 'normal' evap rate. Any DMS that recondenses and drips back into the kettle will probably make it out that 1/4 gap over the duration of the boil.

As brendanos says, I wouldn't want to boil covered for the latter part of the boil for risk of further DMS formation from SMM. But yes, overall I'd rather just turn the juice down a bit.

 

[braufrau]

I had a similar problem.
I boil my small kettle on the stove, across 2 burners.
Now I boil on 2 burners for 15 mins and then turn the smaller one off.
I get lots of hot break and no DMS so ...
You could do something similar.