.....could we brew in a pressure cooker?
Lid on or off during boiling?
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strange-steve
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True but in high gravity beers a short sparge is required in order to hit a high pre-boil gravity, so a higher boil-off rate means you can have a lower pre-boil gravity, which means you can sparge longer, which can give a big jump in efficiency.
...my head is cabbaged now!
Drunkula
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Yep - and I was going to do it until I found out it had already been done.
What was the outcome?
Drunkula
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Really fast turnout and really good beer.
https://www.evensi.com/beer-ecofriendly-pot-brew-grain-glass-5-days/313172280
Beer?
I boil with it off but my lid has a small hole for one of them recirculating thingy pipes, i will just leave it off
Hi, OK I'm blaming you lot for me ending up reading this technical article on DMS at 7:15 this morning since I was pretty sure phase equilibria of volatile solutes would mean the evaporation behaviour was a bit different from expected. If you really want your mind boggled at the maths then try this paper:
https://onlinelibrary.wiley.com/doi/pdf/10.1002/jib.301"Evaporation behaviour of DMS in an aqueous solution at infinite dilution – a review"
The short version is that things dissolved in lots of solution have a boiling point a lot closer to the solvent depending on the dilution behaviour. Eg salt water boils only at a teeny bit higher temperature despite lots of salt - 58 g in a litre for 0.5 C rise (at sea level atmospheric pressure).
Due to dilution DMS does not change the boiling point of the wort, so it won't boil off until 100deg, though a small amount will be lost at a lower temperature but only in the same water vapour also lost at that temperature. The effect of this is that it takes a lot longer than you would initially expect to remove the DMS. In addition the vapour pressure of DMS is higher than water so the water will preferentially condense, such that with a vented lid, the lid would be expected to preferentially condense the water to DMS but not entirely. The following paper demonstrates that the DMS on it's own is mostly removed after 20 mins of boil.
https://onlinelibrary.wiley.com/doi/epdf/10.1002/j.2050-0416.1979.tb06845.x"Control of the Dimethyl Sulphide content of beer by regulation of the copper boil"
However this also shows that the free DMS from the mash is far less of a problem than the DMS precursors that are converted to DMS during the boil. Due to this combined effect, only about half the DMS is boiled off after an hour. To further complicate things, more DMS is formed while the wort is cooled to pitch temperature while the wort is still hot but not boiling.
One of the key findings here was that for a half hour boil, the levels of DMS could be higher than the initial amount due to the precursor conversion due to the time the wort stays hot. The total amount of DMS at pitching is little different from the amount in the mash wort but the SMM precursor is a lot reduced.
So the take aways:
1) Boiling doesn't get rid of all the DMS but does reduce it's potential formation during fermentation
2) DMS is released at a near constant rate during the whole time of the boil, and a bit more is released at a rolling boil than a simmer
3) The most critical part for DMS formation is the time taken to cool the wort.
4) Due to vapour pressure more DMS than water will be lost in partial condensation, however some of the DMS formed during the boil will be constantly returned to the wort throughout the boil.
so... if you want to reduce DMS Boil with the lid off, boil vigorously either throughout the boil or at the end of the boil, and cool quickly.
Anna
[Small edit to correct a typo in the last sentence]
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Wow...! Thanks - so things are a lot more complex than I thought; fascinating...
OK good reason to use the counterflow chiller
Outstanding, thanks for this. I have a 550m³/hr extractor fan and a very short, pretty well-insulated duct run but I still have some problems with condensation on a cold day with a vigorous boil (5.5KW element). I have been wondering if there are ways to reduce the amount of steam produced by keeping the lid on for some/all of the boil, and in fact, boil kettles with a 1.5" tri clamp ferrules seem to me to have perfect built-in chimneys :)
Next time I'm feeling brave I'm tempted to try to modify my approach and only boil with the lid off for the first 20 mins and see if it makes any difference. It should save a good deal of power too. Though I get what you mean about chilling quickly, at least that's a variable that most of us will be able to keep almost constant, although we would need to factor in the extra post-boil volume not driven off, so chilling may take a fraction longer.
My take away was that the first 20 min is only the boil off of free DMS and that it is constantly being formed from SMM, so the amount of free DMS in hot wort at the end of the boil is actually not a lot lower than at the start. The part when the boil should be at its most vigorous and lid off should be the last 20 mins not the earlier part. That would take advantage of clearing the free DMS that might have condensed back into the wort during the earlier boil.
Anna
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Ah, yes, I misread, I see now. OK well either works just as well from a practical standpoint I suppose. Cheers!
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Acronyms.
Don't you just love em
Don't you just love em
I attach an article from the Institure of Brewing and Distilling website on wort boiling and volatiles stripping:
http://www.ibdlearningzone.org.uk/article/show/pdf/697/Essentially, it is a question of taste - evaporation strips out undesirable volatiles, such as di-methyl sulphide (DMS) and its pre-cursor S-methyl methionine (SMM). DMS can give beer a “vegetable” taste, particularly noticeable in lower-hopped beers like lagers. SMM is present in barley and forms DMS when wort is hot so continues to form throughout the boil and during whirlpooling. Other undesirable flavour compounds include some aldehydes, esters and higher alcohols. In commercial breweries, the kettle has a stack venting to atmosphere or some other method for stripping undesirable volatiles from the wort.
Logically, if your beer tastes how you want it to taste, it doesn’t matter whether you boil with your lid on, off or somewhere in between but if you are getting certain off-flavours then removing or partly removing the lid may help remove them.
http://www.ibdlearningzone.org.uk/article/show/pdf/697/Essentially, it is a question of taste - evaporation strips out undesirable volatiles, such as di-methyl sulphide (DMS) and its pre-cursor S-methyl methionine (SMM). DMS can give beer a “vegetable” taste, particularly noticeable in lower-hopped beers like lagers. SMM is present in barley and forms DMS when wort is hot so continues to form throughout the boil and during whirlpooling. Other undesirable flavour compounds include some aldehydes, esters and higher alcohols. In commercial breweries, the kettle has a stack venting to atmosphere or some other method for stripping undesirable volatiles from the wort.
Logically, if your beer tastes how you want it to taste, it doesn’t matter whether you boil with your lid on, off or somewhere in between but if you are getting certain off-flavours then removing or partly removing the lid may help remove them.
Oh dear yes - realised SMS should have been SMM, and I didn't even get into the LMB 1 and LMB 2 precursors of DMS. I'm clearly in need of proofreading before posting!
Anna
After reading all this...
IGFALD...
IGFALD...
An interesting article that introduces taste thresholds and loss of other aroma chemicals into the argument. The paper though does incorrectly state that the DMS is easily boiled off rapidly which while strictly correct it ignores the constant production of it from precursors and while the wort is hot which goes some way to explain the findings of higher DMS in the beer than in the hot wort. What hasn't been measured in their data is the DMS in the cooled wort.
One of the things I found really interesting about this is the influence of a warm hop stand which would increase the DMS.
Anna
And there was me thinking that by boiling for an hour with the lid off I was just reducing the wort volume, concentrating the sugar solution and increasing the OG by a few points! 
Cheshire Cat
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