Don't Boil Your Wort With The Lid On!

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a1149913

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So found this on the interwebs, worth the read!

A pretty corny post.
by BeerSensor| Leave a comment
One of the most ubuiquitous flavors in beer, present to some degree in pretty much every beer, is dimethyl sulfide, or DMS. It’s a normal part of beer flavor but, as usual, its acceptability is dependent on the intentions and desires of the brewer. It can be a large portion of the flavor profile of certain beers, while in other beers it is expected to be at much lower levels. For example, Rolling Rock is considered to be a prominent example of a beer which is high in DMS (although in the past it may have been swamped by skunky/lightstruck flavors as I believe Rolling Rock has not always been brewed with light-stable hop extracts).

DMS has the aroma of canned vegetables, particularly corn or creamed corn. It’s a small and simple molecule; as the name conveniently implies, it has two methyl-groups flanking a sulfur atom:

414px-Dimethyl_sulfide_structure.svg.png


Typical flavor threshold for DMS in beer is about 35ppb, and beers from around the world can contain anywhere from 10-200ppb. Typically lagers tend to have a bit more DMS than ales do, but what dictates the DMS levels in your beer more than the yeast is the production parameters in your brewery, particularly the kettle boil and wort-chilling.

DMS is considered to originate from malt, although it is actually formed in the brew kettle. All malt contains a variant of the amino acid methionine called S-methyl methionine (SMM), and it is an intermediate in a number of biosynthetic pathways which plants use to make other compounds. SMM is pulled into the wort during mashing and lautering and as the wort is heated the SMM degrades and is converted into DMS. While the wort is boiled, however, the volatility of DMS allows it to be removed from the wort and out the ventilation stack to never return. If there is no way for steam condensate to escape from your kettle (like if your homebrew pot is covered during the boil) then that condensate will drip back into the wort returning that DMS back into your beer. In such a case, the SMM is still creating DMS because the wort is hot, but the DMS can’t go anywhere so it just continues to build up into higher and higher levels. For this reason, the whirlpool and/or wort-chilling stage after the boil is a critical time in DMS control: if the wort sits too hot for too long, DMS will continue to develop since there is no boil to drive off the compound. I recall some power outages here at the brewery which knocked out the brewhouse for a bit. The brew that was in the whirlpool at the time wound up staying in there for much longer than it should have, which lead to a beer with astronomical DMS levels. At first glance, you may think that controlling DMS might be as easy as making your boils longer to convert all the SMM to DMS and drive it out the stack, but there is enough SMM in most malts that this is not a practical solution: the boil times required to convert it all and volatilize it could be hours long and would be quite detrimental to other wort parameters and the quality of the beer. Some kettles are more efficient at stripping DMS than others, as well. A simple direct fire or steam-jacketed kettle would be less efficient at removing DMS than a kettle with a calandria, which would be less efficient than a Merlin kettle. In fact, I recall brewery which, after installing a Merlin-style kettle, wound up being so efficient at stripping volatiles from the wort that they had to “de-tune” the kettle to make it less efficient since it was throwing off the flavor profile of their beers.

Even after the wort is chilled to the point where SMM is no longer being converted into DMS, the whole corny story isn’t over yet. During fermentation, the carbon dioxide that is produced by the yeast has a scrubbing effect on the DMS, carrying some of it out of the beer. This happens more efficiently at higher temperatures since the fermentations are more vigorous, and for this reason ale fermentations are better at this than lagers. This is why many lagers tend to have somewhat higher levels of DMS than ales do.

Here is a pretty handy chart I found on the internets showing some data about the DMS levels in wort/beer over the course of production. You can see how the levels drop significantly during boiling, but how they can potentially rise again before the wort is chilled. Then they fall again during fermentation as the yeast help blow off some more of the remaining DMS.

dms.gif


Finally, another potential source of DMS can actually come from bacterial infection. Some species of Enterobacter can produce DMS, along with diacetyl. This is quite uncommon in normal production scenarios, but it could conceivably happen more frequently in homebrewing situations. However, the vast majority of DMS in beer comes from the malt and the boil, so if you have an issue with corny beer, check the brewhouse parameters first.

But the story of corny beer doesn’t stop there, no! A challenger appears!

As I collected various flavor compounds that I understood were in beer, I came across a reference to another malt-based compound which was described as “biscuity/malty”. I thought this might have something to do with the biscuity aroma which is a dominant malt flavor in beers which use Victory or “biscuit malt”. Well, I was wrong. As I opened the package of 2-acetylpyridine which Sigma-Aldrich had shipped to me, I realized “This isn’t biscuity at all. This smells like freshly cooked corn tortillas!” It was like opening up that container of steaming tortillas at a Mexican restaurant, or a bag of high quality corn chips. So that’s what my panel calls 2-acetylpyridine now, “corn chips” rather than “biscuity”. Wikipedia says that 2-ap has an odor threshold of about 60 parts-per-trillion, but other literature values I’ve seen indicate that in beer it is closer to 40 ppb (and my experience with it shows this to be pretty close).

2-acetylpyridine, as seen below, is found in malt (and corn chips) and is created by the Maillard browning reactions. These reactions take place when certain types of sugars are heated in the presence of amino acids. It’s a highly complex series of reactions that take place which lead to a whole slew of compounds, including flavor compounds and color compounds. It’s not caramelization, but it can be confused with it if you are unfamiliar with the differences. The browning of the bread as it toasts, the malting of barley, the browning of beef as it cooks – these are examples of Maillard browning reactions.

I’m not going to go much into 2-ap, but just brought it up to show that not all corn-type flavors in beer come from DMS. In fact, I’m starting to think that some of the flavors in our beer that I have previously associated with low levels of DMS might actually wind up being 2-ap and that’s pretty interesting.

108282.jpg


Hope to post again soon! But probably not.
 
Oh.....

Well that scuttles the plans I had for a 'Pressure cooker ale'.
 
Thanks JT. Good post imo.

What I like is that it takes a motherhood statement like 'don't boil with the lid on' and underpins with the chemical reality that's actually going on down there in the hot seething wort. But I think you'll find that some people get flashbacks to past (failed) science exams at first glimpse of a chemical symbol. I replied to thread with this diagram recently and brought the thread to a stunned and silent halt.

Condensation___Hydrolysis.jpg

Let's see if it works again. :)
 
At what point does it go without saying. I haven't read anywhere not to boil with the lid on (apart from where i got this from obviously!). Out of all the important things in brewing, this would be one of the least talked about but one of the most important.
 
While a lot of AG brewers know that lids should be off during the boil, this kind of post helps new brewers, not only by re-iterating something noteworthy but by offering a decent explanation as to why lid off is a good rule of thumb.

Good Post JT.
 
so true jacob. since I started boils I have known not to boil with the lid on. whether extract or AG
 
At what point does it go without saying. I haven't read anywhere not to boil with the lid on. Out of all the important things in brewing, this would be the least talked about but one of the most important.


Jacob, nice article, but brewing without the lid on is not the least talked about subject by a long chalk. It's talked about in just about every text on boiling wort.

cheers Ross
 
Good info, i am guilty of boiling with the kettle lid on as i did not know about DMS. Good idea to keep the lid off from now. :icon_cheers:
 
At what point does it go without saying. I haven't read anywhere not to boil with the lid on (apart from where i got this from obviously!). Out of all the important things in brewing, this would be one of the least talked about but one of the most important.
Palmers book "how to make beer" explains this theory as well
 
Is that similar to his other more well known book "How To Brew"?

I found out not to boil with the lid on when my first two all grain efforts tasted like corn.
So similar it's the same, blame my typo on the three pints I had of ipa. Having these kegs full is killing me!
 
I think its generally assumed that all AG brewers have read palmers book, because if you haven't read it you definitely should. ;)
 
I boil with the lid off but I bring it UP to boil with the lid on.. Is this also a bad option?
 
That's fine as long as the boil is full enough and long enough. I do the same.
 
I agree, I bring up to the boil with the lid on & remove once it starts rolling. I do take the lid of a few times & shake off the condensation it makes on the lid though.
 
As I opened the package of 2-acetylpyridine which Sigma-Aldrich had shipped to me

Good article.

But, this dude goes trawling through the sigma catalogue
41pCHaLo9HL._SL160_.jpg
which is a brick.. to order different chemicals identified in brewing processes from mass spectometry, to test them by aroma from bottles of ultra-purified solid powder?

I guess I have to take my hat off to him, but the shit has a flashpoint of 73C and while they're usually a bit over-the-top, the msds for it states to use a full face respirator when working with it. If it is present as trace elements in wort, I dont really understand what he has to gain by smelling a potentially harmful ultra-purified version of it, particularly when it is present as a different form, with potentially different vapour products than that when it is present as a soluble form in wort. Also, the concentration as a vapour would be much higher.. and while chemists don't understand the biology of smell, as a biologist, I know that varying concentrations of particular substances can illicit slightly different notes. So I don't know how scientific his testing is, unless he dilutes it down to 40 or 30 parts per billion as a solution, and *blind* tests that..

Pretending that his findings were properly controlled, and found to be true, then how does he determine that one stops Maillard Reactions occuring during a wort boil? It is pretty frickin hard! What is the volitility of 2AP? Does 2AP serve any other purposes during the boil, does it assist with hop isomerisation? does it accelerate other processes? would a reduction in 2AP negatively impact other characteristics of flavour, or its fermentability?
the list goes on..

I like that he's tinkering here, but he needs to be more methodical about his approach and cover his arse more, not to mention, not kill himself when sniffing bottles of ultra purified materials.
 
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