Boil time and boil-off rate

[Gavin C]

Probably a stupid question but after reading the article about extending the boil time to 90 mins for most brews ( currently do 60 minutes for non-Pilsner grain bills) I had a thought.

Would a 90 minute boil resulting in a boil-off of 1.5 gallons be equal to a 60 minute boil off resulting in 1.5 gallons of boil off on different equipment setups. Specifically with regard to driving off DMS and other unwanted volatiles.

I boil off 1.25g/hour in my setup

Is it the boil time that is the key number or is it partly related to boil-off volume.

Any insight or links to explanations would be great

Thanks

 

[MrHadack]

It's actually a very interesting question. Let's think about it:

Many things contribute to the evaporation of water: humidity and atmospheric pressure for starters. Did you know you can make a glass of water boil at room temperature if you were to place it in a vacuum chamber?

So water may be evaporating at different rates depending on different factors. The question is, do those same factors affect the evaporation of DMS precursors in a directly proportional manner, or is DMS strictly a function of heat and time? This is what I found:

"The half-life for DMS is 40 minutes, so half of the DMS will be boiled off in a 40 minute vigorous boil. So if we do the math, a 60 minute boil gets rid of 64.7% of the DMS and a 90 minute boil rids us of 79% of the DMS. That is why most experienced brewers recommend a 90 minute or longer vigorous boil." (Taken from here.)

My guess (and without finding further evidence, it is only speculation) is I think the DMS breakdown and expulsion from the wort is assisted by boiling, but is also an independent function of temperature and time. In other words, heat and time break it down, boiling carries it off.

So the chemical reaction taking place at certain temperatures and time matter. Think of it this way: if you placed a kettle of wort in a vacuum chamber it would start to boil at room temperature, and not 212F. Now let's pretend you added 2oz of 10% AA hops to that boil and let it go for 90 minutes. What IBU would result? The answer is 0, or very close to it. Because the isomerization of hop acids only takes place if the temperature is above 175F... not just because it's being boiled.

 

[JayUnt]

Very interesting and great explanation!

 

[olotti]

There's boil off volume with everyone's system is different and rate of boil off. I just think it takes a couple batches to figure out your system and like me here in mich it's cold and dry so I boil off more now then I would in sept so I use beersmith and have a cold weather setting for my beers I brew now. There's also shrinkage when cooling that I never really looked at but I've now realized I lose .5 gal when cooling too so take that into account.

Also looking at your question Dms is boiled off when u have a 60 min boil it's the temp and time from what little I know that drives it off so if u do a 90 min boil it also can increase concentration of wort and give u clearer beer from what I'm told maybe that's wrong but what I've been told.

 

[Ozarks Mountain Brewery]

also the wider the kettle the more you boil off making more surface to evaporate

 

[Gavin C]

It's actually a very interesting question. Let's think about it:

Many things contribute to the evaporation of water: humidity and atmospheric pressure for starters. Did you know you can make a glass of water boil at room temperature if you were to place it in a vacuum chamber?

So water may be evaporating at different rates depending on different factors. The question is, do those same factors affect the evaporation of DMS precursors in a directly proportional manner, or is DMS strictly a function of heat and time? This is what I found:

"The half-life for DMS is 40 minutes, so half of the DMS will be boiled off in a 40 minute vigorous boil. So if we do the math, a 60 minute boil gets rid of 64.7% of the DMS and a 90 minute boil rids us of 79% of the DMS. That is why most experienced brewers recommend a 90 minute or longer vigorous boil." (Taken from here.)

My guess (and without finding further evidence, it is only speculation) is I think the DMS breakdown and expulsion from the wort is assisted by boiling, but is also an independent function of temperature and time. In other words, heat and time break it down, boiling carries it off.

So the chemical reaction taking place at certain temperatures and time matter. Think of it this way: if you placed a kettle of wort in a vacuum chamber it would start to boil at room temperature, and not 212F. Now let's pretend you added 2oz of 10% AA hops to that boil and let it go for 90 minutes. What IBU would result? The answer is 0, or very close to it. Because the isomerization of hop acids only takes place if the temperature is above 175F... not just because it's being boiled.

Thank you for the well thought out and extremely clear and succinct answer to my question. I really appreciate it. It makes perfect sense.