The Boil

[GuingesRock]

When I started brewing, I was led to believe that you boiled to get rid of DMS, BUT it’s the high temperatures that create DMS from precursors. So you are boiling for 60 - 90 minutes to get rid of the DMS that is caused by the boiling…basically shooting yourself in the foot, using a lot of energy in the process and creating clouds of steam.

Boiling the wort is a relatively new practice in the history of beer. Some beers are still made today without boiling – eg Berliner Wiesse and they do not have DMS.

I think that boiling is mostly for sanitation. Maybe for isomerization of hop alpha acids too, But I’m interested to know if there are other advantages, and also disadvantages to boiling. There are other ways around sanitation, for example pasteurisation, and the hop issue also.

There were a number of questions on my last site about loss to evaporation during the boil, whether the boiling pot should be tall and thin, or short and wide, should the boil be vigorous, should the lid be partially on, should you float a bowel on the surface etc.

I tried to answer some of the questions using simple physics, and have written something on that below, and posed some more questions of my own (if anyone feels like answering them that would be great). I think it’s important to think about because of energy use and time considerations. The big breweries must have thought these things through as both are expensive commodities.

It would be interesting to make a no-boil beer. Has anyone here done that?

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A larger surface area of the boiling liquid leads to a higher evaporation rate. This is because there are more surface molecules that are able to escape. But other things affect evaporation:

1. Temperature of the liquid, since when hotter, water molecules have higher kinetic energy (they jiggle around more), and can escape more easily from the liquid.

2. Concentration of water vapour in the air above the surface: Putting a lid on a pot of water increases this and the water heats faster because less energy is lost in the evaporation process.

3. Flow rate of air over the surface

4. Atmospheric pressure: the higher the pressure, the less easily water molecules can escape from the water to gaseous form.

All of these things are fine when the water is heating up, and they all apply, but once you reach boiling point, and the boil is on, things change.

Once at the boil, the heat that is applied to the bottom of the pot continues at the same rate and is no longer being employed to increase the temperature of the water, since at atmospheric pressure, the water will go no higher than 100C and that energy has to go somewhere. Once the boil has started, all the energy that isn’t lost through the sides of the pot or the surface of the liquid, through convection and radiation, is now employed in evaporation.

Placing a floating bowel on the surface of the boiling wort, may well decrease evaporation. It reduces the area on the surface of the liquid, but that should not make a difference when the water is actually boiling. What a floating bowel will do is dissipate heat to the air above. It will take heat from the liquid and radiate and convect heat away from the boiling liquid, and consequently there will be less heat available to cause evaporation.

I believe that it isn’t the top surface area of the liquid that affects the evaporation loss in the kettle once the wort has reached boiling point, but rather, it is the surface area of the sides of the pot. A tall low diameter pot, has a lot of steel on the sides (in proportion to the volume of liquid in the pot) to dissipate heat, and consequently less heat is employed in evaporation. The liquid in such a pot has a small top surface area and there will be less evaporation while the pot is heating up, and the pot will heat up faster as a result. Once the water has reached its maximum temperature of 100c and can go no higher, then all of the heat energy applied to the pot, that can’t escape from the sides of the pot, will be employed in evaporation. Conversely a shallow, wide diameter pot, will have proportionately less surface area of steel to dissipate heat and more energy will be available for evaporation.

By floating a bowel on the surface of the water, you are in effect adding to sides of the pot and allowing more heat to dissipate through convection and conduction, and thus there will be less heat energy to cause evaporation. The effect of the floating bowel is thus to dissipate more heat, so that less is used in evaporation and less evaporation occurs. But why not simply turn down the heat and save yourself the trouble!

Dimethyl sulphide (CH3) 2S, is a water-insoluble inflammable liquid that boils at 37C. It is highly volatile. Every bubble of steam will carry with it some DMS, and the longer the boil, and the more vigorous the boil, the more DMS will be removed.

I wonder if DMS removal might be proportional to evaporation loss during the boil. If that is true, then a short vigorous boil would achieve the same as a longer slow boil. Thus, the wort should be boiled not according to time or the vigour of the boil (which can’t be measured), but should be boiled at whatever rate, until a certain loss from evaporation has occurred. Eg. boil as fast as you like or as slow as you like, until the wort has decreased in volume by say 10%. If that principal does apply, then using a volume parameter to determine when to finish the boil would help with consistency from batch to batch.

The other side of this issue is DMS production during the boil. If DMS continues to be produced for a period of say 90 minutes, then the boil should be for 90 minutes. I don't know how long it takes for DMS production during the boil to cease.

I’m leaning towards a slow boil for 90 minutes, but it’s only a gut feeling.

What do the brewers on here do in terms of boil vigour and time, and reasons behind what you do?

[mr x]

I boil 90 minutes or less. Target gravity is my rule.

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[LeafMan66_67]

Usually a 60 minute boil for me, while hitting target gravity. I'll do 90 if using Pilsen malt to drive off DMS - only because of what I've read, no science behind it on my part.

[GuingesRock]

Thanks! I'm interested to know what you think the vigour of the boil should be for a 90 and a 60 minute boil also.

Target gravity seems like a good idea. I'd need a refractometer to do that.

[mr x]

Good rolling action without boiling over.

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[GAM]

I do gravities of hot wort by putting it in a SS bottle and bathing that in ice to get to temp and using a hydrometer. I have a refractometer if you want it, then you can tell me how to use it.

Sandy

[LeafMan66_67]

Thanks! I'm interested to know what you think the vigour of the boil should be for a 90 and a 60 minute boil also.

Target gravity seems like a good idea. I'd need a refractometer to do that.

I use a vigorous boil, boil off is approximately 5L per hour.

[GuingesRock]

I do gravities of hot wort by putting it in a SS bottle and bathing that in ice to get to temp and using a hydrometer. I have a refractometer if you want it, then you can tell me how to use it.

Sandy

Thanks Sandy, I was thinking though that to boil to target gravity, I might need to check gravity every 5 minutes or so.

I haven’t used a refractometer before but my wife uses them constantly at work. Maybe she can show us both.


Why the vigorous boil? I can see it for a 1 hour boil, but would I have problems if I did a slow boil for 90 minutes?

[RubberToe]

IIRC vigorous boil also aids in hot break. I guess you wouldn't get any hot break in a no-boil situation either.

[RubberToe]

Also, you need to boil your hops if you want any real IBUs.

[jacinthebox]

I use a 90 min vigorous boil, it was how I learned to brew. Via Brewnosers and the rest of my Internet research.

[dexter]

I was led to believe that a vigorous boil is over kill, as long as its a boil its doing its job. It's not getting hotter than boiling and at that point aren't you just wasting water, fuel ect..?

[sleepyjamie]

Rolling boil here for me especially on lighter beers as what ive read in many of my books Vigorous boils can cause increase srm.

[dexter]

I do gravities of hot wort by putting it in a SS bottle and bathing that in ice to get to temp and using a hydrometer. I have a refractometer if you want it, then you can tell me how to use it.

Sandy

You can order some off eBay that have both brix and specific gravity. So basically like a hydrometer but quicker and easy to use. Get the wort to 20 degrees or lower and read just like you would a hydrometer.

[LeafMan66_67]

Vigorous boil or rolling boil... Who can show me the difference between the two? I said vigorous, but never really had any issues with increased SRM, so perhaps mine is a rolling boil... Pretty subjective if you ask me.

[sleepyjamie]

http://byo.com/recipes-tag/item/249-boi ... ed-brewing" onclick="window.open(this.href);return false;

Good article. Also it appears boiling point changes based on altitude.

[sleepyjamie]

Vigorous boil or rolling boil... Who can show me the difference between the two? I said vigorous, but never really had any issues with increased SRM, so perhaps mine is a rolling boil... Pretty subjective if you ask me.

Good point. It's all subjective and depends on your equipment, methods and results.

I've seen some guys point to the point were it looks like and active volcano and others where it looks like calm waves off the ocean.

[RubberToe]

Or a witches brew...

Sent from the brew timer.

[Stusbrews]

[/quote]

Thanks Sandy, I was thinking though that to boil to target gravity, I might need to check gravity every 5 minutes or so. [/quote]
You dont need to check gravity every 5 min.....that can be calculated from your original reading using gravity units/liter.( 1.056 = 56 units) in 20l, thats 2.8gu/l.(56/20) If you want OG of say 1.050, its 50/2.8 which leaves you with 17.85, your volume at correct OG. Or close enuf.

[GuingesRock]

You dont need to check gravity every 5 min.....that can be calculated from your original reading using gravity units/liter.( 1.056 = 56 units) in 20l, thats 2.8gu/l.(56/20) If you want OG of say 1.050, its 50/2.8 which leaves you with 17.85, your volume at correct OG. Or close enuf.

Interesting! And very useful to know. Sort of back to the volume thing again.

Sounds like I’m going to be ok with a lowish rolling boil for 90 minutes. That’s what I’ve been doing all along, but wasn’t sure I was doing the right thing, and I’d have never known if I hadn’t asked.

Interesting link Sleepyjamie.

Thanks everyone for all the experienced information.

[Stusbrews]

All my brewing has been done on the stove, (no burner) so never have had a really strong boil but they all turned out just fine. Mostly 90min boils for me, with several overnite simmers for smash beers as well. Try doing that with a burner! lol

[LiverDance]

I boil 90 minutes or less. Target gravity is my rule.

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[mr x]

I judge my final desired volume with my target gravity. With my past experience, I know my system will be 90 minutes or under.

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[Tony L]

My system is less science based also. I collect wort and use a steady rolling boil of usually 60 minutes to get my starting gravity. I find using the refractometer to be ideal for my method because it is so quick. I have been doing it this way for so long now I just do it without thinking.

[mr x]

This. Thinking never worked out right for some reason, lolololilololololololololol.

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