"Vigorous" boil?

I feel that over boiled wort tastes "worty". Its kind of a dull, caramel note to me. It can also be a result of under-attenuated beer which is something Im a little picky about. I find drinkability goes up with well attenuated beers, usually 80% or more.

Comment on NB and boiling, IIRC they bought a Steinecker Merlin system back in 2001. I recall this being a big deal at the DrinkTec/Interbrau trade show at the time. Merlins actually boil shorter duration and at lower temps than traditional systems and scrub the wort via an inverted cone in the kettle, the ripples as the wort falls down the cone help to scrub the volatile compounds out and isomerize the hops.

 

GEA (Huppmann) makes reference to gentle boiling and high evaporation rates on their system.
http://www.geabrewery.com/geabrewery/cmsdoc.nsf/WebDoc/webb9dddkg

 

Jim, is the isomerization of hops solely a function of temperature or does physical activity (e.g., vigorous boil) increase the isomerization process as well?

Cheers!

 

My guess is its dependent on hop type - with whole hops benefiting from the movement and flow.

 

Hi Jack,

My old advisor at OSU did a study on this: http://www.ncbi.nlm.nih.gov/pubmed/15913306

 

Can you translate the results?

 

The rate of isomerization of alpha acids to iso-alpha acids (the compounds contributing bitter taste to beer) was determined across a range of temperatures (90-130 degrees C) to characterize the rate at which iso-alpha acids are formed during kettle boiling. Multiple 12 mL stainless steel vessels were utilized to heat samples (alpha acids in a pH 5.2 buffered aqueous solution) at given temperatures, for varying lengths of time. Concentrations of alpha acids and iso-alpha acids were quantified by high-pressure liquid chromatography (HPLC). The isomerization reaction was found to be first order, with reaction rate varying as a function of temperature. Rate constants were experimentally determined to be k1 = (7.9 x 10(11)) e(-11858/T) for the isomerization reaction of alpha acids to iso-alpha acids, and k2 = (4.1 x 10(12)) e(-12994/T) for the subsequent loss of iso-alpha acids to uncharacterized degradation products. Activation energy was experimentally determined to be 98.6 kJ per mole for isomerization, and 108.0 kJ per mole for degradation. Losses of iso-alpha acids to degradation products were pronounced for cases in which boiling was continued beyond two half-lives of alpha-acid concentration.

My translation:
Temperature, not boil vigor appears to be the significant factor (for hop utilization/isomerization) with diminishing returns after boiling for ~ an hour. Don't see anything earth shattering here.

 

Boil "vigor" is sort of an ambiguous term. Water boils at 100C, and you can't raise the temperature above that unless you change the boiling point somehow (a pressure vessel being the most common method). What you can do is add more energy so as to increase the evaporation rate. In other words, a vigorous boil evaporates more water because you're providing more joules per mol, but the temperature is static at a given atmospheric pressure. Since the rate of isomerization depends on the temperature, only the duration of the boil is going to have a significant effect. Note that this also means you could attain a satisfactory isomerization rate at a less-than-boiling temperature, if you so chose. This (a "cold boil") could potentially effect DMS levels and other things down the road, though.

 

Peter, what about the vigor of the boil for clarification:

“The coagulation and precipitation of proteins is a key factor in producing clear, stable beer.”

Cheers!

Jack

 

What about it? There is nothing in your link that says anything about the vigor of the boil affecting coagulation.

 

Thank you!

 

Thank you!

 

Below is what Mr. Wizard wrote in an October 2013 edition of BYO discussing haze in beer.

“A vigorous kettle boil for at least 60 minutes is very important for beer flavor and beer clarity since certain undesirable aromas and protein and tannin fractions are removed during the boil. Many brewers add Irish moss, a good source of kappa-carrageenan, to wort towards the end of the boil in an effort to increase the size of protein flocs. Since the large flocs settle faster than the smaller and more fragile chunks of protein "break," or denatured proteins and protein fragments, Irish moss aids in removing these haze-active proteins from wort and beer. With or without Irish moss, a vigorous boil is a must. Almost all commercial brewers use whirlpool vessels to separate protein break and pelletized hop residues (when pellet hops are used) from wort following the boil. Many homebrewers have begun using whirlpool-type vessels for the same purposes.”

Cheers!

 

Have you ever actually tried a gently rolling boil?

Quotes from a magazine column without any explanation of the science really don't mean a lot, even with underlines and bold fonts added. Actually, the first sentence is a hoot. It could be rewritten this way: "Protein and tannin fractions are removed during the boil. Therefore you must boil vigorously, for at least 60 minutes." Does that sound logical?

 

You can get satisfactory coagulation (hot break) from 20 minutes of normal boiling. You absolutely don't need 60 minutes for that. Longer boils are for:

• extract concentration
  
• color development
• hop acid isomerization
• Undesirable flavor steam distillation (i.e. getting rid of DMS).

You can make an excellent beer with good clarity with a 20 minute boil, if you so chose. Boil "vigor" is really only needed if you're trying to drive off as much water as possible and/or ensure sufficient DMS removal in a short boil.

With respect to homebrewing, I'm actually a fan of gentler boils, as long as I'm otherwise hitting gravity/iso targets. In the big breweries we use a calandria, so it's vigorous whether we like it or not

 

Peter, thank you for your responses.

You made mention of: “In the big breweries we use a calandria, so it's vigorous whether we like it or not.” We homebrewers often try to mimic the brewing practices of commercial brewers with the notion that if the commercial brewers do it then it is an overall brewing best practice. Your scientific input is most appreciated.

Cheers!

Jack

 

This may be true for some homebrewers, but not all. There are lots of things the pros have to do because of limited time or money, or because of the scale of their equipment/batch sizes. Some of it should not be, or doesn't have to be, mimicked.

 

The point has been made that the boil cannot be higher that 100 degrees. But that only applies to the bulk of the liquid and there will be higher local temperatures in the kettle. Close to the element the heat transfer isn't instantaneous and superheated steam is initially generated. This cools off in contact with the bulk liquid but as this too gets towards 100 degrees the cooling takes longer.
Actually 100 degrees is for pure water.solutions have a slightly higher boiling point.

 

One other thought , the 100 degree boiling point applies to standard atmospheric pressure. At the bottom of a copper the head of liquid raises the pressure significantly and the local boiling point is raised.About one degree per foot of wort depth is a rule of thumb figure.

 

One degree C per foot, I'm assuming?