Boil time and attenuation

I have always done 60min boils and my calculation of attenuation has been very accurate. My last boil was 30min only, to increase chill haze in the beer.
The attenuation of this batch was much higher, making me think it is related to the short boil driving to a more fermentable wort.
Is there any study on this regard?
I'm planning to brew a 5 gal test batch, boil for 30min and take out two 1gal samples, boil further 30min and take another two 1 gal samples, boil further 30min and take 1 gal sample. Will end up with 5 1gal samples (2-30min, 2-60min and 1-90min) which will ferment independently, same yeast, same temp, and see how attenuation is affected by the boil time.
Thoughts?

Sugar is sugar; it doesn't evaporate. The yeast don't care how long it has been boiled, as long as it's there.

Apparent attenuation can be affected by a number of variables and processes. It isn't only about the average range of attenuation quoted for that particular yeast strain.

bobbrews said:

Sugar is sugar; it doesn't evaporate. The yeast don't care how long it has been boiled, as long as it's there.

Apparent attenuation can be affected by a number of variables and processes. It isn't only about the average range of attenuation quoted for that particular yeast strain.

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my understanding is that the longer the boil, the more caramelization of sugars, which makes it less fermentable. Longer boils also turns the beer darker for the same reason, caramelization of sugars. Perhaps caramelization is not a big issue when the boil is driven by steam, not the case with homebrewers though.

Sounds interesting, look forward to reading about the results. I do have a question though. Are you going to be starting off with more than five gallons to account for boil off? I'd imagine you'd have to or by sample #5 there will be much less than a gallon left.

Dan said:

Sounds interesting, look forward to reading about the results. I do have a question though. Are you going to be starting off with more than five gallons to account for boil off? I'd imagine you'd have to or by sample #5 there will be much less than a gallon left.

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Yes, I plan to start with 6.5gals. The samples don't need to have same starting gravity though, attenuation will be the variable in check.

nilo said:

my understanding is that the longer the boil, the more caramelization of sugars, which makes it less fermentable. Longer boils also turns the beer darker for the same reason, caramelization of sugars. Perhaps caramelization is not a big issue when the boil is driven by steam, not the case with homebrewers though.

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There were probably subtle alterations in the recipe, ingredients, processes of the compared brews, which had an affect on the attenuation. Age/health of the yeast, using a different yeast than before, a mistake with your numbers, etc.

Plenty of brewers employ 60-90-120 minute boils and have no issues with attenuation by reaching 1.011 FG or lower. An extra 30 minutes shaved off the boil is not going to be the one strong variable that magically bring you down to say 1.005 FG

60 minute boils help to promote the formation of melanoidins and caramelizes some of the wort sugars, but that does not necessarily mean those caramelized base malt sugars are ignored by the yeast. Using high proportions of already specialty malts like crystal/chocolate/etc. will have an effect on fermentability, but it isn't the 60 min boil that causes those decreases in fermentability; rather it is larger proportion of specialty grains used in the recipe.

Mash temperature/time is a much more reliable indicator for ensuring a specific amount of wort fermentability than boil length. 60 minute boils also help to evaporate water vapor, condensing the wort to the proper volume and gravity. For the two beers you tested at different boil lengths, were both original gravities identical?

I have brewed over 90 batches of different styles, OG's, mashing temps, grain bills. My FG calculator takes into account all these variables and in the great majority of the cases it predicted FG with a marging of few points. I just found interesting that the first time I boiled only 30min gave me an attenuation much higher than predicted. It could be, like you said, just a coincidence, something else happened.

That's a very interesting observation Nilo. Now I'm curious to go back through my notes and see if i have that kind of correlation. Mash temperature always looked like the big driver for me, but i wonder if i put boil time in the equation if that could explain the discrepancy from predicted to actual.

this is how I predict final gravity:
http://woodlandbrew.blogspot.com/2012/12/final-gravity-in-recipe-formulation.html

WoodlandBrew said:

That's a very interesting observation Nilo. Now I'm curious to go back through my notes and see if i have that kind of correlation. Mash temperature always looked like the big driver for me, but i wonder if i put boil time in the equation if that could explain the discrepancy from predicted to actual.

this is how I predict final gravity:
http://woodlandbrew.blogspot.com/2012/12/final-gravity-in-recipe-formulation.html

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Interesting, your correction for mash temp is similar to what I do, I just give it more weight close to 150 and less at higher temps. One thing though, for the yeast strains that I have investigated, the range of attenuation from the manufactor was so off that I just don't use it at all.
Also, very important to estimate the fermentability of the grain bill as best as possible. Here's what I have setup on my tool based on my own tests/conclusions. Some data can be found HERE for an anlysis on crystal malts.

nilo said:

Yes, I plan to start with 6.5gals. The samples don't need to have same starting gravity though, attenuation will be the variable in check.

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If you don't start with the same gravity, you really need to be able to measure real attenuation rather than apparent attenuation.

I suspect you will not find anything definitive. But it will be interesting to see what you get.