I know that a longer boil will give me a more potent wort and slightly raise my OG, but I was wondering if a longer boil also impacts the fermentability of my wort? I am wanting to use a 2 hour boil on a big SMaSH beer to give some more depth of character, but do not want it to finish high and be cloyingly sweet. Any input or experience here?
I do not believe so…I think the fermentability is determined by the mash temp and duration…Having a mash with beta amylase being the most active with result in higher fermentability…A longer boil will just raise the OG…Im pretty sure
boiling longer is recommended on some beers to develop ‘depth of character’ - doppelbocks, barleywines and scotch ales are some that come to mind. the thought is a more caramelly or melanoid-y character is developed (although there is the argument that neither of those reactions actually occur since caramelization occurs in the absence of water).
anyhow - I don’t know that 2 hours is going to really be noticeable to be honest. most of the aforementioned styles, if the recipe calls for long boil times, are usually in the 3-4+ hour range.
for me personally, I spend 6-7 hours on a brew day as it is, and my standard 90 min boil has always been enough for me. Adding 2 more hours to that better be noticeably better, which longer boils and decoctions have not proven themselves to be.
there is a speed method that is utilized in the famous ‘skotrat’s traquair house’ recipe - you boil down the first gallon of first runnings to a quart and add that to the main boil - this definitely gives you some interesting flavor, and doesn’t add much time. just make sure you watch that small boil carefully…
it won’t affect your fermentability but it will affect your FG because what unfermentable sugars are there will be concentrated along with everything else. the mash, grist, etc. will set the likely Attenuation percentage and this percentage won’t change due to a longer boil (it’ll be 77% for example whether you start at 1.050 or you boil down to 1.075 but the 1.075 is going to have 50% more unfermentables so the FG might be 50% higher (1.018 instead of 1.012). Although I doubt it would be that significant or linear.
this is where I would go with it to deepen the character. or just lot’s more malt. a Single malt beer can be very complex if it’s north of 1.100
Is there an equation to figure how much of a higher gravity to expect over a longer boil? I’m doing a Barleywine with 100% ESB Malt and I do not see that BeerSmith really helps calculating the OG over a long boil time. Also, planning to mash low around 148-150? Shooting for 1.110-1.112 and possibly 1.020-1.022 FG.
You are correct that the boil length will have no impact, but the main driver of fermentability is the recipe. However, given the same recipe, mash temp and duration will have an impact.
This is actually very simple to figure out. Changes in gravity and volume are inversely proportional, i.e., as volume goes down, gravity must always go up, as the dissolved solids don’t go away during the boil but are preserved. It’s a simple scientific and mathematical law. So:
GravityA x VolumeA = GravityB x VolumeB
For this equation, you can dump the 1.0 from the specific gravity and just use the last couple of digits which are also known as “gravity units”. For example, for 6 gallons of wort at 1.040, if you boil down to 4 gallons, you’ll end up with a wort at 1.060, because 6 x 40 = 4 x 60.
Simple as that, really. So, if you know what you want for GravityB and the only unknown is VolumeB, you can rearrange the above equation to look like:
VolumeB = (GravityA x VolumeA) / GravityB
So, for example, if you have that same 6 gallons at 1.040 but you want to get it down to 1.110, then you can figure out exactly how far to boil to get there by doing this math:
VolumeB = (40 x 6) / 110 = 240/110 = 2.18
So, you need to boil off 6 - 2.18 = 3.82 gallons of the water.
Boiloff rates for most people are somewhere around 1 gallon per hour. So, for this example, this might take around 3.8 hours to get down that low. If your GravityA is a lot higher then obviously you won’t need to boil for as long.
