The higher the gravity of your boil, the lower your hop extraction. Boiling a smaller portion of the wort, means that you end up getting less hop bittering than a higher-volume boil. If you are brewing your beer from a kit, a good kit designer (recipe maker) takes this into consideration and increases the hops to make up for this. So, if your kit called for an exact volume of 2.5 gallons, you will end up with a slightly higher bittering in your brew.
It would seem to me that the lupulin resins would pretty much dissolve in a boiling liquid.. I can't fathom a wort being so dense as to prevent the dissolving.. besides higher the temperature, the easier it is to dissolve something..
and
Actually, your beer will be less watered-down from boiling a higher volume. You should boil the absolute largest volume of beer that your brew kettle and heat source can handle. This is good brewing practice. It conditions more of your water, and produces a fuller-bodied beer.
ok, with my limited knowledge, I should have the same density regardless if I start with 3 gals or 5 gals, if at the end I add water to end up with the same amount of gals in the end..
Beer contains just a small amount of vitamins - that's why it's necessary to drink lot of it
The higher the gravity of your boil, the lower your hop extraction. Boiling a smaller portion of the wort, means that you end up getting less hop bittering than a higher-volume boil. If you are brewing your beer from a kit, a good kit designer (recipe maker) takes this into consideration and increases the hops to make up for this. So, if your kit called for an exact volume of 2.5 gallons, you will end up with a slightly higher bittering in your brew.
Yes, this is true. If you do a concentrated boil with the intention of reducing post boil, you do need to increase your hop additions due to decreased extraction due to increased gravity.
Actually, your beer will be less watered-down from boiling a higher volume. You should boil the absolute largest volume of beer that your brew kettle and heat source can handle. This is good brewing practice. It conditions more of your water, and produces a fuller-bodied beer.
I can agree with this statement too. Plain and simple, it's just better to do a full boil. Not that you can't brew a beer using partial boils and diluting it's just that a full boil much easier to calculate and controll. IMHO it makes a better beer. Perhaps someone else can elaborate on the science behind this.
Scott Townson
May judges be smitten with our brews and long for our nectars throughout eternity!!
Gravity of the Boil
The recipe volume is 5 gallons. The gravity is figured by examining the amount and concentration of malt being used. As noted in the previous chapter, dry malt extract typically yields about 40 pts/lb./gal. Since this recipe calls for 6 lbs. of extract to be used in 5 gallons, the calculated OG = 6 x 40 / 5 = 48 or 1.048
But, since we are only boiling 3 of the 5 gallons due to of the size of the pot, we need to take into account the higher gravity of the boil. The boil gravity becomes 6 x 40 / 3 = 80 or 1.080
It is the gravity of the boil (1.080) that is used in figuring the Utilization. As you will see in the next section, hop utilization decreases with increasing wort gravity. The higher concentration of sugars makes it more difficult for the isomerized alpha acids to dissolve. I use the initial boil gravity in my utilization calculation; others have suggested that the average boil gravity should be used. (The average being a function of how much volume will be boiled away during the boiling time.) This gets rather complicated with multiple additions, so I just use the initial boil gravity to be conservative. The difference is small—overestimating the total bitterness by 1-3 IBUs.
Utilization
The utilization is the most important factor. This number describes the efficiency of the isomerization of the alpha acids as a function of time. This is where a lot of experimentation is being conducted to get a better idea of how much of the hops are actually being isomerized during the boil. The utilization numbers that Tinseth published are shown in Table 7. To find the utilizations for boil gravities in-between the values given, simply interpolate the value based on the numbers for the bounding gravities at the given time.
For example, to calculate the utilization for a boil gravity of 1.057 at 30 minutes, look at the utilization values for 1.050 and 1.060. These are .177 and .162, respectively. There is a difference of 15 between the two, and 7/10ths of the difference is about 11, so the adjusted utilization for 1.057 would be .177 - .011 = 0.166.
The Utilizations for 60 minutes and 15 minutes at a Boil Gravity of 1.080 are 0.176 and .087, respectively. Inserting these values into the IBU equations gives:
IBU(60) = 9.6 x .176 x 75 / 5 = 25 (rounded to nearest whole number) and
IBU(15) = 4.6 x .087 x 75 / 5 = 6
Giving a grand total of 31 IBUs.
Utilization numbers are really an approximation. Each brew is unique; the variables for individual conditions, i.e. vigor of the boil, wort chemistry, or for losses during fermentation, are just too hard to get a handle on from the meager amount of published data available. Then why do we bother, you ask? Because if we are all working from the same model and using roughly the same numbers, then we will all be in the same ballpark and can compare our beers without too much error. Plus, when the actual IBUs are measured in the lab, these models are shown to be pretty close.
Scott Townson
May judges be smitten with our brews and long for our nectars throughout eternity!!
Scott, that all sounds reasonable, but I just find it hard to believe that with a boiling liquid that it would be hard to absorb several micro-millegrams of resin..
Beer contains just a small amount of vitamins - that's why it's necessary to drink lot of it
So, now to convince yourself or prove/disprove it you can do a test.
Make two batches of beer. For one batch do a full boil. For the other batch boil half the amount needed and add water after the boil to get down to the same gravity as the first batch. Use the exact same hops and hop additions for both batches. Boil them for the same amount of time. Use the same yeast.
After fermentation and conditioning do a side by side taste test. If the experts are correct, the full boil batch will have more bitterness than the other batch.
