4 litre boil for 23 litre batch

[Urideout]

I am hoping I can get some of your thoughts on the consequences of brewing using the following method (not the recipe):

-Steeping some grains i.e 200g Light Crystal for half an hour 65 degrees c in 2 litres of water then straining them with extra 2 litres of water.
-Boiling the (now) 4 litres adding 250 g LDM bring to the boil and add 30 g simcoe boil for 30 mins
-add 15mg cascade (after the 30 min as above) boil further 15 minutes then add 15mg citra for a 10 minute hop stand
-cool wort and add to FV that contains light pale liquid extract (not hopped) and water, add dextrose and water to fill to 23 litres

My questions are not about the hop combinations or Abv or recipe advice. I am keen to know how a small-sized boil can affect the IBU's or any other aspects of the brew. I would like to know why most extract boils and brew methods along these lines are mostly done by boiling 11 litres or more?

Thanks in advance, and I hope my post makes sense.
Cheers

 

[RM-MN]

One reason for the extra amount of wort for the boil is to keep from boiling all the water away. Many people report boiling off 4 liters of water during the boil.

 

[VikeMan]

You are describing an extreme version of a "partial boil."

One disadvantage is that hop utilization (IBUs and hop flavor/aroma) is reduced when the boil happens in a small volume. Another is that maillard reactions, which darken the wort through production of melanoidins., are increased.

It's generally a best practice to boil the full volume. If not possible, boil as much of it as possible.

 

[BrewnWKopperKat]

I would like to know why most extract boils and brew methods along these lines are mostly done by boiling 11 litres or more?

Book/article/recipe authors generally assume the ability to boil at least 3 gal of water (using a stove as a heat source). Partial boil with late additions (of DME/LME & water) is a well known technique for brewing in the kitchen to make 5 gal batches.

cool wort and add to FV that contains light pale liquid extract (not hopped) and water, add dextrose and water to fill to 23 litres

Book/article/recipe authors will boil / pasteurize all the DME/LME in the recipe to eliminate the risk of a spoiled batch due to potential infection / contamination of ingredients.

 

[Urideout]

Thanks very much, everyone for the information! Exactly what I was looking for, very helpful indeed. I have been using this method but with the extract tins that are hopped and I have only been boiling hops for up to about 15 min. Time to get a bigger pot so I can play with the bittering side of things.