Calculating partial boil recipes and Beersmith

[frankvw]

I'm sure I'm overlooking something obvious, but I just can't see it...

I'm trying to calculate a few recipes for a stove-top partial boil in small pots. Instead of boiling 3kg of malt extract topped up to 15 liters, I want to boil 1kg of malt extract topped up to 5 liters, then add the remaining 2kg of malt extract post-boil and then top up to 15 liters when transferring the wort to the fermenter.

As far as I understand it (please correct me if I'm wrong) my hop utilization should be roughly the same, since the wort gravity is the same. In fact, Palmer & Zainasheff ("Brewing Classic Styles, p.35) state that converting a recipe from full to partial boil amounts to boiling all the hops with half the malt extract in half the water. I'm using a 33% boil volume instead of 50% but as log as the boil gravity is the same (which it is) this should not matter significantly (within reasonable limits, of course).

But when I run this through Beersmith, everything starts to go sideways when I change my equipment volume from a 5 gallon / 19L pot to a 2 gallon / 7.6L pot (using the pre-set equipment profiles). Suddenly my preboil gravity is more than 1.100 and my hop utilization takes a complete nosedive (15 grams of 11%AA bittering hops boiled for 60 mins gives me 4.1 IBU's).

So... What is the proper way to calculate a recipe (OG, IBU's, color etc.) in Beersmith for partial boils? Also, what is the relationship between boil volume and hop utilization (in real life and as far as Beersmith is concerned)?

 

[Oginme]

First, do not rely on the preset equipment profiles. They are intended to give you a starting place to customize your own profile. Switching from one equipment profile to another means that you may also be changing the boil off rate, trub and chiller losses, and top off volumes between the two profiles. This will give you very different results.

Next, I don't know how you are differentiating it in your recipe, but you need to mark the extract as a 'late extract boil addition' so that the program does not count it as a starting addition.

Third, are you using liquid or dry extract? If you are using liquid extract, your addition of 1 kg diluted to around 5 liters of water will give you a gravity of around 1.063. Dry extract will give you a gravity of around 1.070. If your additions are correctly expressed in the program then you should be close to these numbers.

As far as the IBU estimation goes, if you are using the Tinseth formula (default in BeerSmith), then the IBU will be reduced based upon the gravity of the wort. The higher the starting gravity, the less utilization you will realize from your hops. In real life, all the models are based upon one person's testing and observations on their system with their process parameters. The relationship of that model to yours is something you need to figure out through either testing or tasting.

 

[chickypad]

Try checking the "add after boil" box on the extract.

 

[frankvw]

OK, so I'm having a major fight with Beersmith's equipment profiles right now. Let me resolve that first so I know what I'm looking at, and then deal with partial boil conversions.
Thanks for pointing me in the right direction, guys!