BIAB pre boil gravity NQR

[NigelP]

Hi,

I have done about 10 BIAB this year and am really enjoying the hobby.

I seem to always get 65 to 66% brew house efficiency. That hasn’t budged since my first brew in the crown urn. This has allowed me to brew consistently and hit my targets, but something doesn’t seem right.

I took some more readings last night and hope someone can enlighten me.

I use a 30L crown urn that gives a boil off of 3 litres per hour. It has 3 litres of dead space.

My brewers friend recipe suggests that from my 3.3 kg of grain I should have got an OG of 1051 with my volumes and 1 hour boil.

I hit those numbers spot on and things went well.

However, the recipe also states that I should have had a pre boil gravity of 1037. This is where things go astray.

After my mash out I measured 1039 after temp correction. The volume was a bit high so I boiled longer before my first hop addition. When the volume was right I measured again and got 1042 after temp correction.

What I don’t get is how my pre boil can be 5 points higher than expected yet I hit my expected post boil OG with the expected volume.

Seems to me that my mashing is yielding a higher conversion than my final numbers would show and that something goes wrong at the boil.

Funnily enough when I put my numbers into brewersfriend dilution calculator it says to go from 19.2 litres of wort @ 1037 to 1051 I would need to boil off 5.27 litres. The recipe calc from the same website with my equipment profile suggests I can go from 1037 to 1051 in hour and finish with 16 litres. This never happens for me.

I don’t know what to tweak. My method, my recipe, my recipe tool, etc.

I am inclined to ignore the water measurements the recipe gives me and run things back through the seperate dilution calculator and work it out myself.

Any advice would be great.

Thanks

 

[NigelP]

So I think I have it figured out now.

Changing the target from 13 litres into the fermenter to 16 litres end kettle volume has made my numbers make more sense.

Plugging in my recorded OG of 1051 now shows an efficiency of 80% post boil.

The pre boil estimate it gives now also matches my recorded 1042. This has never matched up for me before.

This has filled in the blanks for me and gives me more confidence in designing recipes.

Funny how many posts I read before putting this one up.....anyway...

 

[laxation]

what did you change? i think i have a similar problem but confused what you did in the end

 

[NigelP]

Lax, I changed the batch size target setting from Fermenter to Kettle.
It was 13L in the Fermentor and I changed it to 16L in the Kettle.
16L is what I ended up with in my Kettle from my 19.2 L boil volume. 3L of this is trub in the dead space, hence why I had 13L set for Fermenter target volume.

When I changed this to Kettle the estimated original gravity of the recipe dropped way down.
As I recorded an OG of 1051 on my brew day I kept increasing the efficiency setting until the OG matched what I had recorded.
That efficiency is 80%.

I then checked that the water requirements still made sense and also found that the pre-boil gravity estimated matched my measured value too.

I still don't understand why 13L in the fermenter and 16L in the Kettle make such a big difference to the numbers as my equipment profile has dead space set at 3L and boil off at 3L/Hour. It's like the dead space isn't calculated correctly when set to Fermenter. I expected that all this would be taken into account by the formulas for the different targets. Their must be something more to it that I don't fully understand.

I will test this out on my next brew and hopefully everything matches up.