What am I doing wrong, or right?

[marcarm]

Made my 5th BIAB tonight, a recipe from another forum which was meant to produce 23l @ 1.048.

I use the maxi BIAB, basically boil to the top of my boiler then liquor back to my desired og, so I get a variable brew length. I normally rinse the grain a few times and add this to the boiler as/when it can take it.

When I finished tonight, I had 18l from the boiler @ 1.072. Using an online calculator it would have taken 9 litres to get my planned og, so would have ended up with 27l. Now don't get me wrong, I'm not complaining, but I would like to understand why I'm getting extra beer

In the end I couldn't dilute like I wanted as it wouldn't fit in the FV, so went to about 1.056 as I wasn't comfortable with any less head room.

[Bazz]

I'm a complete noob at this, but the only thing that i can think is that you had better efficiency than that which you had in the calculator.

[marcarm]

I thought my efficiency must be good, I followed a recipe so no calculator involved in this one.

This has happened in brews before but never to the extent that I got last night.

[rpt]

You can't assume that you will have the same efficiency as anybody else. I never follow a recipe directly but put the figures into the BIABacus spreadsheet. It then tells me how much grain to actually use. This also allows for the fact that your efficiency will depend on the gravity (higher gravity mashes are less efficient). The default figures from the BIABacus were pretty good but I have tuned it slightly as I always came out with slightly stronger wort than intended.

[RdeV]

Intrinsically MaxiBIAB has potential for excellent efficiency, but perhaps your original recipe factored in an unusually poor efficiency or maybe the quantities of malt or volumes were inaccurate, e.g. a generous supplier gave you a little extra base malt for free. You're not doing anything wrong, but I'd also check all of the volume, mass and specific gravity measurements- while its always pleasing to score a bonus, the last thing a novice brewer needs is confounding results!

Ps. If I find myself with surplus wort, I freeze it for yeast starters.

[Fil]

efficiency and boil off rate are 2 variables particular to each individual brewery, boil with an identical boiler to me for the same period and an identical starting volume, and guaranteed my final volume will be different to yours, how much heat is radiated from the pot will differ depending on location less if insulated more if in a draught or wind out on the patio,,

much the same as your mash.. have you calibrated your thermometer, checking it against close to 0C (ice water) and close to 100C (boiling water/steam) will indicate any error , a slight variance in strike and mash temps will effect the enzyme activity

as you brew your records will indicate both your true brewhouse efficiency and boil off rate which you can then plug back into your recipe to derive the grainbill (base malt) quantity and volumes to use to hit both FG and volume targets.

sounds like your doing great, just up the brewhouse efficiency estimate to match your results and tweek your volumes and you will be hitting both targets with better accuracy