Here is how it might go:
Mash in 53L.
12L sparge. He has 11Kg of grain so you would expect about 11L loss to grain (absorbed by the grain).
Now we have 54L pre boil.
We might lose 10% to the 60 minute boil (54L -5.4L).
Now we have 48.6L post boil.
We might even lose 4% to cooling (the cool wort takes up less space than the hot wort. 48.6L - 1.94L).
Now we have 46.66L of cooled wort. How much are we going to lose to kettle trub before it goes to the fermenter? Let's say about 2L.
Now we have 44.66L of wort into the fermenter, not 53L. If he got 43L into the fermenter, I'd find that plausible. To get 53L volume he would need an additional sparge of 8.34 L for a total sparge of 20.34L.
The malt pipe will hold quite a lot of sugars amongst the grist. My understanding of astringent tannins being extracted from sparging has more to do with the temp of the sparge water (i.e. too hot) and the gravity at which the sparge comes out. IIRC Isn't it thought to be about 1.010 SG where tannin extraction from the grain husks might occur most rapidly? I have sparged my 50L malt pipe with about 20L in total and the last runnings were still around 1.020 SG. Caveat being that I quite often extra-sparge over a bucket to collect runnings to top up the boil should I be short on volume near the end of the boil. You could even extra-sparge over a bucket to collect additional wort for yeast starters.
edubrueurope - how do you get losses of only one litre, or did you mean 43L, not 53L into the fermenter?
Thanks for all your comments.... sorry, maybe i didnt give enough info!
Malt - hand milled on a corona set at 1.2mm
53 litres water in
12 litre sparge at 65 deg C
90 min boil
post boil 51 litres
4l losses to trub
47 litres to fermenter at 16 Plato
45 litres bottled at 7 Plato
Where am i going wrong?
PS Like the idea of extra sparge for the yeast starter... will be trying that out on the next brew.