So I am brewing my first all grain beer.
It takes a few times of brewing to refine the various sub-processes involved. Reduce losses, improve efficiencies, taylor recipes to
your processes to match the outcome of the final beer you're after.
I used a one pot setup with a fine mesh mash strainer and have a pump for recirculating and cooling via plate chiller.
That's a good start, a variation on BIAB, Mash In A Basket.
A sparge (rinse) will help increase your mash/lauter efficiency, to reclaim much of the high gravity wort trapped in the basket with (wet) grist.
The recipe says I should have gotten a volume of about 21 litres but I ended up with about 18 litres at a gravity of 1.060.
Volume and gravity are related like a
rubber band. Longer but thinner vs. shorter but thicker.
Length = volume
Thickness = gravity
You were a bit short on volume because you sustained a larger total
volume loss than envisioned.
We went over that already how to bring that closer to predictions with your system.
But you also
lost gravity. The sparge after the mash, as I mentioned above, will help you raise your gravity (total points converted/extracted).
Among a good handful of factors, fineness of milling may well be the biggest factor in mash efficiency (gravity points extracted).
The finer the grist is milled, the more thorough and faster the starch conversion, and higher the yield (wort gravity, points).
For that, mill/crush your grain finer, using a
narrower gap, such as 0.025" instead of 0.045" to which many standard grain mills/crushers are set for.
Especially when you're mashing in a mesh bag or basket, you can mill rather fine. The bag or basket is your strainer that separates wort (liquid) from grist (solids).
If there's a large % of "sticky grains" in there (wheat, rye, or oat malt, or any flaked goods), add a few handfuls of rice hulls (or oat hulls) to the mash, to keep the grist lusher.
Reduce the amount of wort left behind (lost) at various stages, such as vessels, apparatus, hoses, etc. Any wort that doesn't make it into your fermentation vessel never becomes beer.