I made some Extract brews with 2kg Pale DME and 1KG Amber DME, so a conversion of that would be appreciated.
In 20 litres that would take you to an original gravity of 1.052 and a colour of about 6ERM/12EBC which equates to pale malt with 2% crystal 60L - say 5kg Otter and 100g crystal 60L.
Can you help me out with amounts for a 20L batch. Please, assume i'm an idiot.
You're not an idiot, you just lack knowledge. And that is fixable, unlike being an idiot.
As others have said, software is a big help when building your own AG recipes - whether it's the paid ones, a free one like
Brewtarget, or a website like
Brewersfriend. But if you're not ready for that, the numbers happen to fall out for a good rule of thumb :
1kg base malt in 20 litres at 70% efficiency -> ~10 gravity points which with a medium-attenuation yeast -> 1% ABV.
So :
5kg base malt in
20 litres at 70% efficiency ->
1.050 original gravity which with eg S-04 yeast ->
5% ABV
In fact with modern malts you tend to get a bit more than that, but it's close enough (or just assume slightly efficiency of say 68% to make the numbers work). Base malts are any malts with a "full" amount of enzymes for breaking starch down into sugar - pale malt, pilsner, even slightly darker ones like Vienna. But the enzymes get killed by the longer cooking needed to make darker malts, and the starch itself becomes less accessible, so assume speciality malts release half as much sugar per kg compared to base malts. So :
Instead of
5kg base ->
1.050, you want
4.9kg base + 0.2kg (4%) crystal -> 1.050 and so on. But 2-4% crystal is a pretty flexible base for most styles.
Brewhouse efficiency is a measure of how much sugar you get out of the grain versus the theoretical maximum. Somewhere around 70-75% is considered typical for BIAB, all-in-one systems like Grainfather get over 80%. I wouldn't sweat efficiency too much - what matters is being able to predict efficiency rather than its absolute number (unless you're brewing for profit), so consistency is more important. If your efficiency is low, all it means is you have to add an extra 50p of malt, which is nothing in the global scheme of things. So 70% efficiency is a reasonable assumption, but your first one or two AG brews will probably end up closer to 60% so it's worth adding an extra 15% or so grain in those early brews - better to go a bit higher than end up with gnat's urine! For the same reason it's no bad idea to have some DME to hand if it needs a bit of a boost.
Attenuation is a measure of how well a yeast converts a sugar solution into alcohol. Typically you end up with final gravity (FG) at about a quarter of the original gravity (OG), implying an attenuation of 75% - formally, apparent attenuation = 1 - (FG/OG)
or = (OG – FG)/OG.
So a 75% yeast will take 1.050 wort to 1.0125 (just divide 50 by 4) and ends up at about 5%. So at 75% attenutation it's roughly 10 points of gravity ->1% ABV, and it changes by about 0.2% ABV for every 3% attenuation up or down. So you might get 68% attenuation from a yeast like Windsor, which would end up below 4.6% but with more body, or 85% with a saison yeast for 5.6% and a drier, thinner beer.
All the above are not completely accurate, but they are close enough to have in your head to be useful reality checks - or when you just need to do a quick brew without getting the computer/phone out.
