Calculating Og

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Here's the method for calculating OG for those that have asked for it.

I'll give some theory first as it good to know.
anyway fermentables are given as a % of 386.
which is the gravity of 1 kg of cane sugar in 1 litre of water ie 1.386.
Sugar being the most fermentable everything else is given as a percentage of that with pale malt around 81% ie 386*.81 = 312.
this number is refered to as the extract potential and ussually you'll see it with HWE after it which stands for Hot Water Extract this is the gravity of 1kg of that fermentable in 1 litre of water.

anyway you don't need to understand all off this to do your calculations as i'll give you a table as a guide for each fermentable.

The calculation you'll need to use is this.
(Fermentables in KG * HWE) /Volume in litres.

The calculation in practice for a 23litre brew with 5 kg of pale malt looks like this.
(5*312)/23= 67 so your og potential is 1.067.
for a mash brew like this you then times this again by your effiency for your system which is ussually around 70% so 67*.7= 46.9 so your expected OG is 1.046.

For a extract brew you don't need to worry about effiency as you will always get 100% of the extract potential.
Here's a 23 litre extract brew using 3 kg of dry malt extract (DME being 384HWE or there abouts)
3*384/23=50 (1.050)

and for a 3.5 kg 23litre LME brew it would look like this with LME being around 308.
3.5 *308/23= 46 (1.046).

if your using both DME and LME then you basiclly do two calcultions one for each then add them together same as if your adding a mash you'll do another calcultion and add that on aswell.
say you use 1kg of DME and 1kg of LME nd one KG of pale malt is would look like this.
((1*384)+(1*308)+(1*312))/23 = 43 (o.g 1.043)
but for the 1 kg of pale malt you'll have to factor in your effiency.

Here's a table of common fermentables.

Pale malt,pilsner and munich malts = 317
crystal malts will all vary but around 275-300
carapils = 309
roasted malts and roast barley = 275
dried malt extract = 384
liquid malt extract =309-317
sugar = 386

Hope that helps those interested in finding out the manual calculations.

If you don't know you effiency take the OG you got from your mash and divid that by your total extract potential you calculated.
ie say your potentail was 1.067 and you got 1.047 then 47/67 = .7 so your effiency was 70%.

Cheers Jayse


Good stuff, Jayse!

For those using kits, a 1.7K kit will add 23 points to a 22L batch

Jovial Monk

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