calculating extraction

[Cadbury]

G'day Men,
I am totally confused about extraction/efficiency. I have read John Palmer's book and he mentions measuring the gravity in the boiling pot pre-boil. You then multiply the points by the number of gallons collected and divide by the number of pounds of grain used. He said it should be around 30. Is this number the same if I do the same in metric? How do people get the efficiency percent? Also, I read of brewers only getting a certain amount out of their mash tun so they don't get their desired volume. Can't you just pour another x amount of litres into the mash tun so you do get the right amount? I know there are a few questions here, but this part of the process seems to be the most confusing and probably the most important.
Any help would be greatly appreciated.
Cadbury

[warra48]

The system described in Palmer's book is geared towards American measurements, and works in PPG (points per gallon).

It doesn't seem to be one used by many brewers, even on the US forums.

Here we tend to exclusively use the actual % extracted from grain as against a theoretical extract potential figure based on a certain tests (HWE test).

If you use a program such as BeerSmith, it will work in % efficiency as mentioned above, rather than Palmer's system.

You can work it all out manually, but it's a bit of a task. Here's how you can do it:

How it works is all malts and adjuncts etc give a different gravity.
The specs are all written as H.W.E which is hot water extract with sugar being the highest at 386 so everything else is given as a % of that. ie, pale malt is around 81% which gives you around 309. this is the total gravity you can get with 1 kilo in 1 litre but it is almost impossible to get this, this is 100% efficiency.
The same goes for American calcs but its in P.P.G which is the gravity of 1 pound in 1 gallon. The same specs are used ie. 81% for pale malt gives you 37 points of gravity.

So a simple example to work out total potential for 5 kg of pale malt in 23 litres is:
5 x 309 / 23 = 67 (1.067)

Now to work out your effiency, you divide the gravity you got with this brew. Say you got 1.050 so 50/67 =.74 you got 74% efficiency.
Then next time when you do the calc. 5 x 309 /23 = you simply times this by .74 .
This gives you your expected gravity.

For your first batches i would stick to using 60-65%.
So do the 5 x 309/ 23 = 67.
then times 67 by .65 = 43(1.043)

P.S. the HWE numbers are all on the malt craft site. Other malts like crystal malt are around 75%. Some malts can be lower and some higher.
To get the number times 386 by the percent as a decimal point ie pale malt at 81% gives you 386 x .81 =312

Ale -------81% X 386 = 312
Pilsner----------------81%
Hoepfner Munich----80% 308
Melanoiden--------- -80%
Caramalt pils---------79% 305
Crystal---------------- 75%

Say the HWE is 308 litre degrees per kilogram for a malt.
That means 5kg in 20L will give you : (308 x 5)/20 = 77. i.e. 1.077 SG at 100% efficiency. Multiply that by your efficiency (eg. 75%) gives you 77 x 0.75 = 57.75 or close enough to 1.058.

Hope it's not too confusing for you. If it is, spend a few bucks, and get a program such as BeerSmith, and let it do all the work for you!

[Cadbury]

I have read that table you are talking about. I am starting to get the idea and I have just downloaded beersmith. Thanks very much for going to so much trouble to explain the concept. I doubt if I could ever get a brew down without all of the help I've received over the last few weeks on this forum. Thanks again.
Cadbury