(Josh, you actually don't see L°/kg here much. Anyway, below I am going to try and put things together a bit.)
Like most areas of brewing, the lack of standardisation makes things very confusing. You can see this from the metric versus imperial posts we have had here already. It actually gets even more confusing. For example, extract potential can also be expressed as a percentage. I'm going to try and tie all these together towards the end of this post.
Before we even get there though, we have to address the laboaratory methods and some of the terms used that relate to extract potential. I am not even going to mention some of the methods of measurement such as CWE (used by some British Maltsters) and will only touch on coarse grind as I think the below is bewildering enough for most brewers
.
This extract potential area is a great example of how ridiculous non-standardisation is and how rife it is in the brewing world. Drives you mad!!!!! Are you still with us wbosher?
Here's Part 2...
[center]
How do I Find out the Extract Potential of a Fermentable?[/center]
Unfortunately there is no common standard (let alone language) used by maltsters of different countries let alone in the same country to describe the extract potential of a grain. Perhaps the easiest things to keep an eye out for in most malsters specs are the following...
MC - Moisture Content
All grain contains some moisture. Four percent is a rough average. So, if we bought 100 kgs of grain and dried it out, we'd end up with 96 kgs of pure grain matter. Grain that has been dried is referred to as being on a "dry basis". Grain that has not been dried is termed, "as is."
Nearly all laboratory tests use grain that is on a dry basis.
FG or CG - Fine Grind or Coarse Grind
To confuse us even more, a few malsters use grain that has been coarsely ground instead of finely ground. A coarse grind is seldom used so I suggest we don't even address it here. Just be aware that if you ever see anything like CGDB or DBCG, it means Coarse Grind Dry Basis.
FGDB versus FGAI - Fine Grind Dry Basis versus Fine Grind As Is
Putting the above information together, you will often see the shorthand FGDB and MC in grain specs. FGDB (or DBFG - note that there is no standard in these extract potential terms as to whether the grind or the basis is written first) means a fine grind was used on grain that had been dried for the laboratory extract potential test.
As we are not using dry grain in our brew, we must convert FGDB to FGAI. You do this as follows...
FGAI = FGDB * (100 - MC)/100 eg 96 = 100 * (100 -4) / 100
[center]
FGAI - Imperial, Percent or Metric?[/center]
In my posts here, I have only referred to the extract potential of a grain or fermentable as being expressed in ppg. As mentioned first thing in this post, a maltster may also choose to express extract potential in metric or as a percentge. Let's firstly look at what ppg means...
PPG = Gravity Points per Pound of Fermentable Per Gallon
What this is saying is that if the extract potential of a fermentable was say 37, then if you put a pound of this fermentable into a gallon of water and then checked the gravity with a hydrometer, the hydrometer would read 1.037.
Note that sucrose is regarded to have an extract potential of 46.214 points. So if you dissolved a pound of dry sucrose in a gallon of water, your hydrometer should read 1.046.
Percent = Extract Potential when compared to Sucrose
We saw above that sucrose's extract potential when expressed in PPG is 46.214. Sucrose is considered to be fully fermentable and therefore if it's extract potential is expressed as a percentage, it is expressed as 100%.
If we know the extract potential in ppg but wish to express it as a percentage, we simply divide it by 46.214 and multiply by 100. So, if our specs said our grain had an extract potential of 37 ppg then it's extract potential as a percentage would be...
37 / 46.214 * 100 = 80.1%
Metric - L°/kg (referred to as HWE or Hot Water Extract)
Unfortunately, here again we see no correlation in logic to the imperial ppg. L°/kg means how many litres of wort with a specific gravity of 1.001 you could produce from a kilogram of the fermentable
.
For example, if you had a kilogram of sucrose, you could make up 386 litres of wort with a specific gravity of 1.001.
To convert L°/kg to a percentage, divide it by 386 and multiply by 100. For example, if your grain had a L°/kg of 309, then it's extract potential as a percentage would be...
309 / 386 * 100 = 80.1%
Expressed in ppg, it would be 80.1% * 46.12 = 37
See how joshua's post above also relates to this? 309 / 8.3454 = 37
...
Wouldn't it be nice if all specs were just expressed as a percentage using the same laboratory method?
A Few More Things
1. The only way to get true specs is to get a copy of the specs that came with a batch of malt. Every batch of malt varies and you'll find it hard to get a hold of the specs for all the fermentables you use.
2. Whilst the Calculator doesn't allow for the input of individual fermentables extract potentials, the default average works quite well unless you have a large amount of sugars in the recipe. The BIABAcus, which will replace The Calculator, does allow you to over-ride the default average for every individual fermentable however, for an all-grain recipe, especially considering 1 above, I wouldn't bother doing this. It doesn't make that much of a difference.
3. Be aware that some popular brewing software has extract potential wrong. For example, one does not account for moisture content so their gravity predictions are about 4% out straight away. From memory, the same program 'forgets' to shrink the wort on their pre-boil gravity meaning that EIK reads higher than it really is. So, there are a few errors out there.
I know we haven't even looked at adding up all the individual extract potentials in a grain bill. The above examples have just assumed a single fermentable. Let me know if you want an example of working out a full grain bill's extract potential and I'll write one up but won't have time to do so for at least several days.
Fun and games
,
PP