LMSC MWJB Is 400um the base for filter to identify the % distribution of fines ? If I remember correctly, I think you wrote the ideal range of fines is 9%-12%. Thx
Not 400um, ‘400 Kruve’. This is because Kruve 400 uses holes that might be 400um across but they are round, not square with different spacing to an ASTM sieve, so you don’t get the same results if you switch from Kruve to ASTM. Sorry if that seems pedantic, but mixing these will seriously skew results.
Also, I’m not considering nor identifying these as ‘fines;’ All the Kruve sifters come with a 400 in the bottom, even the 2 sieve set, so I choose to use 400 Kruve as a reference as everyone who has a Kruve can compare (personally, I’d like to use a larger, easier to clean sieve). There is no technical reason for this choice, just the desire to make any measurement as widely meaningful as possible.
The % range of usable grinds that you can get below 400Kruve is wide, from 7% to 24% depending on how you are going to brew (just that I know of). 9% is a specific target for given recipes. 12% is another target for different recipes, You wouldn’t really treat them as a range for a single recipe/regime. For any recipe the grind should be specified* , otherwise the rest of it is meaningless and you have to hunt for it.
*In a more meaningful way than “coarser than I use for 2 cup V60”, because we don’t know the start point, how big a cup is, or how fast the pour is, etc, :-)
As for what is a “fine” specifically, I don’t much care, it must be such a tiny part of the ground mass as to be of no influence in drip brewing. All grinders make them at all settings. If you want less small bits (say less % under 400 Kruve) in your grind, set your grind coarser.
We don’t even know that fines have a negative impact in drip brewing, at least any more so than the largest %.