Hi Ozzie
I'm pretty new to this game but I do have some thoughts on measuring tiny amounts of Penicillium Roqueforti (or any other culture for that matter).
The first Stilton I attempted went entirely blue within about 3 days, as did the next. My problem was that I followed the recipe which stated I should add 1/8 teaspoon of the culture.
Having had the same problem twice I figured something was wrong so I had another look at the packaging and realised I had about 1 teaspoon left but the entire batch was enough to treat 500 litres. I had overdosed by a factor of about 6. I realised that there was no way I was ever going to be able to accurately measure the correct amount for a 6 litre batch
My solution, and no doubt the purists out there will shoot me down in flames, was to dilute the culture with powdered baby milk formula. (I only used the baby milk because I could not source normal dried milk).
I measured the amount of culture I had left and added several teaspoons of the dried milk and mixed it well. I can't remember the exact quantities now but basically I worked it so that when my recipe calls for 1/8 teaspoon that is what I add. Because it is diluted what I am actually adding is something like 1/50 teaspoon of Penicillium Roqueforti and about 1/8 teaspoon of powdered milk.
I figured, rightly or wrongly that adding that tiny amount of dried milk would not really make any difference particularly as it goes in right at the start and 1/8 teaspoon dried milk diluted in 6 litres of fresh milk was virtually insignificant.
All I can tell you is that my next effort, using the diluted mix worked out fine.
Guiseppe