I had settled into a habit which had quickly become unthinking: using the Baratza Encore grind setting of "12" for my vacpot brews with the C30C. I had tried a setting as fine as "9" once or twice before and decided that the grind was too fine. In retrospect, I think I had no good reason to move back up to a coarser setting. I probably made a pot from insufficiently rested roast and wrongly blamed the unrested flavor on the grind size. Then there were a couple of pots that had some sediment, which in my mind I may have blamed on grind size but which in reality were due first to a twisted portion of the filter screen gasket and then to there not being enough spring tension holding the filter in place. I remedied that gasket problem, then the spring tension problem, but still didn't try to grind finer. Additionally, a different bowl that I briefly tried caused a small vacuum leak between the bowl and the funnel which I could not detect at first, and the drawdown was faster, causing further delay in identifying that there was a vacuum leak because I saw no reason to equate "faster drawdown" with "vacuum leak". In some unknown mental process I credited larger grind size with faster drawdown even though the faster drawdown was caused (counterintuitively) by the vacuum leak. Last but not least, there's the distinct possibility that a 2nd opinion has influenced my assessment of brew quality.
Over the weekend, a desire to make a stronger brew for my brother shook me out of the "12 size grind" habit and I used "8" for 3 pots. There is a pause in the drawdown process, after about 2/3 of the liquid has returned to the bowl from the funnel, but this pause has always existed regardless of how fine or how coarse I grind. Results with the smaller grind size were excellent, causing me to think: why stop there?
I'm currently enjoying greatly a pot made with grind setting of "6", despite the fact that the coffee was roasted only 10 hours ago. Hmmm... no sign of overextraction or sediment. In fact, I'm thinking if this Brazil Fazenda do Sertao Lot 50 is this good after 10 hours, how great is it going to be after more rest?
Guess I'll try a grind setting of "5" for the next pot. Lessons to be learned?: I dunno. Knowledge to absorb?: only if you find some. My observations are strictly empirical, subject to change, and as you can see I sometimes draw incorrect conclusions from those observations.
I'll mention once again that I really love the 50+ year old C30C vacpot, the effectiveness of its very fine mesh metal screen permanent filter, its fully automated process and the metal construction which obviates any worries about implosion or breakage.
Roast: Behmor 1600. Grind: Baratza Encore. Brew: Behmor Brazen.