Here, at the last step of the process before filling and storage, I could see only the tops of the three-story tall kettles, but I noticed a small window in each one, through which the swirling mass of liquid C was visible. I asked about the portholes, and the answer was this: “After the mixture cooks for a set time, it needs to reach the right viscosity before it is ready. But we can’t really measure viscosity. So the chief engineer goes out and inspects the batch through the windows. He can tell by how the liquid flows when it has reached the right point, like a master chef knowing when the sauce is done.” This remained, and as far as I know, still remains the approximate standard for judging viscosity directly, though as the AAPS NBC speaker mentioned, other indirect methods may often suffice. I have heard similar tales from engineers in other industries where “cooking” the product, such as plywood glue, requires the human touch to know when the batch has reached the point of being perfectly viscous.
The relevance? Today’s technology still mainly aims for perfection only indirectly. The AAPS show was full of examples in which measurements of key conditions rely on “markers,” i.e., parameters that vary as a function of the measurement target — often a qualitative state such as purity or stability. The situation is analogous to drug development, with its contemporary use of biomarkers, genetic tags, and the like. (It is also a microcosm of the life science sector as a whole; a maze of differential approximations guiding but not determining human decision-making.) Characterizing a drug as a substance thus bears a close relationship to characterizing it as a therapy — sometimes a crazy-looking dance around many obstacles and diversions toward the ultimate goal. Until computers and production robots become indistinguishable from us in perception and judgment, and can therefore “look” at the swirling mass and know when to declare the cooking “done,” the viscosity dance will always require a combination of imperfect technological solutions and good ol’ human skill, interaction, and intuition.
(Please look for my full report on the AAPS National Biotechnology Conference in an upcoming issue of Life Science Leader.)