Go back to the beginning of this topic and read the first post from Kephra. Thats where the change came from and Kephra explained it.
The numbers don't add up and Kephra is being cautious which is something we should all be cognizant of.
Karo is organic. Who knows when the last time the manufacturer updated their label was or if they even test batches to verify the analysis (I'm thinking not). Who knows whether the analysis on the label was ever correct? A lot of times, manufacturers are trusted in what they say and nobody in our government checks. With a LOT of things. Who knows, if they're not testing each batch, what the variability is for the product from batch to batch? They can't be getting all the corn they use to produce it from the same place and even if they do, crops vary from year to year or even sometimes from crop to crop.
We basically know nothing other than what the label says but as Kephra points out, when you go through the analysis, something does not compute.
Glucose is perhaps the only reducing sugar we can nail dead on because glucose is glucose and if its glucose its always glucose and never varies and the science works. Karo? Maltodextrin? Cinnamon extract and others? Who knows?
For sure with Maltodextrin, given it varies based on dextrose equivalency (if you know the DE you could compute it exactly), where the stuff available in the US anyway is mixed bag where there is no stated DE number, the ONLY thing you can do is compute how much for the worst case DE number (fewest reducing groups, longest sugar molecules) and go with it knowing it will never be this bad so you're safe. You can't ascertain anything else.
Yup, clear as mud.
Our goal here is to use ENOUGH reducer to guarantee ALL the silver oxide is converted to colloidal form, if even that means we have to use an excess of the reducer to guarantee this. Sadly, because accurate chemical analysis's of reducers other than glucose aren't really available all we can do is figure out what enough is and go with it, now not needing to cross our fingers.
Also, for your example, 320PPM, 250ml where you're using 5 drops, do you think, if you lucked out and got a "good" batch of Karo that you'd be able to tell if you were able to reduce 310PPM of silver oxide with it? Do you actually think that when you dilute that down to 20PPM you'd even notice a difference? That'd be 0.625PPM at 20PPM dilution unreduced silver oxide. What about 20PPM (300PPM reduction) which would be 1.25PPM silver oxide? I kind of doubt it.
Taste is a gross indicator that you're close, not dead on. And then too, everyone's sense of taste is different and worse yet, taking things like Asprin will reduce your senses sensitivity (including taste) by at least 20% (proven). Something to think about.
Plus, for having an excess of reducer, the density of sugar molecules is greater meaning there are more reducing groups near each silver particle which guarantees a better chance of reduction and also faster reduction because the reducing sugar molecules don't have as far to travel to find a silver oxide particle to reduce or the silver oxide particles don't have as far to go to bump into a reducing sugar molecule.
This is all seat of the pants with as much science as we can wrap around it. Given the nature of the beast, it will never be exact so you go with extra to guarantee you're good no matter what and call it even.
More reducer never hurts and with Karo, you'd be hard-pressed to taste anything. Maltodextrin, given how much we have to use to guarantee that a worst case will still reduce all the silver oxide particles you will potentially taste. Cinnamon? Absolutely! Perhaps others.
And at least for sure, with cinnamon extract, given the distinct flavor, it may mask an incomplete reduction if you don't use enough.
Like I said, clear as mud. A lot of this is a guideline, not an absolute but all you can do is the best you can and go a little extra to cover things and call it even.