Teaching the sourdough method in a 6 hour workshop

is to build whatever quantity I need for the students' breads, plus for my own demonstration bread, prior to class.  Since my students typically have no prior sourdough experience, I also prepare enough starter (50% hydration) for them to take home and maintain.  The former amount can be quite a lot of material, depending on the formula and the number of students involved.  I think the rye bread class that I posted about back in January required something in the neighborhood of 20kg of starter.  This past Tuesday I took enough starter for the English muffins, which weighed about 12kg at 100% hydration.  The stiff starter for the students to take home is parceled out in 30-50g chunks, so it's a much smaller quantity.

For a 6-hour class, assuming ambient temperatures are somewhere above 70F, the students should be able to mix, ferment, and bake at least one type of bread in class, with another one or two types mixed and retarded to bake at home.  I provide plastic bags for the take-home dough and the stiff starter.

There's no reason to discard half of the starter while you are building it.  Just add a quantity of flour for each successive feed that is at least as much as the beginning weight of the starter that is ready for feeding.  For instance, if you have 600g of starter from the previous feeding, feed it 600g of flour (or more) at this feeding.  Do build more than you expect to use; there is always some loss as you empty the container and it never hurts to have some extra on hand in case there is a spill.  You can always take the excess back home for your own use.  (This from the man who has 40+ English muffins bagged and sitting on his counter as of this writing.  In all fairness to myself, the overage was deliberate in the anticipation of additional students that did not sign up after all.)

You are on the right track to provide for everyone, rather than assuming that all will come equipped.  And your math stacks up, so far as I can see.

Have fun!

Paul

I'm no expert, just a home baker, but I've read many books and made 50 or so loaves of sourdough bread. So what follows is simply what I now believe.

Your arithmetic is right. 100% hydration starter favors lactic acid (80% favors acetic acid, 120% favors yeast; the Germans do all three stages). Feeding once a day is what one tells people or they'll never start; twice a day is better before using the starter for bread. One wants to catch the starter on the upswing, at a healthy peak. Too old will give less rise and poorer gluten. While San Francisco is famous for "no doubt" sourdough, the French believe this to be sourdough gone wrong. (i'm reminded of the American obsession with breast size and barbecue smoke; we're afraid of making mistakes.) For French "levain" one teases the starter to not dominate the taste. One can do a few starter refreshes as close together as six hours, three hours before making bread, but this leads to longer bulk and proof times.

A six hour class is very tight for making and baking sourdough bread. Consider adding a bit of diastatic malt powder and a bit of commercial yeast, for shorter rises and better oven spring. Be sure to pick a fairly warm proofing environment. Then, Hamelman is encouraging on the use of short (a couple of hours) bulk and proof times for sourdough breads. One's usual intuitions may lead one astray, to overproofing.

Half starter is a lot! I use 15% to 20% (baker's percentage, by flour weight). More, and one is into a specific bread recipe's preferment stage rather than refreshing the starter.

The risk with sourdough is always that of making flying saucers. 62.5% hydration is much stiffer than my experience (near 72%), so you're probably safe. I knead by hand and fold during bulk, expect a scary bit of slack on the way to the oven which springs back with ample steam.