I would think that the starter should have sufficient sugar content to get the colony building going. But also we do not want to introduce factors that shorten the yeasts life, like yeast death due to high alcohol, or osmotic stress from high sugar levels. From that perspective would you still recommend going with a starter Brix above what might be in your juice?

Stop making sense! You're confusing me!

I'm thinking out loud here ... using a 240 ml size (rounding up) 12-14 hour starter as the model, if we use too little sugar, it will be consumed before morning. Go with too much sugar, and osmotic stress could be a problem. In 12+ hours, I don't expect high ABV will be a realistic problem, but if we put a cap on the brix, it won't matter.

If my calculations are correct, 2-3/8 Tbsp sugar provides 13 brix, +/-1 allowing for less than careful measuring. This eliminates osmotic stress as a problem, so it comes down to "can the growing colony eat that much sugar in 12+ hours?". Let's not focus too much on the brix -- we're considering a tiny sample (in relation to 23 liters) with a large amount of yeast (5 g) which is designed to inoculate up to 23 liters of must.

My take on this?

Calculations are not going to help nor is conventional wisdom. We need a practical experiment that starts with the above and measures the SG after 12-14 hours. If we have more than 10% sugar remaining, then 13 brix is fine. If we have more, it's still ok. If we have less, then we need to consider adding more sugar to the starter.

The fun part is figuring out how to measure SG in a 240 ml sample using normal home winemaker equipment. The only thing that comes to mind is a refractometer and using the translation table to determine the actual brix.

But you **also **need sufficient nutrients. If you do an overnight starter with just sugar and water, the yeast might run out of nutrients and produce H2S.

I add 1/2 tsp Fermax to my starters, so that's not a problem for me. However, it is something everyone should consider.