My favorite eggplant is Rosita. It's gorgeous. I'll show you pictures when my fruit that are currently swelling and coloring are harvested. But despite how special it is and how well it grows in my yard's climate, some years, it's nearly impossible to find commercial sources of seed for it. That's just one of the many reasons it's important for me to save my own seed.
My friend Loretta at Spade and Seeds gave me a Thai Long Green eggplant seedling this year, now growing in the same bed as my Rositas. It's a nice eggplant, too: productive, pretty, and mild. The seedling she gave me blossomed well before my Rositas, the only other eggplant variety in my yard (or on the block, for that matter), so I knew the first fruit it set was isolated and would produce true-to-type seed. I decided to save seed from that fruit to give to her as a thank you for the seedling.
So, I let it grow. And grow. And then it became firm and turned from its lovely soft green to a vibrant gold. The mature fruit means that the seed is now mature as well.
Once I picked it, I brought it inside my shed to work. Though you could do it this way, it'd likely be very tedious to dissect an eggplant, using tweezers to dig out every small seed. So, I tried to be more efficient. Using a box grater, I grated the bottom third of the fruit into a large bowl. Grating the flesh loosens it up enough for the flesh to separate from the seeds. Checking to make sure I had grated all the flesh that held seeds, I poked around in the flesh above the bottom third of the fruit, but the only seeds to be found were in the bottom.
I added some water the bowl to help separate the flesh and the seeds even more. The flesh floats in water, while healthy seeds sink, so the two fall away from each other. Here, my summer intern is holding the bowl up to the shed's ceiling so you can see how the seeds have settled on the bottom of the bowl.
We used our bare hands and scooped up most of the floating flesh. Some still remained, so I added water, swirled the mixture together, and while swirling, carefully poured off the water and the floating flesh. That left us with almost-clean seeds.
After another couple swirl-and-pours, the seeds were completely free of residual flesh.
We plopped the seeds on a labeled sheet of parchment paper (the seeds won't stick to it as they dry).
When they're completely dry, I'll package them up and give them to Loretta. She'll be able to grow quite a few children of her gift to me next year. Later this summer, I'll repeat the process for an isolated Rosita fruit. Never will I be unable to find seed for my favorite eggplant.