Living Traditions Homestead posted this video several years ago. Heart of your question is answered around the 12:30 mark, but I'd recommend watching the entire thing.  BTW, the channel boasts 413,000 subscribers. Worth watching in my opinion.

Edit: In August, LTH updated their method of making sauce.  I think the "juice" would be too thin for my taste, but would make a wonderful base for vegetable soup.