Mr Gilbert said it took a few weeks to build it up to usable quantities, but his first bread made with it was on sale at the weekend.
It was interesting to compare it with his regular sourdough, which he makes with a starter he captured about five years ago when he owned Charlotte's Bakery.
He said he made the two breads the same, except for the different starters.
The San Francisco bread had a different texture from his regular sourdough, a looser crumb with more air holes, and perhaps a slightly milder flavour than the sourdough bread he already makes.
A true sourdough bread does not have commercial yeast added but uses a starter dough which contains a culture of yeast and bacteria which may vary from place to place or bakery to bakery.
Some sourdough cultures go back a long way.
Each time one is used, it is aerated and fed with more flour and water to build up quantities before the next batch of bread is made.
Some of the starter dough is included in each batch of bread, which is given a long proofing time to allow the bread to rise and ferment.
Sourdough bread generally has a different flavour and texture from regular yeast-raised bread.
According to Harold McGee in his magisterial On Food and Cooking, the acids in sourdoughs make the bread resistant to spoilage microbes, "so sourdough breads tend to be especially flavourful and keep well".
