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Various fresh fruits, such as grapes, apricots, and dates, can be used to provide the yeast that is needed in breadmaking. But often in commercial production fruits are sprayed with pesticides, and then later they are washed, and therefore when they are sold in supermarkets they do not have much yeast left.

What fruits sold in supermarkets, whether fresh or dried, are most suitable for providing yeast for making bread?

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  • Are you looking to make a sourdough starter, or another application?
    – GdD
    Sep 6 at 12:08
  • @GdD - Not necessarily. But I'd be interested in answers that involve a sourdough starter as well as those that don't.
    – ruffle
    Sep 6 at 12:12
  • I would assume that production methods (e.g. non-treated, organic) are more influential than species?
    – Stephie
    Sep 6 at 13:25
  • There are certain fruits that are less likely to be washed, due to perishability (like grapes), and others that tend to be washed and waxed (like apples), and I want to say that might be related to wild yeast content, but I have no idea.
    – AMtwo
    Sep 6 at 17:46
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    I doubt you can harvest enough natural yeast from fruit to make bread. The process will surely require a starter to be created so that you propagate enough yeast and bacteria to leaven a loaf.
    – moscafj
    Sep 9 at 0:08
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Yeast on the surface of fruit and even flowers is a quite normal occurrence. For a start, I would recommend fruit that are commonly fermented for alcoholic drinks, so my first choice would be apples or grapes - also because they are quite easily obtained. Note that the yeast is on the skins, so using just peels or small fruit like berries or grapes is better.

However, any kind of “treatment” may interfere with the naturally yeasts on the skins, so I would recommend buying organic fruit and perhaps even skip washing them (ok, that’s probably debatable and personal choice). If you can get your hands on fruit straight from a garden or similar, that would be better than any fruit that’s been through a commercial packaging process and sat on shelves for a while. They may also have picked up mold spores that are harmless when you use the fruit as usual, but can increase the risk of failure for yeast harvesting. You also want fruit to be harvested as mature as possible, to get high sugar levels and subsequently high yeast levels - just to get things started faster.

During the recent Covid crisis and lockdown, some stores ran out of commercial yeast and while sourdough can be a substitute, yeast water had its renaissance, because it’s a faster method and can be made with fruit from storage. The probably most used candidates are raisins, but figs, dates and everything that gets dried with the skin can work. Note that raisins have a particularly high surface to volume ratio, so the yield is quite good. Apart from making sure you get the skins (which is theoretically enough, you don’t need the flesh for yeast), you also want untreated pure fruit, so neither sulfur-treatment (for „brighter“ fruit and preservation) nor those poached in sugar, like it’s often done for cranberries and other sour fruit. Not part of your question, but maybe worth an experiment: some flowers have a high yeast content, so soaking a few elderflowers in sugar water gives you the same results as the raisins, but it’s a seasonal thing - and I have read (but not tested) about linden and sunflowers as good nectar yeast sources.

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  • +1, except I would doubt the apples - they are quite frequently treated (including the organic ones, which get waxed).
    – rumtscho
    Sep 13 at 9:40
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    Apples may depend on source - if they aren’t washed (-> stripped off their natural wax), there’s no need to add artificial wax. It’s also country-specific: Apples produced and sold in Germany are rarely waxed and it’s not permitted for organic apples. Other regulations may apply elsewhere. The US allows waxing for organic fruit, but limits the kind of wax. For some cultivars the natural wax layer is thicker, so there’s no need to add any. That may be worth further investigation.
    – Stephie
    Sep 13 at 9:43
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A possible answer that is very practical for those who shop in British supermarkets is bilberries. These tend to be covered with a white powder which surely almost certainly contains a lot of yeast. I am in the process of testing this hypothesis.

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  • So, how did your experiment turn out?
    – Stephie
    Sep 13 at 8:12
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Dried persimmon have a white bloomy coat or soon will after purchase.

This gal produces 'water yeast' for baking; details about her attempt with persimmon:

https://www.thefreshloaf.com/node/49639/park-tae-young-yeast-water-chronicles

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    I would suspect that the white bloom on dried persimmons are sugar crystals? - Yep, the article says so too.
    – Stephie
    Sep 13 at 7:14
  • Ate a lot of them in Beijing; yeastie beasties. Super gross when it gets thick and dusty. Can just scrape and rinse.
    – Pat Sommer
    Sep 14 at 2:51

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