Reasons my sourdough attempts failed?

Question

Last March I started adventuring into the world of Sourdoughs by following the advise of The Fresh Loaf Bakers's handbook but using wholegrain rye flour all the way and it went pretty well; after a week or so I started having nice sour rye breads. For context, this was a typical spring in Mallorca, known for its usual high humidity, with temperatures at home between 18-20ºC to about 30ºC by the time I left.

Then, I moved to Vigo (northwestern Spain) in the middle of July and sure shortly after I decided to make a new sourdough from scratch following the same recipe, but this time no orange juice.

For context, I set up a humidity/temperature sensor and got some values ranging 70% and 99% (crazy weather here) and intense 29-32ºC at home. The result was a rather smelly (and not in a good sense, nowhere similar to what I had before) sourdough after a few days, which after four or five days developed a thin white layer of something I thought would be mold.

I had searched for this at the time and found it might be mold, so I discarded it. Then I said to myself, it must be the orange juice, so I went and tried again with orange juice only to obtain the same results. This experimentation process went for about 4 cycles.

I tried feeding it twice a day, I changed the jar in which I was keeping it, I covered the jar, I uncovered the jar, I sealed the jar, all to no avail. By then I decided not to waste more time and wait for colder climate maybe (haven't done so yet, though).

Now I'm thinking I want to start again, but I'd like to get some feedback from more experienced users into what might had gone wrong. I even started to suspect it was related to the quality of water (which I purify with one of this Britta filters, any thoughts?) or of the air.

For reference: my sourdough would get a layer, not as bad, but close enough, to this: The Fresh Loaf post

Answer 1

The temperature is indeed the most likely reason behind it. In sourdough, you are creating a small new ecosystem niche, and depending on the environmental conditions, different strains of yeast and bacteria will "win" and outgrow the others. And for microorganisms, there is a huge difference between the 18-22 C when your successful colony established itself and the 32 C when you made the second try.

The air humidity is less important, since it is the humidity within the sourdough itself that drives the growth of the microorganisms. There may be a small effect in the initial seeding, with different microorganisms drifting in the air in the different climates. However, I am not sure how much that matters - there are all kinds of conflicting information out there on where your microflora comes from (air or not) and how much influence it has on the final outcome.

I don't think there is much you can do about the whole thing, if you cannot control the temperature. I am not aware of sourdough recipes developed for fermenting at 30 C. If you want to use this recipe, you will have to find a temperature-controlled environment at the right range. Assuming that you don't have that, but have a fridge, you might alternatively try a recipe intended for starting in the fridge. These will give you a different style of sourdough, you will have to decide if you like baking with it.