The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

The science of slow/cold fermentation?

warpatato's picture

The science of slow/cold fermentation?

Greetings. I am curious about the topic of slow fermentation, specifically the science behind it. What makes it interesting to me is just  by controlling temperature and the time of fermentation, you could maximize the flavor of the bread with very slight changes from the initial recipe.


How does it differ from the usual fermentation process? I mean in a standard fermentation, the yeasts consume the simple sugar created in the flour and gives off alcohol and carbon dioxide in a relatively short time as it is done at room temperature. How does lowering the temperature (via refrigeration) and slowing down the metabolism of the yeast and then allowing the bread to ferment for a much longer time affect the taste of the bread so much? What happens differently inside the bread done with fast vs slow fermentation? 


Though I do not know fermentation on a very specific level, I would really love to learn the more inner mechanics of it. Thanks in advance!

dabrownman's picture

of Indian , Pakistani,Thai and Mexican hot foods but when it comes to yeast breads I do't notice too much of a flavor or taste change by the making a poolish or retarding the dough but I do both for pizza dough which is about the only thing I make with yeast.  The best thing is that you can control the ferment and proof to fit your baking schedule.  Sourdough is different taste wise by using a temperature, hydration and whole grains to inprove teh flavor and kinds if acids made by the LAB. 

Salumeria's picture

That would be an interesting discussion. I've just successfully baked three loaves that had different periods of ferment, the longest being five days (and it was the tastiest). What I can report is that hubby, who has had IBS-D for the last four years, had absolutely no adverse reaction to the last loaf (slightly with loaf two, and a quite a bit of gas with loaf one which was a three-day ferment/proof). He cannot eat anything with regular yeast anymore. The science discussion would be very interesting to establish why the carbon dioxide in the long ferment is so much different to the regular yeast ferment (or if there is something else going on).

bikeprof's picture

While there are a number of folks who discuss how temperature changes the fermentation of the folks who makes a big deal out of it (esp. in the context of yeasted breads) is Peter Reinhart.  The Bread Baker's Apprentice is one of the places he talks about it.

Buehler's 'Bread Science' is heavily focused on chemistry, and also gets at a number of elements.  

I can't just rattle them off, but a table of the relative effects of specific temperature levels and the activity of different enzymes, yeast, and bacteria, would be a great resource...

Norcalbaker's picture

But the amount of starch that is converted and consumed by the yeast.

The underlying characteristics and flavor is a result of the wheat variety and terroir. Fermentation will enhance the natural flavors of the particular wheat, but also add other flavors.

The way Michael Kalanty explains it, there's four phases to dough fermentation:
1. Simple. Early stage of fermentation in which the yeast has converted and consumed very little of the starch in the flour. The dough will taste of straw, starch, and smell of yeast
2. Moderate. In this stage, a lot more of the starch has been converted to sugar and consumed by the yeast. The starch flavor gives way to a flavor similar to pasta or potatoes. The aroma evolves to more of a champagne scent.
3. Complex. Considerable amount of the starch in now consumed by the yeast. Flavors evolve to more earthy olive and minerals notes.
4. Over-fermentation. The starches are consumed. The aroma is beer or turned red wine, the flavor is bitter.



AlanG's picture

from a biochemical point of view.  One wants to maximize the length of the fermentation process.  In this way, one gets a variety of metabolites besides just CO2 which give the bread it's flavor.  This holds for both yeasted breads as well as levain/sourdough.  All of  Hamelman's yeasted bread recipes that I routinely use call for fermenting a portion of the flour overnight with a trace of yeast.  I've compared the bread prepared that way with the same recipe (ingredient wise) but omitting the overnight fermentation.  The former has a more complex flavor pattern.  Home bakers have the advantage of time and temperature that commercial bakeries don't.


Doc.Dough's picture

AlanG's observations line up with mine for straight yeast doughs.  But I can't tell you that I know what makes the difference.  There are a lot of biochemical processes running in parallel, each with it's own rate-limiting step, and each operating in a time-varying environment where there is a lot of co-dependence across the processes.

For sourdough breads, I have a better feeling for what is going on though the details have at least the same complexity as the yeast-only process.  With the addition of LAB to the mix, there are a whole lot of new potentially competing processes introduced.  The growth rate of the LAB as a function of temperature is different from that of yeast. And if you look at the pure culture growth rates as a function of temperature you will see that the LAB have a peak growth rate that exceeds the growth rate of the yeast.  And if you look at the low temperature end of the scale, you will find that LAB will continue to replicate (down to a pH of around 3.8) and (even below 3.8) produce acid at temperatures below the temperature at which the yeast essentially stop.  This produces a condition under which the LAB continue to produce acid from the residual nutrients in the dough while the yeast is almost totally dormant.  In general, the longer this goes on, the more sour the bread will be.