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What is the technical difference between fermentation and leavening? Both cause bread to rise.

  • Does fermentation only refer to the chemical process of one substance converting to another, which causes bread to rise?
  • And is "leavening" rising by any means?
  • Classic white bread, for example - it undergoes fermentation. Does it also qualify as leavening? Whereas banana bread undergoes leavening, but not fermentation?
  • Hello JLandsberger, you almost nailed the way to make a list. You need to leave an empty row under the last paragraph and the first list item, and then an empty space after each dash. Look at the source of the edited question and you'll see what I mean. – rumtscho May 12 '15 at 18:34
  • Thank you. I looked at the html as well, but was getting a bit frustrated after I tried it about five different ways and couldn't get it to list right. I'll note this down. – JLandsberger May 13 '15 at 22:42
  • Ah yes, I know this kind of frustration. Markdown just happens to be one of those computer languages which are easy to read but hard to write. For the most common stuff, you can use the formatting buttons over the posting box, they insert properly formatted markdown for you. You can also read the short tutorial, cooking.stackexchange.com/help/formatting, or follow the links in it to the official specification. These have saved me some headaches in the past. – rumtscho May 14 '15 at 9:16
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Leavening is rising by any means, so baking soda and baking powder (chemical leaveners) both apply here, as does yeast (fermentation).

Chemical leaveners like baking soda and powder work by mixing an acid (varies, depending on the recipe) and base (usually baking soda in some form) to produce carbon dioxide gas.

Fermentation is the process of yeast converting sugars to carbon dioxide and alcohol. In bread making, the carbon dioxide is the desired product. In beer or wine making, the exact opposite. In both cases (beer/wine and bread), other byproducts produced by the yeast add flavour and are highly desirable.

There are other types of fermentation by bacteria (such as those used in yogurt-making, pickles, or sauerkraut) that produce lactic acid; but those are somewhat outside of the scope of this answer (although lactic acid fermentation by bacteria is responsible for the taste of sourdough breads).

To specifically answer your question - yes, yeast breads undergo fermentation (which is also leavening). Quick breads like banana bread use chemical leaveners, which are not fermentation.

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    Great concise answer. I would only clarify that fermentation is also a more general process that can also involve bacteria and result in various byproducts (gases and alcohol as you mention, but also acids). In the context of bread in this question, fermentation can produce not only leavening in the form of gas but flavor as well in various chemical byproducts (most noticeable, for example, in sourdough where fermentation produces significant acidity). – Athanasius May 12 '15 at 18:06
  • True; I didn't want to confuse the matter by adding lactic acid fermentation by bacteria to the mix, or the intricate details of the different types of yeasts (e.g. brettanomyces yeasts) that can yield very different characters due to their other byproducts, so I stuck within the confines of the specific question asked :-) – Chris Macksey May 12 '15 at 18:09
  • I've edited to add a bit more context, hopefully without adding confusion. – Chris Macksey May 12 '15 at 18:11
  • If you have a fast rise from yeast, although there is some fermentation happening, there's so little of the chemical byproducts that many people might not consider this to fermentation. (it's an issue of how you view groupings -- are we going with classical categories a.la Aristotle, or more fuzzy categories a.la Lakoff – Joe May 12 '15 at 18:16
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    Athanasius : it's fermentation, but when someone mentions 'ferment', you picture in your mind something that typically takes a long time and imparts significant flavor or structural change -- saurkraut, cheese, sour pickles, kimchi, sourdough, beer, wine, etc. Wonderbread and the like are on the far fringes of the category as although the yeast might've eaten the added sugar, it hasn't had a chance to act on the starches within the wheat ... so it's barely fermented. – Joe May 12 '15 at 18:30

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