The Fresh Loaf

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Effects of Sugar and Fat on Fermentation

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bshuval's picture
bshuval

Effects of Sugar and Fat on Fermentation

Hi all, 

I am wondering why so many people erroneously assume that (a) fat inhibits fermentation, and (b) sugar increases fermentation. 

When I tell people that sugar (in concentrations above 10-12%) inhibits fermentation because of its hygroscopic properties, they look at me funny and dismiss it (although perhaps the word "hygroscopic" is the cause for that funny look). Their logic is always: "yeast loves sugar. More sugar = happier yeast. Happier yeast = faster fermentation". 

With fat, the opposite happens. People automatically assume that doughs with high proportions of fat are "heavy" and ferment slowly. This, again, is wrong. Fat has no effect on fermentation. "Try making a brioche" I say, to no avail. I think that often doughs with large amounts of fat also have a lot of sugar in them, which is the yeast inhibitor. People, however, are sure that sugar can't be the yeast inhibitor -- so fat must be the culprit. 

What are your thoughts on the matter?

thomaschacon's picture
thomaschacon (not verified)

...is to get too happy with the molasses or the malt syrup. 

How many loaves of fig-anise bread have I killed with "Oh, I bet molasses would be a great addition!" Bzzzt. Wrong. Result: Fig-anise bricks.

Graid's picture
Graid

Interesting, I completely thought it to be the case that sugar would increase fermentation, to the extent where less yeast is needed for sugary breads and vice versa. I've always found that sweet doughs- challah, brioche etc rise very well and very vigourously. Never heard anything about fat affecting fermentation though, only sugar, salt, and yeast. Too much salt inhibits the yeast, too much sugar will overfeed it, was what I thought.  I thought that 'overfeeding' would lead to overrising and collapse though. 

gary.turner's picture
gary.turner

The problem arises from the alcohol and CO₂ excreted in the fermentation process. Both inhibit the yeast's health and appetite. The CO₂ is reduced by stretch/folds or punch-downs. The alcohol remains. At some point at about 10% alcohol, the little beasties become inebriated and lose their appetite and maybe their lives. Now the weight of alcohol is very close to the weight of sugar (CO₂'s weight being trivial), so the limit is somewhere around 10% by weight of sugar. Effectively the yeast is drowning in its own excrement.

Brewers wanting very strong beers, 10–15% alcohol, e.g. Russian Imperial or other barley wines, have gotten around this limit by using yeasts that are more alcohol tolerant. The usual source for this is wine yeast (from berries rather than grain).  Even these alcohol tolerant yeasts are slowed, but not killed, by the alcohol. It is not uncommon for the secondary fermentation very strong beers to take upwards of 18 months, and after krausening and bottling to take another 2 years to reach maturity.

cheers,

gary

davidg618's picture
davidg618

Sugars, indeed, above as little as 5% will draw water away from yeast cells, slowing fermantation. There are a couple of easy solutions: 1.) Increase the amount of yeast, or 2.) use osmotolerent yeast; SAF Gold is one well-known brand. For sweet doughs, I prefer to use osmotolerent yeast. Commercial yeasts contribute very little flavor--I can't detect any in properly dosed recipes, but I've friends that claim they can. Consequently, when I use commercial yeast, I use as little as practical.

An aside: I've not found a reference online to support the following thought; nonetheless, I wonder if "yeasty flavor" results from dead yeast cells (depending on its age, at least half the dried cells in Active Dry Yeast aren't) and/or coatings or stabilizers added to yeast. Obviously, there is some increase in the quantity of live cells during fermentation, but no increase in the quantity of dead cells, or inert additives.

Fats and Oils: I make Sourdough Biscuits routinely every seven to ten days. Unlike many SD biscuit recipes that employ baking powder, my formula relies solely on natural levain for leavening. The fat content, a 50/50 mixture of butter and lard, is 28%, while the ripe levain content (@100% hyd.) is 129%! Despite the relative large amount of ripe levain, repeatedly the biscuits take approximately twice as long to proof, compared to lean dough breads made with only 30% of the same ripe levain.  I have always suspected this decrease in leavening is due to the high fat content.

Your post prompted me to look further. I found this in Google Books:

"Adding fats and oils in the process of bread-making produces a greasy effect in the dough fermentation, helps increase the extensibility of the gluten, is conducive to the volume expansion of the dough, increases the volume of breads, and contributes a refined texture and softness. The most appropriate amount of fats and oils to be added in general recipe for white breads is 4-6%, but for sweet baked goods, the ideal proportion should be 8-10%. Too much fats and oils will not only inhibit the extensibility of the gluten and expansion of the dough, but also cause a portion of the yeast to be surrounded by an overabundance of fats and oils, rendering osmotic function impossible. This makes the fermentation process extremely slow and results in incomplete fermentation of the dough."

Reference: Bakery Products: Science and Technology, By Yiu H. Hui, Harold Corke

nicodvb's picture
nicodvb

osmotic pressure is the key. Sugars are detrimental to the rheology of the dough, but they are equally harmful for the yeasts

I also found a couple of papers describing an unexpected positive effect of salt on yeasts: a 2% salt respect to flour exhibited a higher production of alchool and CO2. Yeasts methabolism continued up to 8% salt.

davidg618's picture
davidg618

During the past six months, I've been tweaking the techniques I use making my three most often baked formulae: a 90/10: white flours/whole rye flour sourdough; a 50/50: bread flour/whole wheat flour sourdough; and what I've called Overnight Baguettes, a retarded straight dough of 100% AP flour, and varying (65-72%) hydration. I make 2, 1.5 lb. sourdough loaves, and 3 baguettes every week to ten days--more if we're entertaining. I've had lots of opportunities to hone techniques.

All of these formulae are made with "standard" 2% salt, and I've settled on a 1 hour autolyse with DDT set to the retarding temperature (54°F) or a 35 min. autolyse for "quickie" unretarded loaves with DDT at 76°F, regardless which formula I'm baking.

So far, all of this is pretty close to the gospel according to the experts and TFL: except I add the salt to the mix from the get-go.

Heresy! Yeah, but I been doing this for about a year. I did side-by-side experiments, early on. I observed no difference; subjective observation to be sure, but no difference. 

My baking goals, from the start, have been very modest and focused: Make flavorful, eye-appealing loaves to share with friends and family. And K.I.S.S. (Keep It Simple, Stupid!) Eliminating the "add the salt, and incorporate into the dough after autolyse" step is in the spirit of the latter, and doesn't seem to observably degrade the first, and #1 priority, goal.

I found adding salt to hydrated dough difficult, and early-on, had the uneasy feeling that although it disappeared into the dough quickly, it wasn't well incorporated into the dough until much later into the fermentation.  I also thought, initially, "Wow, holding back 5% of the water, during the autolyse, and subsequently adding it to the dough with the salt dissolved in it (mostly) seems a good trick!" (Tartine Bread advocates will recognize this technique). But then, thinking further, I reasoned, "Holding back water during the step wherein the flour saturates (with water)? Huh?"

So shoot me.

Nico, I'd be grateful if you'd send me the reference(s) URL.

Thanks,

David G

 

nicodvb's picture
nicodvb

I'll post the link, but I have to say it will be complicated. Generally I don't collect the papers I find and going back the the search terms will require some effort:-)

Sorry, I know it's not a scientific approach but it's how things evolved.

Just to add to the heresy choir... yesterday I baked a panettone begun with a salted preferment (10 gr rye starter, 40 gr of water, 0.5 gr of salt and 50 gr high gluten flour). Well, it has a very nice dome:-)

nicodvb's picture
nicodvb

http://aem.asm.org/content/64/7/2616.full

 

In particular:

Sourdoughs usually are prepared without the addition of salt; nevertheless, several processes that make use of the incorporation of 2 to 5% NaCl in the sourdough have been developed (30). Our data are consistent with the observations of Röcken et al. (22) and Gianotti et al. (9) that increasing dough yields leads to faster acidification of doughs. The addition of salt may alter the composition of the microflora, because C. milleri is much less sensitive to salt than the strains ofL. sanfranciscensis. Yeast growth in dough may even be stimulated by the addition of NaCl. In agreement with this assumption, it was observed that the addition of NaCl to wheat doughs inhibited the growth of lactic acid bacteria while it exerted a stimulating effect on yeast (9). We expressed the salt concentration as ionic strength rather than water activity. This was considered justified on the basis of the results of Dossmann (7), who observed a more pronounced growth inhibition of Lactobacillus sakei if NaCl replaced glycerol for adjusting the water activity to values ranging from 0.92 to 0.99.

 

 

 

 

The former reported study is

  1. Gianotti A.,
  2. Vannini L.,
  3. Gobbetti M.,
  4. Corsetti A.,
  5. Gardini F.,
  6. Guerzoni M. E.
(1997) Modelling of the activity of selected starters during sourdough fermentation. Food Microbiol. 14:327–337.
Hope it helps!
Breadandwine's picture
Breadandwine

I've always added salt right from the beginning - in with the flour. Well, it's what my baker dad did, so I thought nothing of it. I do find it slightly annoying when recipes make a big deal out of separating salt and yeast - even when both are in a dry state as in adding ingredients in a breadmaker.

About adding sugar: ever since I read that beating sugar with fresh yeast - which used to be a common instruction in older recipes here in Britain - will (can) result in the death of the yeast, I've avoided that technique (not sure I ever used it, anyway). I say can, because if lukewarm water is added straight away, you can probably get away with it. I've never noticed that increasing sugar in a dough will result in a slower rising, but I'll look out for it from now on.

Oil I've never had a problem with (I'm a vegan, having given up animal fats about 10 years or so ago). The first bread I ever made with a significant amount of oil in it was a ciabatta - and these always rise very well indeed. I've found that olive oil is the best oil to use in bread - except when it comes to pizzas where the oil (mostly sunflower oil) from a jar of sun-dried tomatoes gives an almost short-crust texture to the crust.

(As an aside, it was seeing how well ciabattas rose that alerted me to the fact that the more water you use in a dough, the better it rises. Previously I'd been under the impression that the more water you added, the heavier the bread would be - makes sense, doesn't it?)

I suppose there must be a limit to the amount of fat a dough will tolerate - but I haven't found it yet.

Now alcohol - that's a whole different ball-game, as this chastening tale will testify:

http://nobreadisanisland.blogspot.com/2011/09/celebration-birthday-loaves.html

For those who haven't time to go through the whole, sorry saga, here it is in a nutshell:

I was making a couple of celebration loaves for the birthday of some friends of mine (twins). I soaked 200g of dried unsulphured apricots in Benedictine for a couple of weeks, then used the soaking liquid in the dough - and then kneaded the apricots into the dough instead of gently folding them in. The yeast quite naturally gave up the ghost and it took me several attempts to rescue the bread. I managed it in the end - took me a couple of days, but they turned out fine. 

I'm happy to report the loaves received rave reviews - with one of the recipients asking for the recipe.

Next time I'll just drink the soaking liquid - and fold in the apricots gently! :(

Cheers, Paul