Author Topic: The Nature of the Yeast  (Read 10275 times)

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Offline gschwim

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The Nature of the Yeast
« on: August 25, 2006, 11:10:09 PM »
I recently read that to achieve a light, airy dough, one should cut down on the amount of yeast.  To me, this is counterintuitive as I had always thought that yeast's purpose was to make dough rise -- i.e., expand and that, to get the "puffiest" dough, I should use more yeast, not less.  Should I, instead, not use any yeast at all?

Also, any advice I can get on achieving a "puffy" (in the cornicone) and "airy" in the center crust in a 600% oven would be appreciated.

Gene


Offline varasano

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Re: The Nature of the Yeast
« Reply #1 on: August 25, 2006, 11:50:06 PM »
click the globe under my name to go to my web page, then search on the word 'intuitive' and I explain why it is in fact  counterintuitive but true

Offline Pete-zza

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Re: The Nature of the Yeast
« Reply #2 on: August 26, 2006, 12:00:42 AM »
Gene,

I'd be curious to know where you read that you should cut down on the amount of yeast to achieve a light, airy dough.

In my view, it is not the absolute amount of yeast that is important. It is how much yeast is left in the dough at the time of baking that matters. If you use a lot of yeast and let the dough rise for a few hours and bake it, you should get good oven spring and a puffy rim and crust. However, if you wait say, 3-4 days to bake the pizza, there may not be enough yeast left in the dough at that time to produce a good oven spring. As a result, the crust can be flat without much of a rim. I am assuming in both cases that no sugar was added to the dough and that the yeast was fed only sugars naturally extracted from the flour in the dough.

I have used as little as 1/5 teaspoon of IDY for a 16" pizza (about 21 ounces of dough) and achieved good oven spring and a good rim and crumb after a few days of cold fermentation. The yeast was fed slowly over the entire fermentation period by the sugars naturally present in the flour and there was enough yeast left in the dough at the time of baking to produce good oven spring. Reducing the yeast to zero as you propose would not produce acceptable results because no carbon dioxide can be produced without any fermentation. Without carbon dioxide, there cannot be any dough expansion.

What is also important is the temperature at which the pizza is baked and whether the pizza is baked on a hot stone/tiles, or on a pizza screen, or on a pan. Since the highest temperature that a pizza is likely to encounter in a conventional oven is on a hot pizza stone/tiles, that pizza will have the best oven spring of the three options. At the other end of the spectrum, all else being equal, a pizza baked on a cold pan will have the least oven spring of the three options. Of course, if there isn't enough yeast in the dough at the time of baking, none of the three options is likely to produce optimum results.

I don't know if you have seen this post, http://www.pizzamaking.com/forum/index.php/topic,3292.msg27915.html#msg27915, but it discusses some of the matters that you have raised. As for the specific question you have raised about the rim and center crust, I think the best way to achieve the results you desire is to use enough yeast in relation to the expected fermentation period (whether at room temperature or in the refrigerator), proof the dough skin after shaping to allow the dough to rise, and use a preheated pizza stone/tiles to bake the pizza. Starting with a reasonably thick dough skin and not overloading the pizza with toppings will also help.

Peter
« Last Edit: September 14, 2006, 08:52:08 PM by Pete-zza »

Offline varasano

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Re: The Nature of the Yeast
« Reply #3 on: August 26, 2006, 12:14:51 AM »
Pete, I've had 6 day cold rise doughs that had great spring. The key is not so much the amount of yeast you start with or the time it rises. The most important factors are:
1- how wet the dough is - the steam will blow up the bubbles started by the yeast. The wetter, the more steam, the more spring.
2- how well developed the gluten is - how tight are the bubbles - will they pop or hold when they are puffed up by the steam?
3- how much volume it has increased overall. If the dough has overrisen, the gluten you developed during mixing is weakened, like a bubble gum bubble past it's prime.  Overall, shoot for about 50% rise, not double in bulk, as many say. Obviously, the starting amount of yeast and the age of the dough can play into this number. The longer the rise, the less the starting yeast, to keep the bubbles down. I think that evelyne has posted the opposite of this, but I have to check with her to see what the thinking was there. The dough can rise by 50% in 2 hours or 6 days, depending on the starting amount of yeast and the temperature. But in the end the final size will be the big factor.

Jeff



Offline Pete-zza

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Re: The Nature of the Yeast
« Reply #4 on: August 26, 2006, 10:14:45 AM »
Jeff,

I think that you and I are saying the same thing, except that I tackled Gene's question from the standpoint of the yeast and you tackled it from the perspective of the hydration and the "strength" of the gluten network. But yeast, hydration and gluten development all work together.

The hydration, or degree of "wetness" of the dough, does allow for better openness and airiness of the crust and crumb, as was also noted by Tom Lehmann in the piece I referenced in my last post. A low hydration dough will be closed and tough and simply will not open up as much as one that is more highly hydrated. The development of the gluten network is also important because of its capacity to hold the gases of fermentation better and retain them longer. That is one of the reasons why high-gluten flours are often recommended. Their high-gluten levels translate into a more developed gluten network with an increased capacity to hold the gases of fermentation better and longer. But, it is not the flour alone. The way the dough is made will also be a factor. My simple KitchenAid mixer will not do as good a job as your DLX in developing the gluten, so I may not get as good an oven spring as you will, even disregarding for the moment that I am using a standard home oven and you are using much higher oven temperatures that contribute to greater oven spring. Your DLX will do a better job than my machine with just about any flour, just as a commercial Hobart mixer is likely to do a better job than your DLX.

The yeast level is important, especially at the time of baking, because even though you may have the ideal hydration and the optimum gluten network development, you will not get good oven spring without there being adequate yeast at the time of bake. By definition, oven spring is that event by which the yeast gives up its life as that final burst of fermentation occurs when the dough hits a very hot surface, like a pizza stone. Once the internal dough temperature gets to around 145 degrees F, that's it for the yeast and the dough won't rise anymore. At about the same time, at around 140 degrees F, the starches start to gelatinize, and at around 153 degrees F, they are completely gelatinized but still swelling. Without the right amount of yeast at the time of baking, none of this will matter. There may be some steam bubbles but less than optimum oven spring. As you noted in your point 3, what is also important is to take note of the condition of the dough just prior to baking. If the dough has expanded too much and too quickly and starts to collapse and fall back upon itself, this is a clear sign that the dough has overfermented, that is, the yeast has run out of food, and is heading south fast. The oven spring at this point may be severely compromised.

Jeff, if I understood your comment about the yeast quantity and age of the dough correctly, I think Evelyne would agree with what you said. If I am thinking about the right subject, I believe what Evelyne said was that, rather than adding sugar to a dough formulation to serve as food for the yeast over the fermentation period, she preferred to leave out the sugar and increase the amount of yeast instead.

Peter

Offline varasano

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Re: The Nature of the Yeast
« Reply #5 on: August 26, 2006, 11:32:11 AM »
Hey Peter,

I think we are mostly on the same page, but not exactly. I don't have time to write much detail. But I will say that a dough has passed it's optimum rise well before it starts to collapse and well before it has run out of food. A dough at 50% rise has plenty of food left to get it to a 100% rise. A 50% risen dough is not collapsing, but still rising towards 100%. But doing so is not good for it's final oven spring, because the walls of the bubbles will thin out and weaken and when the final steam push comes, they may hold now, but won't later when it counts.

I don't believe that the yeast is doing much fermentation in the final minute of it's life. I don't think there is a burst of fermentation. Rather, the expansion is due to simple heat expansion of the gases which have previously started to form and be captured in the gluten bubbles, plus additional water vapor.

Assuming a start temp of 75F and and end temp of 175F, the expansion of the gas due to heat can only account for an 18% increase is pressure Measured using the absolute or 'Kelvin' Scale these temps are 297K & 352K which is an 18% rise and corresponds directly into an 18% increase in pressure and volume.  However, given the same rise in temp the water vapor pressure rises from 22 mmHg to about  350 mmHg - a 1500% increase. This does not translate into a direct increase in volume, the way the straight gas expansion does, because only a portion of the gas is water vapor, but still only a small amount of water changing to vapor, can dramatically increase the internal pressure and cause the dough to rise.
« Last Edit: August 26, 2006, 11:36:01 AM by varasano »

Offline Pete-zza

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Re: The Nature of the Yeast
« Reply #6 on: August 26, 2006, 12:16:09 PM »
I don't believe that the yeast is doing much fermentation in the final minute of it's life. I don't think there is a burst of fermentation. Rather, the expansion is due to simple heat expansion of the gases which have previously started to form and be captured in the gluten bubbles, plus additional water vapor.

Jeff,

Maybe you are right but I was using the expression “oven spring” in the sense that it is often described in the literature and as I researched it some time ago when I was working on the Pizza Glossary for the forum. For example,

When the loaf is first placed in a well-preheated and hot oven, the heat from it causes a final burst of fermentation and expansion called "oven spring". This gives the bread a nice rounded and well-risen top.Oven spring continues through the first five to ten minutes of baking and stops when the loaf has reached 140 degrees F when the yeast dies. The flour's starches gelatinize and the gluten sets, making the loaf's shape permanent. (baking 911.com);

and

oven spring: The rapid increase in the volume of a bread (in this case, pizza crust) during the first few minutes of baking. It occurs when the yeast hits a hot oven and gives its last gasp, puffing up the crust. (sliceny.com Glossary)

and

When shaped dough is placed in an oven, it is surrounded by both top heat – the hot air on the top and sides of the loaf – and bottom heat, from the baking stone or tiles underneath. This heat causes the yeast, in the last gasp of its life, to lift the dough one more time: the process called oven spring. (Nancy Silverton, Breads from the LaBrea Bakery).

Peter



Offline varasano

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Re: The Nature of the Yeast
« Reply #7 on: August 26, 2006, 12:53:13 PM »
Boy, I'd love to see the scientific proof for that.  I think this is a Mythbusters moment.

Yeast activity just doesn't account for the observations.  Didn't pftaylor clock a springy pie at 42 seconds in a recent post? Organic processes just don't work that fast. These are physical changes due to heat. I do believe that the rise might stop at a certain temperature due to physical changes in the starch, but not due to the death of the yeast or to increased fermentation.  For a large slow cooked loaf of bread, maybe the warming of the interior causes a speeding of the rate of fermentation. But even at a faster rate, it's not going to amount to much for these fast pies. So given the excellent spring of these super fast pies, it can't explain the spring. Another explanation is needed.

As far as the multiple accounts go, what often happens is that one definition gets repeated over and over. For example, if sliceNY used the term 'last gasp' and so did Nancy, this is not likely a coincidence. It's like when Dick Cheney was picked as Bush's running mate and 40 reporters in a week said, "Cheney adds, a certain depth - what's a good term? - a certain 'gravitas', to the ticket." Like they all just thought of 'gravitas' themselves.  I'm sure to bakers who made bread in 20 minutes, someone came up with this explaination, it sounded logical and it gets repeated until it's common knowledge. It fit their observations. If yeast at  85 could double a dough in an hour, then at 120 it could double in 15 minutes. So it's a plausable explanation.  But given a 42 second pie with great spring, it can't be the explanation.  It doesn't fit the data, the new observation. This is how knowledge progresses...

That's why these mythbuster guys are in their 3rd season.

Jeff
« Last Edit: August 26, 2006, 12:58:54 PM by varasano »

Offline David

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Re: The Nature of the Yeast
« Reply #8 on: August 26, 2006, 01:36:40 PM »
Funnily enough i have noticed that if i place a pizza in my oven at around 550,i get an initial spring,but it also seems to get a second rise a little later at the point just prior to coloration forming.Am I imagining this or just too inebriated?When a pizza is placed in the oven at approx. 850,I get one fast spring,equal or greater to that of a cooler oven ???
                                                                                      David
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Offline Pete-zza

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Re: The Nature of the Yeast
« Reply #9 on: August 26, 2006, 01:53:43 PM »
Jeff, I know what you mean about the repetitiveness. I do a lot of online research and I find things repeated all over the place, including stuff from our forum. The people who do it often pass off what they post as their own.

I didn't want to use my own "oven spring" definition (the one in the forum Pizza Glossary) as authority for the point I was trying to make, but when I went to the Glossary, I thought it was pretty accurate. I did a fair amount of research when I wrote the definition and I tried to be careful in my choice of words. As you will see here, it is broader than the earlier definitions I quoted, perhaps because I knew that steam is also produced in addition to fermentation:

OVEN SPRING: The rapid increase and final burst in the expansion of dough once it is loaded into the oven. The dough expansion will cease as soon as the temperature of the dough reaches about 140° F, at which point the yeast dies. There are many factors that influence the degree and quality of the oven spring when baking pizzas, including overall dough quality (it should not be stiff or overkneaded, and it should have good hydration), the amount of yeast in the dough as of the time of baking, the degree of fermentation (it should not be underfermented or overfermented), and oven temperature. The manner in which the pizza is baked, that is, whether using a pan, stone/tiles, or pizza screen, will also be a factor.

David, I can't say for sure but I think that the second increase you observed may have been the swelling of the gelatinized starches.

Peter



Offline varasano

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Re: The Nature of the Yeast
« Reply #10 on: August 26, 2006, 02:55:42 PM »
I would still separate the two factors. That definition is more clear, but still overly links the expansion to the yeast, in my opinion.

There's another issue. Mabye there is a different term. When I refer to the dough being springy, I'm not just referring to oven expansion. I'm referring to how the dough reacts after it cools. I've seen dough spring a lot in the oven, stay there too long, dry out, fall and/or become hard. Technically, the original spring was the same. But the quality of it being springy later on is different. To me, it is the final springyness that counts. Therefore I don't really use the term 'oven spring' because I'm really referring to the spring of the final product. 

Jeff




Offline charbo

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Re: The Nature of the Yeast
« Reply #11 on: October 04, 2006, 07:59:34 PM »
I was just checking artisan.net and was reminded of some basic physics.  CO2 dissolves readily in water.  The colder the water, the more gas dissolves.  If yeast-generated CO2 reaches anywhere near the saturation level in the water of a dough, a rise in the temperature of the dough will generate a lot of gas coming out of solution and a relatively huge volume expansion.  A wetter dough will have more dissolved CO2. This explanation corresponds with the observation that wetter doughs yield more puff.

cb

Offline Pete-zza

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Re: The Nature of the Yeast
« Reply #12 on: October 04, 2006, 08:49:55 PM »
The explanation I recently read at the San Francisco Baking Institute is as follows:

During...the baking time, the yeast and enzyme activity are stimulated by the quick increase in temperature. Because more sugar is transformed by the enzymes, and because of the faster yeast metabolism (due to higher temperature), a large amount of carbon dioxide is produced and retained by the gluten structure, developing the volume of the bread. This is what we generally refer to as the "oven kick" or "oven spring". Bakers should remember this intense gas production when evaluating the end of the final proof; gluten must be able to retain more gas when the dough goes into the oven.

When the temperature inside the dough reaches 122 degrees F, the starch granules start to swell and the yeast starts to reach a dying stage.

At 140 degrees F, the starch begins to gelatinize. Under the effects of heat, the starch granules burst and liberate many chains of starch which form a very complex, gelatin-like matrix that will, after cooling, create the crumb of the bread.

At 145 degrees F, all yeast activity ends, as the cells of yeast have been killed by the heat. However, the bread is still increasing in volume. The gas produced by the yeast starts to expand.

At 153 degrees F, starch gelatinization is complete. At 165 degrees F, the gluten starts to coagulate and the chains of protein start to solidify. At this point, the structure of the bread is completely set.

At 180 degrees F, all enzyme activity is over and no more chemical transformations occur in the dough.


Peter
« Last Edit: October 05, 2006, 08:37:11 AM by Pete-zza »

Offline shango

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Re: The Nature of the Yeast
« Reply #13 on: October 04, 2006, 10:15:25 PM »
Properly proofed dough, preferably risen once at room temp until roughly doubled in size, risen again under refrigeration until just about doubled again ( should have some air bubles on the surface), scaled and rolled into balls, back into the refrigerator for about 8 hours or so (or until big, soft and poofy), back out to room temp until the dough itself reaches room temp and is really starting to poof on it's own.  Then stretch the dough and top it.

Now the most important part.  Immediatly fire the pizza into a very hot (over 750 degree) oven.

The oven should have a ton of actual FLAME (not coals).  The flame should ideally be licking across the entire top of the oven. 

Now watch that cornicone blow up.  If it takes less than 2 minutes to cook the pizza completely you did it right.

enjoy,
-E
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Offline Pete-zza

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Re: The Nature of the Yeast
« Reply #14 on: October 04, 2006, 10:39:12 PM »
Edan,

How much fresh yeast, however you measure it, is needed to allow the dough to perform as you described?

As I understand it, in Naples it is not common to refrigerate dough for fermentation purposes, and that essentially only room temperature fermentation is used. Is there a reason other than a business reason (e.g., a dough inventory/management reason) for using the cold fermentation?

Peter
« Last Edit: October 04, 2006, 10:44:30 PM by Pete-zza »

Offline shango

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Re: The Nature of the Yeast
« Reply #15 on: October 04, 2006, 11:51:03 PM »
Without getting to complicated the amount of yeast used depends on a lot of factors, the major ones being ambient temperature, water temperature and humidity. In hotter more humid weather you will need less yeast to get the rise started, in cold weather a little more yeast is necessary.

Now, what most people don't understand is that once the yeast starts to consume the sugars in the flour it begins to reproduce (create more yeast).
so, only enough yeast to start the fermentation is necessary after that it takes care of itself.  It is better to use less, as a large ratio of yeast to flour will cause the dough to rise to quickly and it will become a sticky yeasty smelling mess that it hard to stretch and does nothing in the oven.

I find that about a 1/4# of fresh yeast to 50# of flour is about right.

The purpose of the refrigerated rise is to allow the dough to form glutens (elasticity) for a good stretch and a nice smooth texture.  It also allows the dough to develop a softer mouth feel and a better flavor.

I believe that the double rise is also required in order to maintain the DOC status....I am not 100% sure that the second rise is required to be done under refrigeration though...(I will look into it.  It has been some time since I have read the rules)  I can tell you that in an emergency the dough can be rushed from the freshly rolled ball stage to pizza without refrigeration with very good results.  I would never skip the initial room temp rise and the secondary rise under refrigeration though,  This would make the dough tough, grainy and very difficult to work with.

-E

pizza, pizza, pizza

Offline November

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Re: The Nature of the Yeast
« Reply #16 on: October 05, 2006, 12:01:50 AM »
I'm going to have to agree more with varasano on this one.  Grizzly bears will learn to read the Wall Street Journal before yeast begins to have that much to do with a rise in the oven.  At 0.0344 psi/min/g, the only thing yeast is doing in the final minutes of its life is creating more voids for the steam to stretch out.  The volume of CO2 actually produced by the yeast is miniscule and if it were not for a very hot oven, the crust would barely rise at all.  If you want, you can take a hairdryer on its highest setting to your dough sometime and see for yourself.  A hairdryer should produce at least 130 F at the surface, which would be enough to stimulate the yeast into producing the greatest amount of CO2 possible.  Compare that with the crusts you pull out of the oven for the same amount of time.
« Last Edit: October 05, 2006, 12:05:18 AM by November »

Offline shango

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Re: The Nature of the Yeast
« Reply #17 on: October 05, 2006, 12:26:49 AM »
aha!  A very good point.  The yeast I'm sure does very little in the last minute of it's life, BUT,  It is absolutely essential that the yeast is still alive when it hits the oven.  Ever try to make a pizza with over risen dough?  It does not rise one bit..

and where does the actual air content of the dough ball come into play?  I have seen many a good pizza ruined by what I like to call "hammer hands"

How much of the dough stretchers faults do you want to blame on the yeast?

pizza, pizza, pizza

Offline November

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Re: The Nature of the Yeast
« Reply #18 on: October 05, 2006, 01:04:42 AM »
charbo,

I almost missed your post stuck in between all the others.  To address your hypothesis, the answer is basically no.  Carbon dioxide on its best day, under absolute ideal conditions will only dissolve into distilled water at about 0.0411 g/oz of water.  So if your single pizza contains 6 oz of water, and it doesn't have anything else dissolved in it like yeast, sugar, flour (you get the idea) and the temperature is 77 F, the amount of CO2 that can be dissolved in your pizza is about 0.2466 g/6 oz of water.  This equates to 124.566 cc of undissolved CO2, or 4.9942 cm cubed if you prefer.  That's not enough gas to lift much of the crust even if it were under ideal conditions.  The bottom line is that there are too many dissolved solids already in the water for CO2 to dissolve as well.
« Last Edit: October 05, 2006, 01:52:16 AM by November »

Offline November

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Re: The Nature of the Yeast
« Reply #19 on: October 05, 2006, 01:19:13 AM »
shango,

It is absolutely essential that the yeast is still alive when it hits the oven.  Ever try to make a pizza with over risen dough?

Uh, no it isn't essential.  Ever made biscuits?  Even if you wait until the chemical reaction between the leavening agents is complete before putting the dough in the oven, you will still get a substantial rise.  The reason a dough you refer to as "over risen" doesn't rise much is because the gluten structure eventually dissolves in the alcohol that the yeast produces.  In some cases, it's also because the water is consumed by all the yeast or dehydrated from the mass altogether.