Yeast life cycle

[doronin]

How many degassing cycles a plain bread dough can normally tolerate in room temperature? (instant or active dry yeasts)

My understanding is that yeast grows stops when it consumes all the available sugars. After how much time may it be expected, considering the dough is being degassed and folded/turned from time to time?

Edited December 25, 2005 by doronin (log)

[scott123]

With the starch and the starch converting enzymes present in dough, there is almost an unlimited supply of nutrients for yeast. As long as you are making additional sugars available to the yeast by punching down/redistributing the yeast throughout the dough, the yeast will continue to survive. I'm guessing you could probably do this for days. Eventually, though, the excreted alcohol will create an unhospitable enough environment to curtail yeast activity severely. As the dough ferments, yeast activity drops and the rising time lengthens.

I'm sure you've noticed that the initial dough doubling time is significantly longer than ensuing rises. This is the increasing yeast activity. Ideally, you want to bake the bread when the yeast activity is at it's peak. Once it hits it's peak (and this amount of time will be different for every dough) the doubling time will increase rather than decrease. If you plotted yeast activity on a graph, it would look like a hill.

Besides creating an inhospitable environment for the yeast and impairing them from doing their jobs, the alcohol created by excessively numerous degassing cycles will include potentially bad tasting by-products. Fermentation itself is not a bad thing. It's when you overferment a dough that you are asking for trouble.

I've seen different recommendations by different authorities about the number of times to let a dough rise. Two seems to be pretty popular. Amy (from Amy's Breads) recommends three or maybe even four. I take a different tack. I'm an adherent of the long cool rise. That's a slightly different ball game. Cold (retardation) will slow down yeast activity/alcohol production and, imo, allow the taste of the wheat to shine more brightly. Another reason why I utilize the long cool rise is that it's the technique my local pizzeria goes with. Replicating their bread (crust) is my ultimate goal.

[jsolomon]

In a rich media, which I would say that most bread dough is, you can expect the yeast Saccharomyces cerevisiae to have a fairly constant doubling time for about 24 hours if you keep the temperature around 30C.

So, divide 24 hours by how many hours (or fractions) between degassing cycles, and you'll have your rough answer.

[doronin]

First, thanks!

What are possible reasons that can stop/slow down yeast activity within 2-3 hours?

I question myself how can I know that it actually stopped - I don't, but the dough refuse to rise after the second degassing.

The room temperature I referred to is about 23-25C.

[jsolomon]

How much salt does your dough call for?

How is the quality of your water?

[doronin]

How much salt does your dough call for?

Nothing unusual, I don't remember the exact percentage right now, but I used to take it from the good books, such us Bread Baker's Apprentice, and such.

How is the quality of your water?

←

That's a good question. I used filtered tap water, and water where I live is more hard than soft. Hmm... Do you think this could be the reason?..

Another interesting thing is that the dynamics I described depend very little on amount of yeast I used. I use instant yeast, and on 800g flour I tried to add between ~3/4 to ~2 teaspoons of instant yeast, which resulted in very close low loafs. Timing varied, but insignificantly.

Edited December 28, 2005 by doronin (log)

[jsolomon]

It could be. Try using buttermilk or milk instead of water for one batch and see how that batch turns out.

[scott123]

It's a known issue with instant yeast:

http://www.baking911.com/Asksarah/_disc4/000029cd.htm

http://www.baking911.com/asksarah_oldsite/...c4/000029d1.htm

Switch to regular yeast and you should be fine.

[doronin]

jsolomon, thanks, I'll try and report here.

It's a known issue with instant yeast:

http://www.baking911.com/Asksarah/_disc4/000029cd.htm

http://www.baking911.com/asksarah_oldsite/...c4/000029d1.htm

Switch to regular yeast and you should be fine.

←

This is kinda strange... All "official" sources say that instant yeast is exactly the same culture, just "packaging" differs, and as a result - activation conditions: active dry has to be dissolved; instant goes directly into flour, but water is recommended to be warmer (the last I don't really follow). Proportions are also different as concentration of instant yeast is about 3 times higher then active dry. As for the rest there should be no difference...

[jsolomon]

I just had one more thought. Try adding a crushed vitamin C tablet to your bread. That might help.

As for numbers, etc, remember yeasts are one-celled organisms. They are [vaguely] simple and exist in large numbers for two reasons: they breed a gazillion times faster than rabbits, and if you look at them cross-eyed, they die.

To wit, in some of the research I'm doing, we had to do a freeze-thaw study on yeast, when we did it, we found roughly one in ten cells survived--and that was being nice to them, keeping them wet and coddled with glycerin.

The yeasts you've got are mostly sporulated for long-term storage which is a much rougher process. So, I wouldn't expect quite as high of a return on those.

[slkinsey]

A little diastatic malt powder in the dough should also make a difference.

[doronin]

Yeah, I know about ascorbic acid and diastatic malt. Byond the fact I have no way to get them where I live, I guess they affect the dough, usually positively, but my quest now is to find what damages yeast activity.

I remember words of grandma of someone that some her yeast doughs do have trouble to tolerate more then one-two risings, she didn't know why of course.

I still hope somebody in eGullet may have an idea what may cause yeast dough to be able to tolerate just one-two risings???

[danlepard]

Hello Doronin,

What quantity of yeast are you using to weight of flour?

And what temperature (roughly - warm or cold) is the water when you start mixing?

Are there any other ingredients in your mix like malt or sugar - I see you call it a plain dough, but some folks have different ideas about "plain"?

You use the word "degassing" and I wondered if that is exactly what you mean - does the dough rise up, then you push all of the air out of it, then this is repeated one more time?

Dan

edit to add more questions

Edited January 2, 2006 by danlepard (log)

[Anna N]

...

I still hope somebody in eGullet may have an idea what may cause yeast dough to be able to tolerate just one-two risings???

←

I have been struggling to find you an answer since you first posted this question as, in the back of my mind, I recall reading/hearing that instant yeast will not sustain multiple risings. However, despite a diligent search I cannot back up this fragment of knowledge. But if were trying to solve the problem for my self I would certainly switch from instant to traditional dry yeast. Wish I could be of more help.

[doronin]

Hi Dan,

What quantity of yeast are you using to weight of flour?

And what temperature (roughly - warm or cold) is the water when you start mixing?

I tried to play with it... As I don't have a scale with that level of precision, I have to measure the yeast in teaspoons. For 800 gr of flour I tried between 3/4 to 2 tsp of instant yeast, in total (meaning total of what was in preferment and the actual dough). Preferment gets pro rata amount of yeast (approximately), i.e. if my preferment made with 30% of flour by weight, it gets ~30% of yeast.

The temperature is usually cold, but again, after all the mix warms up it rises well, the first time.

Are there any other ingredients in your mix like malt or sugar - I see you call it a plain dough, but some folks have different ideas about "plain"?

Just filtered tap water, flour, yeast, and salt.

You use the word "degassing" and I wondered if that is exactly what you mean - does the dough rise up, then you push all of the air out of it, then this is repeated one more time?

I do "turns" by time, usually 50 min-1 hour, dough usually rises at least a little by then. I flatten it carefully, and do envelop fold. Then it goes back to rise again. I don't fully "degass" it.

Thanks,

Dmitry

[danlepard]

Right. I think what is happening is that your dough is exhausted. A combination of a commercially yeasted preferment and additional yeast added to the final mix means that you should be able to reduce the total amount of yeast used to a fraction of what straight dough needs.

Though I can't really talk for other bakers, when I'm folding the dough it occurs at intervals during the one-and-only rise before shaping, and it has the added benefit of speeding the fermentation by gently remixing yeast and unfermented matter. So I'm (a) only ever getting one rise out of the dough, (b) using very little yeast, and © the dough is still cool (21C - 23C) resilient and elastic before shaping.

The difference between 3/4 tsp and 2 tsp yeast is quite alot, and I can't really grasp the need to add more than the minimum necessary to achieve a slow gradual rise. Do measure accurately. Do try and get over the "I don't want to be precise but want to achieve excellence" attitude - I know what you're talking about as it used to be my mantra. You grandmother might have both claimed to be casual in her approach, and appeared to be when you watched her, but much like watching an experienced pianist her well-practiced ways simply made it "look" easy. Measuring a cup or a tsp wont take away from your enjoyment if they lead to a better result. Try something like this:

for the pre-ferment

250g bread flour

250ml warm water at 30C*

1 x 5ml tsp dry yeast

leave for 2 hours at 21C - 24C until the mixture bubbles up and just begins to drop back down

for the dough

300ml cold water at 18C - 20C

550g bread flour

2 x 5ml tsp salt

*both instant and easy blend yeast work best using warm water as it helps to break down the outer surface around the granules, and in turn allow the yeast to hydrate and begin fermentation quickly. It will happen still occur at lower temperatures (+4C upwards), but will need a much longer. Overnight in the refrigerator, with dry yeast, does produce very good dough.

Combine the prefement with the cold water then combine this with flour and salt. Leave for 10 - 20 minutes then lightly knead (I favour three very brief 10 minute kneads at 10 second intervals, but it's up to you). Gently stretch and fold the dough every 45 minutes until, when you cut into the dough you see a clear network of bubbles forming (2 hours maybe). And as soon as you get to that point divide and shape the dough for it's final rise. Don't try and give it any more folds. Shape and bake, as you prefer. This is the schedule I used for the bread below:

11.00am Mix pre-ferment

1.15pm mix dough

1.30pm first quick knead

1.40pm second quick knead

1.50pm third quick knead

2.45pm first fold

3.30pm second fold

4.15pm third fold

4.45pm divide, shape and in basket

6.45pm in oven

The point is try and reduce the amount of yeast you're using as I think you're seeing the effects of over-yeasting the dough rather than some failing in the fermentative power of the yeast you're using or a conflict with that yeast and other ingredients.

**edited to make corrections to kneading (10 seconds rather than 10 minutes x 3) and to add schedule and photographs

Let me know how you get on,

regards

Dan

Edited January 3, 2006 by danlepard (log)

[doronin]

Hi Dan,

First thanks for your advice. I'm a weekend baker, so hope to try it in a few days.

As for being presize - I'm trying, by measuring everything by weight. But yeast goes in so tiny amounts, so I'd need a special scale for that, which I just don't have.

The "dry yeast" you mentioned - my understanding if I go with instant yeast, and not "active dry" one, I have to take 1/3 of the amount in your recipe, right?

And, the last question, you don't add yeast to the dough, given that preferment at moment of mixing is in its most active state. But if I leave preferment overnight, most probably missing the peak moment, should I "refresh" it similar to sourdough, or add some additional yeast to the dough?

Thanks a lot

Dmitry

[danlepard]

Hi Dimitry,

I find the best way to measure very small amounts of yeast in is measuring teaspoons, the sort that come in a set on a ring. In the past I had editors (and readers) saying to me, "ah, but you're so keen on measuring water and flour by weight you must give the yeast by weight too". Like you, I find it difficult outside of a laboratory to measure 3.85g yeast. So I try to give spoon measures always. But they are measuring spoons rather than tea and coffee spoons.

I've been alternating dry and active dry yeast with identical measures and haven't found a big difference. The big difference between the two is the particle size and the way that affects the time needed to initiate fermentation. But there is no difference between the yeast strain used in the manufacture of both "dry" and "active dry". One of the large generic yeast manufacturers, DCL, recommend replacing "active dried yeast by up to 75% by weight of instant [fast acting] yeast, depending on the breadmaking processes employed and climatic conditions." I haven't found that 25% difference to be too critical and for ease have been using the same volume of each, testing it both ways to be sure.

Roughly every two hours, in a stable mixture, the yeast will multiply rather than set spores (an action yeast takes when the conditions suddenly change, like a big temperature drop). So I would say that after two hours you have the potential for more yeast to ferment in the fresh ingredients added when you mix the final dough. I don't think I would agree that the "preferment at moment of mixing is in its most active state". If you leave the mixture overnight at a constant temperature, what you'll be left with is a lot of yeast and no food for the cells to ferment as well as stray bacteria that would have multiplied in the mixture. The doughing, if you like, is the refreshment. Going back to your original question, the drop in activity partially reflects a drop in the amount of available fermentable material.

regards

Dan

[doronin]

Roughly every two hours, in a stable mixture, the yeast will multiply rather than set spores (an action yeast takes when the conditions suddenly change, like a big temperature drop). So I would say that after two hours you have the potential for more yeast to ferment in the fresh ingredients added when you mix the final dough. I don't think I would agree that the "preferment at moment of mixing is in its most active state". If you leave the mixture overnight at a constant temperature, what you'll be left with is a lot of yeast and no food for the cells to ferment as well as stray bacteria that would have multiplied in the mixture. The doughing, if you like, is the refreshment. Going back to your original question, the drop in activity partially reflects a drop in the amount of available fermentable material.

←

Dan, do I understand you correctly, you mean that leaving preferment overnight isn't a good practice as yeast left without food starts to produce alcohol and eventually dies? But overnight fermentation is usually recommended as a very convenient way to prolong fermentation to obtain better flavor?.. So, what's the right way to prolong fermentation?

[danlepard]

Sorry if I wasn't too clear - yes it is a good idea because you will have more yeast cells in the mixture by the end of the 12 hour (overnight) period. But the apparent lack of activity in the mixture doesn't mean they've all died - just that there is little left to ferment. When you scrape all of the mixture in with fresh flour and water to make the final dough you will find the mixture starts rising again. Yes, it is often good to leave the preferment overnight.

regards

Dan

[Anna N]

Sorry if I wasn't too clear - yes it is a good idea because you will have more yeast cells in the mixture by the end of the 12 hour (overnight) period. But the apparent lack of activity in the mixture doesn't mean they've all died - just that there is little left to ferment. When you scrape all of the mixture in with fresh flour and water to make the final dough you will find the mixture starts rising again. Yes, it is often good to leave the preferment overnight.

regards

Dan

←

Dan,

I would like to try this bread and have the pre-ferment in the 'fridge but I am curious if you really mean 3 very brief 10 minute kneads at 10 minute intervals? That's a total of 30 minutes kneading! Did you mean 10 seconds as in one of the recipes in your book? Thanks.

[jsolomon]

I still hope somebody in eGullet may have an idea what may cause yeast dough to be able to tolerate just one-two risings???

←

Cranky cooks?

I'm going to second the sponge method. You may have something in your water that the yeast don't like. I do. The sponge method sometimes works to get around that.

Sometimes it doesn't.

Did you try changing from water to milk or buttermilk?

[danlepard]

Yes Anna you're right (have just corrected the recipe). As I just quickly sketched out the recipe and, having no bread in the house, I though "I'll go and make it". Tasted so good, made with supermarket bread flour.

Doronin, try not double yeasting the dough and just rely on the pre-ferment. If it has only been left overnight there will still be a great deal of fermenting power in the mixture. Just extend the bulk fermentation of the final dough until, when you cut into the dough, you see a clear network of bubbles. Then shape as you prefer, let the dough double in volume and bake.

regards

Dan

[Anna N]

Yes Anna you're right (have just corrected the recipe). As I just quickly sketched out the recipe and, having no bread in the house, I though "I'll go and make it". Tasted so good, made with supermarket bread flour....

regards

Dan

←

Many thanks, Dan. I shall be waking it up in a couple of hours and will post my results.

[doronin]

Thanks for the picture, Dan!

Edited January 3, 2006 by doronin (log)