Salt stressed yeast for sweet breads

[jackal10]

I often have trouble getting very sweet doughs to rise, even with osmo tolerant yeast.

According to http://www3.interscience.wiley.com/journal/122610047/abstract?CRETRY=1&SRETRY=0 stressing the yeast by soaking for 40 minutes in a 7% salt solution gives improved performance for sweet breads.

As people are coming to tea, I though I would try - this formula is adapted from the experimental one in the paper by adding sultanas. I also used a different flour.

It seemed to work well, alough I should have done a control. This is a very sweet bread, almost cake, with 24% (yes 24%) sugar

1. Rehydrate the yeast

Yeast 2% 4g

Water 0.5% 1g

Sugar 0.5% 1g

FLour 0.5% 1g

Mix together and leave for 5 mins

2. Salt stress

All the above

Salt 1.5% 3g

Water 17% 34g

Leave for 40 mins at 25C

3. Main dough

Flour 99.5% 199g (I used white spelt from http://www.glebe-flour.co.uk/ The dough was a bit slack so I added anther 100g)

Milk powder 4% 8g

Sugar 23.5% 47g (!)

water 43% 86g

Butter 4% 8g

Sultanas 50% 100g

Mix on high speed. Shape and pan. Proof in high humidity 30C (orgiginal forla said 38C)

Egg wash and bake at 200C for 40 mins (I used 220C for 15 mins and 190C for 25 mins) Sweet breads bur easily..

Edited October 16, 2009 by jackal10 (log)

[Kerry Beal]

Very interesting. Will you try the control loaf next to determine the difference?

[dougal]

Folks might have better luck with this link to the abstract

http://www3.interscience.wiley.com/journal/122610047/abstract?

Baker's yeast was stressed in 7% salt solution then mixed into dough, which was then evaluated for fermentation time, dough fermentation producing gas, dough expansion, bread specific volumes, and sensory and physical properties. The results of this study indicated that salt-stressed Baker's yeast shortened fermentation time in 16% and 24% sugar dough.

I note that the abstract doesn't talk about getting the yeast to rise at all with so much sugar around, but getting it to rise faster.

What specific "Bakers Yeast" preparation was being used? Compressed, actively dried or instant-mix? (Not cream because of the hydration step.)

My presumption would be that during the 'stressing' they are hoping to selectively grow the more osmo-tolerant cells before introducing the main dough. If yeast multiplication is indeed involved, oxygenation (even whipping) should help increase the rate. But wouldn't the cell osmosis conditions be as easily (or maybe better) manipulated (to select by stressing) with a sugar, rather than salt, solution?

And isn't an osmo-tolerant yeast simply a strain that has been pre-selected to better withstand the different cell osmosis conditions when (typically) strong sugar solutions are involved?

What mechanism do the paper's authors suggest might account for their findings?

[jackal10]

I used instant mix ("fermipan" type) HOVIS Fast Action brand.

The paper claims a 2.8x concentration increase of glycerol in the salt stressed yeast compared to the control, and quotes Hirasawa and Yokoigawa 2001 "Leavening ability of Bakers yeast exposed to hyperosmotic mediaq" FEMS Microbiol Lett 286:13-7 that suggests "a high correlation between intracellular glycerol accumulation and fermentation ability [in high sucrose concentrations]

[artisanbaker]

http://www.foodnavigator.com/Science-Nutrition/Salt-stressed-yeast-leads-to-bigger-softer-bread-Study/?c=zAc5rMw%2BSS6n5mlaYV5JaQ%3D%3D&utm_source=newsletter_daily&utm_medium=email&utm_campaign=Newsletter%2BDaily

Here is the link that I was originally tweeted by a UK bakery organisation called Real Bread.

(please let me know after you have all reached your conclusions; I'm going to keep going the "old" way until enough conclusions have been made!

[dougal]

I used instant mix ("fermipan" type) HOVIS Fast Action brand.

The paper ... quotes Hirasawa and Yokoigawa 2001 ... "a high correlation between intracellular glycerol accumulation and fermentation ability [in high sucrose concentrations]

Four points.

1/ UK Hovis-branded instant-mix is actually a bread machine product. Its loaded with a cocktail of "improvers" (or was, the last time I checked the small print 'ingredients' listing.) IMHO that's really not ideal as a basis for generalisation. And "rehydrating" instant-mix products outside a dough mix is not an assured means of getting lots of live yeast - as a control, I'd suggest that an instant mix yeast be used in an instant mix!

What yeast preparation did the research authors use?

2/ Wouldn't "intracellular glycerol" be a mechanism for ordinary 'osmo-tolerance'? Surely some of these folk have looked to see HOW regular osmo-tolerant yeasts function?

And have they compared their stressed yeast to commercial osmo-tolerant products? Isn't that the real question?

http://www.foodnavigator.com/Science-Nutrition/Salt-stressed-yeast-leads-to-bigger-softer-bread-Study/?c=zAc5rMw%2BSS6n5mlaYV5JaQ%3D%3D&utm_source=newsletter_daily&utm_medium=email&utm_campaign=Newsletter%2BDaily {ADDED - this is Artisanbaker's link}

3/ This journalist, and his headline-writer, seems to have generalised this to ALL bread, rather than just (very) sweet breads.

Salt-stressed yeast leads to bigger, softer bread: Study

By Stephen Daniells, 29-Sep-2009

Exposing Baker’s yeast to a salt solution prior to bread baking can improve the volume, texture, taste, and aroma of the finished product, says a new study.

According to results published in the Journal of Food Science, bread baked with the salt-stressed yeast (Saccharomyces cerevisiae) reduced the time for fermentation by about 25 per cent, as well as improving the overall sensory properties.

The results indicate that all the major parameters of the finished bread were improved in the salt-stressed bread, offering opportunities for bread makers.

You'd never guess that the study referred to sweetened breads ... and did not compare against an osmo-tolerant control.

I suspect that already there may be people on this wonderful internet claiming how superior this method is for recipes that involve no added sugar whatsoever.

4/ Lubricant?

Increases in volume may be due to “glycerol acting as a lubricant for the gas bubbles, allowing greater expansion”, suggested the Taiwanese and Rutger researchers.

A lubricant for the bubbles?

Really?

And this Glycerol is INSIDE the yeast cells, and it is 'lubricating' bubbles that are where?

How might 'lubrication' of bubbles allow greater dough expansion? Where's Boyle's Law?

Sadly, that comment makes me highly sceptical of their interpretation.

Yes, I can accept that Glycerol inside the yeast cells ("intracellular") would help to reduce the osmotic pressure (difference) across the cell membrane, which in a salty or sugary solution leads to the yeast cells losing water (drying out) and hence becoming less 'functional'.

A tiny total amount of Glycerol - in precisely the right place, right inside the yeast cells - does have the potential to change the functionality, the 'metabolic rate', of the yeast in difficult conditions.

Its hard to believe that tiny traces of Glycerol in the bulk of the dough, could possibly act as significantly on the physics of the bubbles, as it might on the biochemistry of the yeast cells.

Also, I strongly doubt that there's any specific connection between SALT specifically (as opposed to, say, sugar) and the expression of osmotically-balancing Glycerol.

Or that pre-stressing a 'standard' bakers' yeast strain is going to produce a better result than using a bakers' yeast strain that has been carefully selected and grown for its ability to retain functionality in a challengingly sugary environment.

While this research might have shed some light on part of the mechanism of osmo-tolerance (if that wasn't the result of the cited paper from 2001), I rather doubt that this particular pre-stressing method has much potential for making 'better' bread.

However, I'm a mere amateur ...

Edited October 21, 2009 by dougal (log)

[jackal10]

The original paper used "Instant Baker's yeast powder, produced specifically for bread making, purchased from Yung Chen Industry Ltd, Yaipei, Taiwan"

I guess they mean http://www.yungcheng.com/big/product_detail.php?id=97

My example was just a demo.

Edited October 21, 2009 by jackal10 (log)