The Physics of Stretch and Fold with a Video

The video on YouTube 'Strongest Dough Lightest Crumb' is a demonstration of making large volume light weight light crumb loaves in under two hours.  the science behind the video includes the 'outrageous' description of gluten as a mixture of two glues, one with a half life of less than 5 minutes, the use of pre-tensioning in dough to make it stronger, the ability to shape the foam bubbles to their least energy shapes, and the consequences.  The loaves in the video are the results.

 HOW TO MAKE THE STRONGEST DOUGH

In bread making the expression ‘strong dough’ is used to describe a dough that holds its shape  without having to put it in a tin or some sort of bowl.  There is also the assumption that this strong dough will produce an excellent rise.  The strong dough that I make easily meets these criteria.

The physics that explains how to produce a ‘strong dough’ is missing from both the amateur and professional bread making texts, as is obvious in numerous videos on YouTube.  The viewer is fobbed off with  descriptions involving gluten strands and their alignment etc.

The physics explanation is about the force produced by the  glue called gluten when it is pre-tensioned.  This is the force that makes the dough strong.   With two new handling techniques bread makers will be able to make bigger loaves in less time without the use of containers.  At this point I suggest you watch the YouTube video ‘Strongest Dough Lightest Crumb to see what this science stuff means in practice.  There is nothing else like it on the WWW, it shows a very straightforward routine for bread making.

The glue holding everything together in dough is actually two glues, one of which is elastic.  Elastic materials can be pre-tensioned, which is a way of saying they can be strengthened.  The whole mass of a piece of dough can be strengthened, not just the outside layers of a ball of dough.  Moreover the developing dough foam can be forced into its lowest energy state, which means the foam is less likely to go out of shape over a period of time.

The following simple explanation of how the glue works has enabled me to increase the volumes of my loaves, produce an excellent crumb quality, and cut the total loaf making time to under two hours.  Behind all that is the ability to produce a very strong dough.

 Stretch a newly kneaded piece of dough and it shrinks a bit when you let go.  Newly kneaded dough contains a mixture of two versions of the glue gluten.  One version is extensible, stretch it, let go and it stays stretched.  The other version is elastic, stretch it, let go and it shrinks back to its original size and shape.  Both glues are equally gluey.

Some extensible glue switches to elastic glue when there is relative movement between layers of the dough as in kneading/shaping.  An elastic glue can be pre tensioned to a strength way beyond what is needed to hold the shape of a piece of dough, with or without its developing dough foam.  Though the half life of the elastic glue is less than 5 minutes, it can exert enough force on the developing dough foam to shape the bubbles to their minimum energy states for the dough shape.  The elastic glue reverts to the extensible version in around 25 minutes,

The viscous nature of the films in the dough along with the inherently stable loaf shape allow the dough to develop to full loaf shape without the use of any container.  New dough handling techniques are required to make best use of the elastic glue as are new recipes.  The attachment ‘kendalroll’ gives the technical details of the handling techniques, recipes, etc.

A final thought, each bubble in the dough foam has a surface of the elastic glue since the bubble is growing.  When the growth stops I predict the bubbles will expand and the films of all the bubbles will get too thin and burst.



                                 The bread making world cannot see the glue for the strands

The structure, properties, and uses, of a Kendal Roll and Pulling Roll
 
Background
Dough can be pre-tensioned to such an extent that a piece of rising dough does not need a container.  To be suitable the dough must pass the window pane test, or form a ball  in a mechanical mixer. The amount of pre-tensioning available is far in excess of what is required to control the developing dough foam, a piece of dough can be made nearly rigid.  The Kendal Roll and Pulling Roll are the techniques that produce  pre-tensioning of dough.  I have not found anything  like them when searching the baking and scientific literature.  The techniques are particularly effective for producing large volume open crumb loaves from  a small amount of flour  in an ordinary oven.  Typically 300 - 400 g of flour produces a round loaf of base 8 to 11 inches and height 4 inches or more.  People handling such a loaf express surprise at its size and how light it is.  The density is around 0.2 g/ml.  The loaf mass is typically around 300 - 400 g for the smaller loaf.

The structures
A piece of Kendal Rolled dough looks sausage like. It appears to be made of a rectangular sheet of dough rolled from one corner of the sheet to the corner diagonally opposite.  In fact it has been produced from a stick of dough through a series of hand actions on the end of the  stick, the sequence of actions make up the  ‘Kendal roll’.  Each action produces a small strip of highly stretched dough, stretched both away from the end of the stick and at right angles to the stick.  This is glued to the surface of the previously stretched strips that together will make up the sheet.  The glueing action is to roll the already produced part of the roll onto the newly stretched strip, glueing it under tension to a surface already glued under tension. It is much easier to see it in action!
 
The increase in length of the new sausage is caused by the pulling apart of the dough at, and near, the centre of the newly forming sausage, this is the action that also stretches the dough sheet at right angles to the sheet and creates the sheet shape.  The result is not just a pre-tensioned sheet but a build up of pre-tensioning force in the already pre-tensioned body of the new sausage.  The baker can feel this effect taking place and must pull harder as the sausage length increases.  This effect leads to a sausage that the baker cannot stretch anymore.  This sounds crazy but try it for yourself.  The effect usually happens as you try to Kendal roll a piece of dough for the third consecutive time, one roll after another.

 The Kendal rolled dough sausage resists being stretched and resists being squeezed.  It is in a pre-tensioned state and returns to this lowest energy state  after deformation.  In other words it has become stronger.  

The Pulling Roll is a Kendal Roll without the sideways stretch that would produce the length of the sausage shape.  Instead a ‘catherine wheel’ shape results that has considerable structural strength, many small ‘pulls’ and ‘pins’ take place to produce it.  Turning the catherine wheel onto its side produces a strong cylinder, and over rising time, a round loaf.

The glueing
It is not possible to pre-tension dough unless there is an elastic glue in the dough.  Gluten behaves as two glues.  The ‘main’ glue is extensible, some of this is converted to an elastic glue when the shape of a piece of dough is changed.  This elastic glue has a half life of less than 5 minutes.  It has reverted to the extensible version in 25 minutes.  Both glues have the same glueiness.  The two glues exist together.
 When the elastic glue is present there is a minute stretchy force between the dough particles glued together.  This force enables the pre-tensioning to take place.  The dough mass is pre-tensioned by the manipulation.

There is another source of the elastic glue, the growing/developing foam bubbles which stretch the thin dough skins around them.  They get an elastic ‘skin’ over their surfaces made of the elastic glue.  This exerts a compression force on each bubble.   Once bubble growth stops the ‘skin’ starts to convert to the extensible glue.  There will be an increase in bubble volumes, a thinning of the gluten walls, the start of the dough foam collapse, perhaps?

There is also the effect of butter on the strength of the glue.  The strongest glue is produced without butter present in the dough.  With a mechanical mixer the butter can be added after the balling of the dough that has reached window pane standard.  It is added in flakes and takes perhaps two minutes of bread maker paddle action to become spread throughout the dough, the dough remains strong.

Work surface practice
There is so much dough handling that it is essential to use an oil film technique.  It is very simple.  There are two small work surfaces, I use two silicon mats.  One surface has an oil film brushed on it using the back of a hand.  The other is left dry.  My finger tips and thumbs are oiled.  Newly kneaded dough is placed on the oiled surface and pulled and rolled over it to get a log of dough covered in an oil film ready to be Kendal Rolled.  The log is lifted onto the dry surface and Kendal Rolled.  The new Kendal Rolled sausage is lifted back onto the oiled surface for the first rise.  It goes back onto the dry surface for the second Kendal Roll then is placed on the parchment paper on the tray for the final rise.  The aim is to keep to a minimum the amount of oil on the work surface.   On the dry work surface there is enough friction to carry out stretching and squashing without the log slipping or the squashed surfaces sticking too much to the work surface. On the oiled resting surface, along with the ease of oiling the log, the log does not stick to the surface during its rise.

There are two simple techniques to deal with the ends of a log of dough that is about to be Kendal Rolled.  The first is to thicken the start end by cutting an inch or so off and laying it on top of the new end to get a fatter end.  This avoids too tight an end roll that can spoil the foam.  The second is to squash flat the last inch of the far end of the log.  This ensures that the log end is firmly anchored to the log when it gets Kendal or Pulling rolled.

The properties of the Kendal rolled and Pulling rolled dough
The Kendal/Pulling rolled dough sausage has sufficient strength to control the shape of the dough foam for a few minutes.  In that time the foam bubbles that have been produced adjust their shapes to their least energy states in the new overall dough shape.  This is done in a viscous medium, it takes a minute or two to complete.  At any point in time the overall strength of the dough is the sum of the Kendal/Pulling rolled strength added to the strength of the elastic walled foam bubbles.

The Kendal rolled dough sausage is not necessarily the end product.  It can be left for 25 minutes then it can be rolled again to regain strength without an appreciable loss of gas.  If it is rolled again after another 25 minutes there is a noticeable gas loss but there is still more gas present in the new sausage than after two rolls.  

The cylindrical dough shape produced by the Pulling Roll is particularly strong.  The weak point is the flattened flap glued to the body of the cylinder.  As the dough foam expands this flap can overstretch and start to break up.  This is most likely to happen with low protein doughs.  The easy solution is put such dough in a tin.

Whether a long or round loaf, the shape is held better by making the loaf out of two pulling rolls not a single one.  Use the cutter along the first risen kendal roll to get two sausages, one about twice as fat as the other.  Move the thinner one onto the dry surface and pulling roll it.  Put the catherine wheel of dough back on the oiled surface.  Move the fatter sausage onto the dry surface, squash the far end and the near end.  Lift the catherine wheel and place it in its wheel position on the near end at right angles to the sausage length.  Lift the squashed end against the side of the wheel and start to do the pulling roll for the round loaf or a Kendal roll for the long tin loaf.

Simple properties of the dough foam are important.  As the bubbles grow the area of the base of the foam increases reducing the weight load on the bubbles in the foam making it easier to support the loaf shape.    Stretching the dough foam is ok, there is minimal bursting of bubbles.  When the Kendal or pulling roll is being carried out the newly forming sausage or catherine wheel is held slightly raised as it is rotated, removing the possibility of squashing bubbles which easily produces bursting.

 As already mentioned there is the slow change of foam bubbles’ shapes when dough is deformed.  The final round loaf dough is not inherently stable, if it is not stable it slips slowly over.  A slow hand push, followed by a minute or so of holding the hand in place, helps get the dough stabilized in the correct shape.  There is no such problem with a tin loaf.

The standard poke test to check when the dough is ready for baking does not work.  This is because the gas bubbles in the dough are much larger than ‘normal’, they are around their final lowest pressure state.

The ready to bake dough loaf is about as big as you would expect the baked one to be.  
The rising time is about 50 minutes, there is possibly a small rise in the oven or even a small fall.
Slashing the loaf surface does not work.  The whole dough loaf behaves as a block of jelly.

Log -a kneaded piece of dough that has been pulled into a log shape ready for rolling.
Sausage - a kendal rolled piece of dough

The flours

I use an all purpose enriched dough for all my bread.

The volume and crumb quality of malted/grain loaves are much improved over the standard flour packet recipes by working at a 70% hydration in my all purpose enriched dough recipe and if these flours are cut with strong white 50:50 then the hydration should be 75%.  The crumb is more open.

The yeast

At 5% the effects of the instant yeast are rapid I use a basic ‘spring’ bottled water.  I have used several of the yeasts available.  They have to be instant ones.

Bread making information

Protein range        10% up      plain flour and french flour upwards

Hydration               70% up      typical grain/malt plain, up to 90 + wholemeal
Flour load              300 g         gives a large round loaf 8-10 inch base 4 inch height.  One loaf                                                                        pushes normal bread knife length use. one 300 g round loaf  fills the
                                                baking tray. One 2 lb tin handles 300 g flour etc.

Yeast type                               instant fastest rise to fit with limited pre-tensioning time                                                                                   
Mix & knead                             Use a bread maker dough program or a mixer.           
                                                Pour hand warm water into pan and add the yeast and sugar then add flour                                                                         then salt.  Run the dough program.
                                               Add butter only after the ball of dough is well formed at window pane                                                                                   standard.               
                                           
Total rise time                         around 50 minutes

Baking             220 C             reduce to 190 C after 5 minutes then 30 minutes.                            
                                                       .       

Dough type        rich              6% butter    3% sugar/honey    2% salt        5 % yeast   No need to compensate                                                                   for honey or butter

Crumb                light soft      slight buttery honey flavour  added to natural flavours of flour

Crust                thin   crisp, cracks into tiles.   

Keeping quality    excellent

Advice                 first time make two loaves from 500 g,      one in a tin, one free.  They can go on the same                     tray like in video.               
                              You will want to put them in before 50 minutes, don’t.
                    They will be nearly fully risen going into the oven and a similar size coming out!   

Standard recipe for a Cumbrian loaf

Equipment needed
Bread maker/mixer for the kneading  I recommend a bread maker because of the fixed routine.
Two silicon work mats and oil for the film (I use rice bran oil)
A dough cutter
Basic oven tray with baking parchment or tins
Standard oven   


Recipe
300 g flour       I suggest a 50:50 mix of a strong  white and grain, average protein content around 13 %
225 g water     (75%) hydration
15 g yeast        (5%) two 7 g packets instant yeast near enough
6 g salt            (2%)
18 g butter      (6%)
9 g sugar        (3%)  instant or osmotolerant yeast if you take this to high values

Temperatures
My dough temperature is around 24 - 25 C
The oven temperature is 220 C reduced to 190 C five minutes into bake

Rise time 50 minutes

Mix+ knead time    15 to 30 minutes bread maker dough program

Bake time        35 minutes for one loaf


Pour the hand warm water into the bread maker pan followed by the yeast and sugar then the flour and salt.  Switch on the dough program and add the butter in thin slices when the dough ball has formed to window pane standard and is slapping round the pan, around 10 minutes or more into the program for my machine. The dough is ready when the ball is slapping round the pan again and the butter has disappeared.  At this point stop the program and tip the dough onto the oiled work surface.  (If your dough is not ready when the paddle action ends switch off the program and switch it on again and wait until the dough is ready.  Most of my doughs are ready before the paddle action stops, 17 minutes into the program.)

Note well, the butter procedure is important, put in the dough too soon and the overall strength of the glue is  reduced.

Whilst the mix and knead proceeds lay out the two mats and oil one. I have a small dish of oil, I brush the back of my fingers across the oil’s surface and brush them across the mat.  Three brushes does the trick.  The oiled surface will get streaky that is not a problem.  Coat finger tips and thumbs with oil.

Tip out the balled dough onto the oiled surface, be patient it will come out.  Divide the dough into two equal masses, leaving them on the oiled surface.

Gently roll one of the pieces of dough into a log about 9 inches long so it is covered with an oil film, and using both hands lift it to the dry surface.  Kendal roll it including the squashing and cutting routine then replace on the oiled surface.  Repeat for the other piece of dough.  Leave the ‘sausages’ to rise for 20 minutes at around 25 C. 

You can work with one or two sausages to make the loaf, it depends on the size of your hands.  With a dough cutter make one sausage into two, one larger than the other by cutting along the length of the sausage.

If you are making a round loaf, move the  small one onto the dry surface and Pull Roll it into a wheel after squashing the far end and cut and placing the near end.   Lift it back onto the wet surface. move the larger  sausage onto the dry surface squash both ends then stand the wheel on the near end at right angles to the length of the sausage.  Gather the squashed end onto the wheel and Pull Roll.  Turn the completed Pull Roll catherine wheel shape onto its base to give a  round shape.  Finally lift it using cupped hands onto the baking tray for the remainder of the rise.

If you are using a tin, Kendal Roll the smaller sausage on the dry surface after flattening the far end and cutting and placing the near end, then place it on the oiled surface.  Move the larger sausage onto the dry surface and quash both ends. Add the Kendal Rolled sausage to the nearest end and continue to Kendal Roll when finished lift it into the oiled tin.

 The round dough shapes are easy to handle, pick each round one up by cupping your hands round it, they feel jelly like and hold their shape.   When you put them on the tray you can gently push them into shape if they need it.  Pick up the tin shaped dough sausage by holding your hands as if they were clenched on a horizontal bar in front of you, the bar being the dough sausage.

Dont be concerned at handling the dough shapes.  They are strong even though jelly like.  If the dough put on the baking tray is lopsided push it over until it is a bit lopsided in the opposite direction, hold it there for a few seconds then release.  The correction of the shape can be carried out right up to baking!

I use tins for my toast, sized for my toaster, everything else is round.  

For the record, my light crumb is not an open crumb, that has small coin size holes that stuff drops through.  My crumb is am entanglement of tiny filaments which have more or less open spaces between them and are soft to eat.