(pictures in the next post)
Following Wendy’s request I will try and elucidate some of the mysteries of proofing.
Bread dough is a complex, and not entirely understood system. My knowledge is also limited and I hope the greater experts on this list will correct my more glaring errors.
This is inevitably something of a simplification of the complicated things that are going on as the dough matures. For a fuller explanation refer to a science based baking textbook such “Principles of Breadmaking: Functionality of Raw Materials and Process Steps” by Piet Sluimer, published by the American Association of Cereal Chemists 2005 ISBN 1-891127-45-4
Proofing is the last stage before baking, when the formed and shaped dough is left to rise before being baked. For some bread it is the only fermentation stage; a lot of industrially made and some craft bread is produced with a “no time dough”, where there is no or little bulk fermentation, but instead the gluten is developed using intensive mixing.
Softer doughs need support during proof. This is often in the form of a linen lined basket or banneton. For long breads, like baguettes and batons (in the demo) a folded floured linen canvas couche is used.
To understand what is happening we need to go back right to when the dough was mixed.
When the dough is mixed air is mixed into the dough to form micro-bubbles. These micro-bubbles are key to what happens later. Dough mixed in a vacuum or in a closed mixer with no headspace (such as the Amway system) produces a fine, close and uniform crumb texture.
The density of gas-free dough is around 0.8 L/kg; after mixing about 0.9 L/kg, showing a gas fraction of about 10% of volume. Fermentation increases this to about 1.0-1.5 L/Kg, at the end of the bulk stage, depending on the type of product, and then to around 3.5 L/kg at the end of proof for a typical white loaf, more than tripling in volume. After baking this will increase again to around 5 L/Kg, oven spring increasing the loaf volume by about 50%, and an increase of 5 times over the volume of the just mixed original dough. These volumes are for white bread; bread with bits in them, such as seed breads or whole meal breads will rise less since the bran or other inclusions tend to puncture the gas cells, and in some breads, such as those with a large preferment, there is less fermentable material.
A good clue for the end of the bulk fermentation stage is when, if you slash the dough, you can see small bubbles in the cut surface.
“Knocking back” or degassing decreases volume, but also makes new food available to the yeast, and generally results in a finer crumb structure. In the 1950s or so, a fine even crumb, such as in Pullman bread was thought most desirable, and techniques were optimised to produce such bread. Now a more artisan bread with an irregular and coarser crumb structure is preferred, so different techniques (less degassing, wetter doughs) are used to make what our predecessors would have thought of as badly made bread.
The enzymes in the yeast, or from added enzymes such as diastic malt, or the acid in sourdough start to break the starch down into simple sugars that can be fermented. Over time this degrades the starch, reducing the dough viscosity making the dough seem wetter.
The gluten gells slowly in the presence of water, and this gell forms the scaffolding of the loaf crumb. Kneading, stretch and fold, or intensive mixing, depending on the type of bread, all help the gluten stretch into thin sheets and distribute the gas cells evenly, although the primary force for the gluten development is hydration, and the primary stretch is the expansion of the gas cell walls in the dough.
During fermentation the yeast generates carbon dioxide. This expands the micro-gas bubbles present in the dough from air entrainment during mixing. No new gas bubbles are created, although some may coalesce, and the very small ones disappear. These bubbles are not entirely gas tight – think of them as a leaky bucket. If the production of CO2 from the yeast drops below the rate the gas leaks or dissolves in the surrounding fluid, then the bubble deflates, rather then inflates. If the bread is over-proved the rate of gas production rate drops because the yeast runs out of food. For cells near the outside of the loaf this diffusion of CO2 to the atmosphere is greater than for cells deeper in the loaf. This means that the fragile foam in the centre is surrounded by a layer of tougher, less expanded cells, a bit like a balloon skin. This skin needs to be tough enough to support the fragile inside, but not so tough as to corset the expansion.
Exposure to the air (or contact with the dry canvas banneton/couche) slightly dries this skin, contributing to its toughness. Too dry, and it will be sufficiently tough not to let the inside rise. Too wet, and it won’t be tough enough and collapse before maximum volume is obtained. Ideal conditions are between 70% and 85% relative humidity. A draught will also dry the skin (and cool the dough), and the bread should be proved in draft free conditions, which can be a problem where a fan or forced convection is used to maintain conditions. Professional bakers have special proofing cabinets where the temperature and humidity can be controlled. Craft bakers cover the dough with a cloth or plastic sheet which reduces draughts and slows evaporation. Putting the dough in its banneton or couche in a loose fitting plastic bag, such as a bin liner is a good home solution.
The relative temperature of the dough and its surroundings is important. If the dough temperature is higher than the air, evaporation will be quicker. Lower than the air, and the air near the dough is cooled, and so the relative humidity is higher. However over time the dough temperature will become that of the surroundings, which is why in proofers where the air temperature is much higher than the dough the first dough pieces stick, and the last ones skin.
Disrupt this skin on ripe dough, and the gas from the inside will rush out, the dough deflating.
As the bubble expands the cell walls are stretched. Gluten hardens and gets stiffer under strain, so the thinner parts of the wall stiffen, pulling harder on the thicker bits, so the bubble expands evenly, until the walls get too thin and rupture, releasing the gas. However cell rupture is rare in most correctly proved bread. Typically dough will stiffen slightly as it matures as the gluten hardens by being stretched, and the bubble jostle each other, although some dough, such as sourdough will slacken with time considerably as the acid degrades the viscosity of the starch. The dough will also feel wetter as the dough begins to overprove.
At the beginning of the proofing period the dough is comparatively robust, and so long as the gas is not completely knocked out of it, it can be handled and shaped. At the end of the proof period the gas cells have expanded to nearly at their breaking point, but held together by the slightly tougher less expanded cell layers around the outside of the bread. The dough is now a delicate foam balloon, with the gas cells near their bursting point. Rough handling at this stage will deflate it.
In the oven the gas in the cells further expand aided by the trapped water turning to steam. The wetter the dough, the bigger the holes. The bread rises like a soufflé. Like a soufflé, bottom heat and direct contact with a hot surface to give maximum heat transfer helps volume. The heat cooks and hardens the cell walls. If conditions are right, the expansion will occur before the walls cook and solidify, giving the desired oven spring. Correctly proved dough will give the largest volume loaf, even though an overproved loaf will be bigger going into the oven.
If the dough is underproved it will not reach its maximum volume, as the gas cells start smaller, and will cook before they reach their maximum expansion.
If overproved, then the gas cells at already at their maximum stretch, or even have started to deflate, and the dough will rise little in the oven. The dough may be bigger going into the oven, but does not gain the extra volume.
The length of time the dough takes to prove depends on many things, such as the activity of the yeast, the amount of food available to the yeast, the stiffness of the dough – stiffer doughs prove more slowly as the sugars diffuse less, and most of all the temperature.
Yeast is most active at about 30C/90F. Above that temperature activity decreases sharply as the yeast begins to die or go dormant. Below that temperature the yeast roughly declines by 10% of each degree C. Thus at 20C/68F the yeast activity is halved.
(Sourdough yeast and lacto-bacillus activity derived from work by Ganzle)
Proof time is also affected by the amount of yeast in the dough. Although the total volume of gas produced is nearly independent of the amount of yeast, being governed by other factors such as the amount of available food and oxygen, the rate of production is can be varied. Craft bakers compensate for lower temperatures, for example when the bakery is cooler in the winter, by increasing the amount of yeast.
In general, straight yeast dough is proofed after about an hour, sourdough after about 4-5 hours at 30C/85F.
All sorts of other complex reactions are going on in the dough, each of which has differing degrees of temperature sensitivity. For example the breakdown of starch into sugars is less temperature sensitive than yeast, as is the activity of the lacto-bacilli in sourdough. Slowly fermented breads tend to be more flavoursome than quick fermentation. By adjusting proof temperatures, yeast amounts and corresponding proof times the skilled baker can to some extent alter the flavour profile of their bread.
The extreme example is where the bread is retarded, cooled to fridge temperatures (4C/40F), so that practically all yeast activity ceases. The dough can be stored this way for up to 72 hours, for example over a period when the restaurant or bakery is closed. During this time other processes continue, most notably the skinning of the outside of the dough and the breakdown of starch into sugars. Retarded doughs have a characteristic reddish crust, from the extra sugars, with fine blistering, but tend to be more flavoursome. The cold also stiffens the dough, and this can make handling of wet doughs easier.
The dough doesn’t cool in an instant. A typical loaf takes about 2-3 hours to cool down, during which time there is still some activity. Thus an overnight proof in the refrigerator is about equivalent to 2 hours at room temperature. It also takes about 2-3 hours to warm back to room temperature, during which time activity will restart.
Whether to bake from cold, or allow the loaf to regain room temperature before baking is still a matter of debate. If allowed to warm there is the danger of over-proving. Personally I prefer to bake from cold. I find the cold dough stiffer, and so much easier to handle, especially for wet slack doughs. The extra temperature change in the oven gives, I think, a greater gas expansion and hence a bigger oven spring. However this larger spring means that unless evenly made and correctly slashed, the bread may bulge unevenly, with the centre expanding more.
“A l’ancienne” is a technique where the dough is mixed cold, and then retarded. The long cold period allows a long period for enzymatic breakdown of the starch into fermentable sugars but because of the cold there is little yeast activity, so that when the dough is later warmed up the yeast has more food available than would otherwise be the case. With slack dough it can give a highly aerated open structure.
Just before the bread goes into the oven, the baker slashes it. The slashes (“gringe”, French for grin) act as weak points in the crust, allowing the dough to rise evenly in a controlled fashion. Without the slash the bread is likely to tear or bulge, and the rise will be impeded. It needs to be done just before the bread is put in the oven so that not too much gas leaks out – the heat of the oven will replace the gas that is lost. For this reason the slash should be quite shallow, and cut at an angle of about 45 degrees, almost cutting a flap. For plain breads use a very sharp thin knife, traditionally a razor blade on a stick (“lamé –French for blade). Special disposable ones can be obtained from http://www.scaritech.com/ . For seeded breads a serrated knife can sometimes be easier.
Slash quickly and positively – don’t go back and mess with the bread.
By tradition a baguette has seven slashes, nearly parallel to the length of the baguette, that open into a pleasing lattice. Originally the slash pattern allowed a housewife to identify her bread in the communal oven, but now is used decoratively. For example Poilane http://www.poilane.c...1595520020 carves a stylised P into their bread.. Bold simple shapes work best.
It is hard to tell whether raw dough is under, ripe or over-proved, except in extreme cases. If you make lots of the same loaves you can begin to get a feel for when it's ready – from the volume, the look of the crust, and the slight resilience. It should feel taut, a little like a balloon, with a slight resilience and bounce back if lightly pressed. However the changes are very subtle.
One technique is to put some dough into a glass measuring cylinder or jug. When the volume has about tripled from the initial mix, the dough is ready.
It is slightly easier to tell from the cooked loaf. Underproofed bread will have a lighter crust (no so many sugars from the enzymatic action), a less expanded gringe, and a tight crumb. Overproofed dough, by contrast will have a darker, reddish crust, little oven spring, narrow grigne, and an open, but somewhat coarse crumb.
Back to Wendy’s original questions:
What's an over proofed dough look like? Before you bake it and after it's baked.
An overproofed sough will be very fragile, and may collapse. Baked, it will have little oven spring, so the grigne (slashes) will not open much. The crust will be redder, and possibly burnt in places from the high sugar levels.
An underproofed dough will not have its full volume, and the crust will be pale. The crumb will be closed and tight.
What's an under proofed dough look like? Before you bake it and after it's baked.
No, they are the same signals. It is easier to over-proof using a proofer. If the humidity is too high it can interfere with the formation of a taut skin, leading to earlier collapse.
Do your signals become blurry when your using a proofer verses at room temp. or retarding?
Are there different "signals" you look for in different types of bread or is it basically the same regardless?
They are basically the same signals. However wholemeal breads, and breads with inclusions in them will not rise as far. Relying on the bread to double in size, although a reasonable rule of thumb is not always accurate, and can often lead to overproving. If you bake frequently you will soon get used to what your particular bread should look and feel like.
And how does your slashing effect your oven spring....relating to over proofed or under proofed bread?
Too many or too deep slashes will deflate the loaf, as will waiting to long between slashing and baking. Slashes also break the taut skin, so allow the loaf to spread.
The effects are much more serious in overproofed bread.
How do you 'read' the texture to decipher where you've gone wrong?
See the picture post...
A quick summary of things that matter in bread making:
Hydration: the ratio of the total amount of water to flour. Dough behaviour changes rapidly over a small change in water content: few percentage change – a tablespoonful of water in a pound of dough can make a dramatic difference. Of course, different flours can adsorb different amounts of water. Wholemeal will adsorb maybe 10%-20% more. Higher gluten flours can tolerate higher hydration levels. However what this means is that for repeatable results you need to be accurate in measurement – use weight not volume, and make sure not too much extra flour is not picked up from your worktop, or water lost in mixing.
Dough temperature: Yeast activity and hence proof times vary greatly with dough temperature. The dough temperature can be affected by how much work the mixer does on the dough, the temperature of the ingredients and the ambient temperature.
Degree of proof: Sourdough is reasonably tolerant to the degree of proof since it’s a slow process. Yeast dough, since it is moving faster, much less so, and overproving is the biggest cause of failure.
Things that don’t matter so much:
Strength of flour: You can make good bread from almost any flour. Strong flours can adsorb more water and are somewhat more tolerant, but most European bread, such as French Baguettes are best with the local soft flour.
Additives: Additives can help, give a wider tolerance, but are not critical, and in larger doses will both affect taste and disguise the signals you need to look for.
Handling: Providing it is correctly proved, dough is pretty tough stuff. Overproved dough will deflate soon as you look at it. So long as the dough is mixed evenly, you don’t need to knead – stretch and fold works fine. Nor do you need bulk fermentation for many breads.
Edited by jackal10, 01 February 2006 - 12:51 PM.