Scalding - what is it?
Scald. Choux. Tangzhong. Mashing. Gelatinised starch. There are many strange words followed by many different process recipes. What are they? Why do we need them to bake a loaf? And why so many techniques? I will try to answer these questions in this post.
I believe English speaking baking communities got introduced to flour scalding through Japanese Hokkaido milk bread, but gelatinisation of different kinds is used all over the world: most of Latvian rye breads are scalded, French chefs are making choux pastry and the whole beer brewing process starts with mashing everywhere in the world. It is a very common process in grain preparation and cooking.
Let’s start with a chemical process common to all methods. This process is called starch gelatinisation.
Oh, and by the way, this post is HUGE!
Starch is a term which refers to a whole group of complex polymeric carbohydrates insoluble in water. It is produced by all plants as a store of energy and each starch molecule is made out of multiple glucose and amylose molecules. Starches produced by different plants are different and have different chemical and physical properties, but they share plenty of similarities. One common property is that when starch and water mixture is heated up water gets absorbed by starch. This is called swelling and it is a first step in gelatinisation. Swelling temperature varies between starches. For example, wheat starch starts to swell at about +65C while rye starch needs only +55C. In general most of starches swell in the range between +55C to +85C.
Once swelling occurs amylose molecules start to dissolve into water. Dissolved amylose starts to leach from the starch and granular structure disintegrates. Water also gets trapped inside damaged starch molecules.
Gelatinisation has two important consequences:
- It allows starch to absorb large amounts of water.
- It makes starch digestion easier for both humans and micro-organisms like yeast and lactic acid bacteria.
Limited starch gelatinisation also happens during baking once the dough heats up to +65C inside and it contributes to bread rise and crumb structure as much as gluten. Breads from grains naturally low in gluten or with limited gluten development like rye and barley can only rise due to gelatinisation.
But once this mixture starts to cool down another process happens.
When gelatinisated starch cools down its molecules gradually aggregate and form a gel. Retrogradation is different between different starches and every cook should’ve noticed that some starches will form either strong gel, soft gel or will disintegrate into a lumpy mess. This is why all thick sauce recipes call for a specific type of starch source.
Strong gels usually restrict amylase bio-availability and reduce starch digestibility (compared to hot gelatinised state). Weak lumpy mess usually loses the water. Wheat starch forms strong and stable gel. Rye starch forms soft and stable gel. Stable gel is very important for bakers as it is the primary container of moisture in baked bread. The more starch molecules get gelatinised during bread making the longer resulting bread will stay fresh and moist.
Retrogradation is also important in rye breads. If a rye bread is cut while hot or even warn, it will be very sticky and will feel unbaked. Retrogradation helps crumb to set and turn into a proper bread. This is why rye breads should be left alone to cool down properly for at least 12 hours. The same is true for wheat breads to some extent, but presence of gluten helps the crumb to set a lot faster, so generally baker should only wait for wheat bread to come down to room temperature. Pastries with low gelatinisation level (which is inhibited by sugar and eggs) can be eaten warn.
More information about these processes can be found here.
There’s another group of carbohydrates important in bread baking - pentosans. Pentosans are also polymeric carbohydrates, but they are made out of pentose molecule instead of glucose. They are present in all grains used in baking: wheat, rye, barley, etc. And they also swell similarly to starches. Pentosans usually swell between +30C to +50C and form sticky pastes which can trap gases similarly to swollen starches. Their quality is extremely important for rye bread baking, but they might also inhibit gluten formation in wheat breads.
With all that said we can conclude that starch and pentosan gelatinisation of flour serves several purposes:
- To make complex carbohydrate polymers more digestible for both humans and micro-ogranisms responsible for fermentation of the dough.
- To absorb and hold water increasing shelf life of bread.
- To make bread softer and tastier.
Last point might not be so obvious, but gelatinised flour makes bread very soft. I mean, just try good Hokkaido milk bun! It’s like a cloud in your hands! The same is especially true for rye breads which can be quite stiff sometimes. At the same time gels tend to restrict overall rise quality to some extent. Breads without any type of scald will always have a better rise. Thus scalding should be done carefully to improve softness and taste just enough without turning your loaf into a pancake.
Scalds can be categorised in multiple different ways: by gelatinisation degree, by saccharinification degree, by fermentation, by flavouring additives and by preservation.
Starch swelling and amylose leaching depends on temperature and time. The higher the temperature and longer the process the heavier starches will be damaged.
For example, tangzhong technique is fast and cool: flour and water mix is slowly warmed up to +65C after which heat source is removed almost immediately and cooling down starts. This process allows starches to absorb additional water without much degradation and amylose losses. Rheological properties of the dough with such scald are barely affected yet resulting bread gets more moist and soft than usual.
On the other side of the spectrum are Latvian rye breads where part of the flour is scalded with boiling water and then is kept at +65C for a few hours or even overnight. This process turns flour and water mixture into slightly sweet and very sticky slurry which has a very big impact on the final dough both in terms of rheological properties and nutrient richness for fermenting micro-organisms. Such scalds can be used to boost fermentation intensity which is important for rye baking, change texture and flavour of the bread as well as to make crumb very moist and capable of being fresh for weeks when stored properly.
Saccharinification is the process in which complex carbohydrates like starches get broken down into their monosaccharide building blocks like glucose. This process most commonly occurs through enzymatic hydrolysis in which enzymes cut long polymers into standalone sugars. Saccharinification is the core of beer brewing: mashed grains are first heated to their respective gelatinisation temperature, then enzymes are added to break down swollen starches into glucose and to turn the whole mash into a syrup.
A similar process is used for some scalds. Once scalded flour reaches +65C some source of enzymes is mixed in and it is left at such temperature for a few hours. The end result is sweet syrupy liquid which is then used as a fermentation booster and sweetener for final bread. The main difference with brewing process is that brewers add a lot more enzymes to ensure that all sugar content is extracted from the grains while bakers add low to moderate amounts of enzymes to break down flour partially so that resulting bread still retains moisture and has a soft crumb.
Enzymes can be added as a rye or barley flour or as a rye or barley malt flour. Normal flours will have low amounts of enzymes while malts will have high amounts of enzymes. Type of enzymatic booster and its amount regulates saccharinification degree and the speed of the process. If normal flour is used then such scald is called “self saccharinified scald”. If malt is used then such scald is called “malted scald”.
Successful saccharinification requires high gelatinisation degree.
Some scalds undergo additional fermentation step before ending up in final dough or they can be a part sourdough starter as a food source instead of plain flour and water mixture.
Fermented scalds are used to develop specific flavour profile for bread and to boost micro-organism activity before mixing final dough. Such scalds are characterised by sweet and sour taste and fruity aromatics. Thermophilic lactic acid bacteria cultures are usually used for scald fermentation.
Scalds can also be used for sourdough culture feeding. Mesophilic cultures can be fed by a scald to fasten the process or to help yeast and bacteria colonies to establish themselves when starting new culture development. Scalds are also a primary food source for thermophilic cultures as such cultures require high temperatures to live and grow.
Sometimes aromatics like seeds and spices are added to scalds at the start of preparation process. This aids breaking down protective layers and releasing aromatic compounds into the scald. Common aromatics in scalded rye breads are caraway, cumin, coriander, fennel and anise seeds. Another common flavouring in Russian breads is fermented rye malt which is not enzymatically active. Flavoured scald will boost bread flavour and will evenly distribute aromatics inside the crumb. Seeds can be added whole or crushed.
Sometimes scalds are prepared with added salt. Salt usually improves starch gelatinisation and acts as a preservative for short term storage. For long term it is better to freeze scald portions and use them after defrosting. Salted scald can also be used as a lactic acid bacteria growth medium as salt inhibits many unwanted microorganisms. It is better to dilute salt in water first before adding flour and heating everything up as salt dilutes better in cold water.
There are different ways to classify scalds thus there can be scalds identified by complex denomination, for example, flavoured highly saccharinified fully gelatinised malted scald. That all can be quite confusing, but once you start making them following existing recipes they will quickly become your second nature and you will start experimenting with them on your own. And just when you thought this article would end I present you another wall of text describing multiple different ways of making scalds.
There are multiple ways to create a scald, but there are only two general approaches: to heat everything up or to cool everything down to desired temperature. Scald hydration is usually between 200% to 400%. Sometimes this high hydration leads to a situation where all of water in bread recipe is contained in a scald and sourdough and none is added when mixing final dough.
This is a traditional approach in Northern and Eastern Europe for many rye breads and for some wheat breads. Flour is measured, then boiling water is added in three steps and mixed in thoroughly as fast as possible to avoid excessive mixture cool down. Any lumps should be avoided during mixing and mixing container is usually preheated before adding ingredients.
If saccharinification is desired, then once everything is mixed properly the scald is cooled down to +65C before adding enzyme source. It is then left covered at +65C for 1.5 to 5 hours depending on enzymatic activity level and desired results.
If saccharinification is not required then the scald is immediately cooled down to a temperature compatible with dough mixing which is usually from +25C to +35C depending on a bread recipe.
Scalds are always cooled down naturally to allow proper retrogradation.
This method is hard to execute with small amounts of flour and water as small amounts will cool down below +65C very fast, often before all lumps are eliminated. But it works better with large amounts when mixing container can not be put on the stove to heat mixture up. Large amounts will also cool down over long periods of time meaning that container can be simply left on its own without external heat source to saccharinify the scald.
This is the way tangzhong scald is made. The same method is used by brewers to mash their grains and it is quite popular in food preparation to thicken things.
The flour is mixed with cold water until even batter like mixture is achieved. Then it is slowly heated up to a desired temperature while stirring constantly. Flour is usually heated up to +65C if minimal gelatinisation is desired. Then such scald is cooled down to a dough specific temperature as described in previous method description.
When higher degree of gelatinisation is desired scald can be heated up to a higher temperature up to +95C. Corn or potato starch slurries can even be boiled for some time.
If the recipe calls for saccharinification then again enzymes are added once the scald is at +65C and the process is followed as described above.
Heat up method is used when partial gelatinisation is required or when the amount of ingredients is small and cool down method becomes hard to execute. For example, I use heat up method when baking a single loaf up to 1.5kg, this way I can get rid out of all lumps before heating the scald and get nice and even result without a rush.
It usually takes about three hours to create a saccharinified scald and it should be finished at the same time as a sourdough so that they can be both mixed into the next development stage. Sometimes it can be hard to get the timings right to fit into busy life schedule. Thankfully it is possible to run saccharinification at slower pace to do it in 8-12 hours.
Once enzyme booster is mixed in, scald should be placed into the oven at +65C for 30-60 minutes. Once this step is done oven can be turned off and scald left inside in slowly cooling oven for 7-11 hours and it should be ready. Don’t forget to cover it tight or it will lose a lot of moisture while cooling down. 8-12 hours process should match sourdough development time and both should be ready together.
Flavours are usually added at the start of the scalding process so that they can integrate better into the mixture. Only heat resistant flavourings should be added. Aromatic herbs can overcook and give bitter off flavor into the final bread. Aromatic seeds, including black pepper, are usually the best choice.
This wall of text is coming to an end. Scalding is an important technique which can improve bread quality and flavor, but it should be used carefully. Usually 5% to 20% of flour are scalded one way or another (malt is counted as flour). Higher percentages usually result in poor rise.
Gelatinised starch can also be added by other means. One common method is to add boiled or baked potatoes to the dough. Some recipes have small amounts of corn or potato starch powder or rice flour. All in all this is a well known method of improving breads used by many cultures in different ways.
P.S. 22.05.2020 update: fixed typos, fixed temperatures.