Key Recipe Ingredients and How Those Impact the Crumb Structure Quality

Bakers have long known that ingredients and processing steps must be carefully controlled to obtain an optimal crumb structure. Over the past 30 years, scientific studies have elucidated many of these effects. The development of a porous crumb depends on the formulation (recipe) and the process (mixing, fermentation, baking conditions)¹. In this part will discuss how key recipe components influence crumb structure quality.

Key recipe ingredients influencing crumb structure:

• Flour type and gluten content: The protein quality of flour sets the foundation for crumb structure. Wheat flours with higher protein (gluten) content and good-quality gluten generally yield bread with greater gas-holding ability and thus a more expanded (developed) crumb. Strong gluten forms elastic cell walls that stretch rather than break when gas expands (unless it’s too strong ☺). For instance, bread made from strong bread flour will have a higher volume and a finer, well-defined crumb grain compared to bread from low-gluten pastry flour, which we may expect will give a denser crumb due to insufficient gas retention. If gluten strength is too low (as in some ancient grains or flour substitutes), the dough cannot retain CO₂ well, leading to small loaf volume and tight crumb. The extreme examples are 100% rye bread or gluten-free bread. While it is still possible to bake a decent (and delicious) bread from pure rye flour, its quality characteristics will differ from those of wheat bread. One should expect a heavy crumb with moderate to low porosity and thick cell walls. This is because gluten development is hindered by a high level of arabinoxylans (AX), and crumb formation is done by the starch–AX system, with protein playing a relatively minor role.^2,3 For the gluten-free bread, which without gluten network tends to have very low porosity and a cake-like crumb. To address this, researchers incorporate structure-building alternatives like hydrocolloids (e.g. xanthan gum, hydroxypropyl methylcellulose), fibers (e.g. psyllium husk), alternative proteins (e.g. egg white) in gluten-free formulations to improve crumb quality. These additives mimic the viscoelastic properties of gluten, yielding higher loaf volumes and softer crumbs in gluten-free breads.⁴ On the other hand, using flours with different starch properties can also affect crumb: one study showed that substituting normal wheat flour with waxy wheat (which lacks amylose) improved product volume when added at low levels but resulted in a significant collapse of the baked good item when >30% waxy wheat flour was added.⁵
• Water (hydration level): Water content in dough directly affects crumb structure by determining dough viscosity and gas bubble mobility. A higher hydration dough (softer dough) tends to produce bread with a more open, large-celled crumb, as the dough is extensible and bubbles can merge or grow larger before the structure sets. Many rustic or artisan breads use high hydration (70% or more water relative to flour) to achieve an open crumb with irregular large holes. In contrast, a stiffer, lower hydration dough yields a finer and more dense crumb structure because the dough resists bubble growth and promotes many small bubbles (pretzels we like ☺). However, too low hydration can limit expansion and result in a dry, tight crumb. Optimizing hydration is thus key: for example, pan breads often target moderate hydration (~60%) to balance bubble expansion and stability, yielding a soft yet uniform crumb. Water also affects the extent of starch gelatinization during baking. Generally, within “normal” ranges, more water in dough improves crumb softness (since it gelatinizes more starch), but bakers must control other conditions to bake a good quality bread. Talking about more robust science – there is a comprehensive study that systematically investigates how varying hydration levels (limited, partial, and full) influence the morphological, structural, and molecular properties of gluten proteins during dough mixing. Using techniques such as scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), and size-exclusion high-performance liquid chromatography (SE-HPLC), the researchers observed that higher hydration levels facilitate the rapid formation of a more compact and continuous gluten network. However, these networks are more susceptible to mechanical disruption during mixing. SE-HPLC analysis revealed significant depolymerization of glutenin macropolymer (GMP) in fully and partially hydrated samples, indicating that hydration level affects the molecular weight distribution of gluten proteins. Fourier-transform infrared spectroscopy (FTIR) showed that higher hydration levels promote the formation of more ordered secondary structures, such as α-helices and β-sheets. Additionally, sufficient mixing increased ionic and hydrogen bonding, while excessive mixing led to the exposure of free sulfhydryl (-SH) groups, suggesting potential over-processing. The study concludes that hydration level and mixing time are critical factors in determining the gluten network’s development, impacting dough rheology and, consequently, the quality of wheat-based products.⁶
• Water (physical and chemical properties):

  The hardness of water, defined primarily by its calcium and magnesium content, influences gluten strength and dough handling characteristics. Medium-hard water (100-150 ppm) offers the best balance for gluten formation. In this range, minerals strengthen the gluten network, improving dough stability and gas retention, which enhances bread volume and texture. However, very hard water (>200 ppm) can overly strengthen gluten, resulting in stiff dough that is difficult to process. This can limit expansion during fermentation and baking, producing dense loaves. Conversely, soft water (<50 ppm) often leads to insufficient gluten development, resulting in sticky dough and lower gas retention.

  In addition to hardness, specific minerals in water affect fermentation and yeast performance. Calcium and magnesium ions not only impact protein hydration but also influence enzyme activity and dough oxidation levels. Excessive mineral levels can negatively affect dough extensibility and increase mixing time, which may harm product uniformity. Importantly, the presence of sodium, iron, copper or manganese in water can interfere with yeast and enzymes activity, particularly if present at elevated concentrations (more on the salt role in baking later below). These interactions can lead to issues with fermentation, development of off-flavours e.g. degrading final product quality.

  The pH level of water is another crucial variable. Ideally, bread making benefits from neutral to slightly acidic water (pH ~6.0–7.0). Alkaline water (pH > 8) can reduce yeast fermentation efficiency, delay gas production, and negatively affect dough rise and bread volume. Acidic water, on the other hand, may slightly improve gluten hydration but could also affect flavour balance. Additionally, the use of chlorinated water – common in municipal systems – can inhibit yeast growth and activity. Chlorine, especially in its free form, is antimicrobial and may damage the microbiological balance needed for robust fermentation. It is recommended to use waters’ filtration or dichlorination for optimal yeast function, particularly in artisan or sourdough bread production.

• Yeast and fermentation (leavening): The amount of yeast and fermentation time/conditions control how much gas is produced and how the bubble structure develops. Yeast level: Using more yeast or a faster-fermenting yeast strain will create CO₂ rapidly, potentially leading to a very aerated dough. If not managed, this can cause processing issues and formation of large, uneven cells leading to over-proofing. On the other hand, too little yeast or a very slow fermentation yields fewer, smaller gas cells – resulting in a low-volume, dense crumb. Bakers often adjust yeast to achieve a balance: e.g., sweet doughs with high sugar require special osmotolerant yeast or longer fermentation to compensate for sugar-slowed gas production.⁷ Fermentation time: Allowing the dough to proof for the right length is critical. Under-proofing (insufficient fermentation) means the dough hasn’t expanded fully, so the baked bread will have a tighter crumb with undeveloped small cells and lower volume. The loaf often loses its shape because the crust tears from the strong gas release and rapid expansion during baking. Once the crust sets, any remaining pressure inside continues to push outward – almost like a small 'bomb' going off inside the bread. Over-proofing (excessive fermentation) can be even worse for structure: the gluten network is over-stretched and weakened, and many cell walls rupture or coalesce. Over-proofed bread often has very large irregular holes and areas of collapsed crumb. Studies have shown that over-proofing leads to thin cell walls, increased cell size and higher overall porosity, which paradoxically can make the crumb structure weaker and more prone to collapse⁸. Essentially, the crumb over-expands and then cannot support itself, resulting in its compromised quality. Temperature during fermentation also matters: warmer dough ferments faster (producing more but potentially coarser gas cells if too fast), while cooler, longer fermentation (as in artisan sourdough processes) often yields a more nuanced, open crumb, particularly when combined with high hydration rates (>70%). In sourdough breads, natural fermentation with wild yeast and lactic bacteria usually requires longer times; the acidity can tighten gluten somewhat, leading to a moderately open but not giant-celled crumb, with a moist texture.
• Ingredients like sugar, milk, eggs, and fats (which enrich the dough) all impact crumb structure. Sugar provides food for yeast up to a point, but high sugar levels (>10% on flour weight, as in sweet rolls) actually slow down yeast activity (high osmotic pressure) and can reduce gas production.⁸ Thus, very sweet dough often ferments slowly and can have a closed but even crumb structure unless extra yeast or specialized yeast is used. However, sugar also tenderizes crumb by competing for water (in this case, less water for gluten means a more cake-like crumb texture) and by contributing to browning through Maillard reaction. Fats and oils (e.g. butter, shortening) play a dual role: they lubricate and weaken the gluten network (leading to a softer, finer crumb) and importantly, they help stabilize gas bubbles. Research by Brooker (1996) demonstrated that solid fat particles can coat gas cell surfaces during mixing and early baking, acting as stabilizers that prevent bubbles from coalescing. In essence, within certain level, fat strengthens the walls of bubbles by forming a hydrophobic film, resulting in improved gas retention and a more uniform crumb structure.⁹ This is why adding a bit of fat often increases loaf volume and gives a finer, tender crumb (classic sandwich bread contains 1-5% fat for this reason). Too much fat, however, can collapse structure by excessively impacting the dough stability (extreme example: brioche with 50% butter on flour weight – is very rich and soft but needs careful handling to maintain structure). Eggs (used in brioche, challah, etc.) add lecithin (an emulsifier) and proteins that can strengthen but also tenderize – they generally help create a rich, yellowish, finely “bubbled” crumb that is soft yet holds its shape. Salt adds not only flavour but also tightens gluten and controls yeast activity. A normal salt level (1.0%-2.0% of flour) improves crumb structure by strengthening the dough (preventing overly large holes) and moderating fermentation for a more even gas distribution.^10,11