The interior texture of your bread -- the soft part you see when you slice it open.
Crumb structure tells you a lot about how your fermentation went. An even distribution of medium-sized holes usually means good fermentation and shaping. Large, irregular holes ("open crumb") can be the goal for some bakers but can also indicate uneven fermentation. Dense, tight crumb with tiny holes often means underfermentation. Gummy crumb with large tunnels near the crust ("fool's crumb") is a classic sign of cutting the bread too soon or underfermentation.
