The (rye) loaf looks OK from the outside but a couple of slices in and there it is – a hole, separating the top crust from the rest of the crumb.
This is a problem that isn’t confined to rye breads or sourdoughs, but the answers below are mostly relevant to these breads. Here is a list of possible factors contributing to what is sometimes called the ‘handbag’ effect: pick up a slice of your problem loaf by its top crust and you’ll get the picture.
- The dough is too wet – weak rye gluten is unable to hold the gas-filled structure together at the most vulnerable part of the loaf, i.e. the top. Remedy: reduce water in final dough.
- Over-acid production sourdough. If the lactic acid bacteria (LAB) produce too many protein-degrading (proteolytic) acids, the final dough may begin to break down during proof (when the dough is rising in the tin). This may cause a structural weakness in the vulnerable area at the top of the loaf. Remedy: shorten the production sourdough fermentation time and/or reduce the proportion of production sourdough in the final dough (some maths will be required to adjust the amounts of fresh flour and water so that the loaf isn’t too small for the tin).
- Over-proof (rising too long and/or too much dough in the tin). The structure begins to bubble and collapse at the top and falls away from under the top crust which forms a ‘bridge’ that may look OK but hides a crumbly centre.
- Under-proof (not being left long enough to rise in the tin). Sounds paradoxical in view of 3 above, but an underproved loaf will try to expand in the oven and, if it is unable to break through the crust, may produce a distorted internal structure. This may be the explanation if the loaf has risen rather unevenly with a ‘dome’ effect in the middle of the top, suggesting that the dough wanted to stretch further but couldn’t (see 5). Remedy: prove for longer. Expect the dough to rise to nearly twice its original height before it is ready to be baked (assuming it was fairly flat and evenly distributed in an almost straight-sided tin).
- Skinning of the dough during proof. If the dough surface has dried out during proof it cannot expand as much as it wants and the gas bubbles immediately under the top crust will rupture and subsequently collapse. Remedy: prove in a warm, humid atmosphere, e.g. a polythene bag that is inflated to stop it collapsing onto the dough. If the dough surface looks a bit dry and leathery during proof, mist or gently brush it with warm water to soften the crust.
- Weak flour. Rye grain quality varies like wheat. Odd batches can have elevated levels of (naturally-occurring) enzymes which can produce an overactive fermentation and degradation of the dough structure. This may cause a weakening of the loaf structure under the crust. Remedy: try a different source of rye flour.
- Trapped water. If you trap water in the middle of the dough during moulding with wet hands, it is possible that this will ‘blow up’ into a hole as the trapped water vaporises during baking. However, the chances of this always occurring just under the crust are small.
- Tin too wide. Rye gluten (yes, it does have some, but not the stretchy type like wheat) is not very strong, and it can’t easily support the structure of dough in a wide tin. Many tins sold in kitchen shops are a bit low and wide for rye bread. Excuse the commercial, but you can get excellent tins for rye bread at the Bread Matters online shop