Crust me!

July 24th, 2014 | Posted by greg in Daily life...

Baking bread in a city surrounded by water and by tropical climate, humidity and rain fall is pretty much a science on its own. There are several reasons why one can’t find better bread in Hong Kong, and it has to be said that one of the most important factor, independent of the baker’s hand, is the weather. Of course, there are some bakers out there that don’t really put the effort in baking better bread, yet there are some doing it. I think this point is to be explained a bit more to find out why bread is not always “like back home”… well, to start with, here is the news, the relative humidity “back home” is roughly 30% to 40%. Hong Kong is in the range of 80% to 90%. If you are not into technical reading, then click here, if not, carry on reading…

We’ve all tasted bread back home with a crunchy texture and beautiful snap crunch sound. How disappointing it is when we live in our lovely Hong Kong and can’t put our hands on that same perfectly crunchy loaf. Rest assured, neither can I… There are two main reasons affecting the crust texture. It’s the relative humidity and the Activity of Water (aW) within the crumb, a standard measuring factor in food manufacturing, notably used for calculating conservation time and mold development in food. To give you a very simple picture of the situation, look at a slice of bread like the one below:

Super soft and buttery texture

Pistachio & Beetroot Brioche – Super soft and buttery texture

As the crust is crunchy and thus of low water content, the ambient humidity is being absorbed by the crust on the outside of the bread. But at the same time, the water in the crumb also migrates outward to the crust from the inside. This is the very reason why keeping bread in any sort of sealed container to keep it dry won’t work; the dryer the environment is in a box, the more the humidity from the crumb will move towards the crust, hence bread getting stale when kept in plastic bag for example. When bread is kept in a plastic bag at room temperature, mold will develop at a faster rate. Hence the commercial bread in plastic bag not developing mold because they are LOADED with chemical mold inhibitors; yet another great and healthy feature of industrial bread. (read sarcasm here…)

On the table below, you can see the variance of aW and moisture. Everything has been tested scientifically and there is no magic way to keep your bread crunchy in that sort of environment beside the simple fact of baking it freshly and using it then.


On the second table you can see the variance in humidity, for example simply due to the fact that a plain bread without salt will attract less moisture as salt is hygroscopic. 

Overall, we have noticed that using sourdough as a leavening method gives a longer crunchy shelf life to the breads. I believe the properly gelatinized crumb as well as the nicely caramelized thick crust has a positive effect on keeping the crust crunchy for a longer time. Breads made on short fermentation using commercial yeast on the other hand are getting soft faster, mainly due to the very thin crust. Well hydrated sourdough bread can get back their crust by baking them for a few minutes to extract the soaked humidity from the crust; thanks to the high hydration of the crumb, the bread will find its crispy crust back and the crumb will remain nicely hydrated. The opposite would happen on directly fermented bread with commercial yeast with normal hydration where the crust will certainly snap again, eventually crumble off the bread, but the crumb being less hydrated, will end up drying and giving you chewy bread. To sum up the situation: in a dryer climate you get a crunchy loaf that dries over time, in tropical weather you get a crunchy loaf that molds.

Conclusion: Bake fresh with sourdough and LOVE! 


Table source: Cereal Chemistry, p.132

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