Several months ago I asked Digest readers for help with the baffling limp
crusts I encountered when making bread from highly hydrated doughs (at or
above 85%). This is an update, both for those who responded and for anyone
else who wants to make these breads CRUNCH.
The following covers the practical solutions I've found, but I had also
hoped to provide some useful science background. Unfortunately it will
take me a good while to understand it all, and as a result the comments
that appear below only represent my (weak) understanding of a complex process.
Limp crust syndrome:
As a crust lover I am in the habit of baking normally hydrated breads (up
to 75%) for five or ten minutes at a high temperature 500F (260C) then
dropping the temperature to 450F (232C) until the crust is a rich
brown. This provides a crunchy crust with lots of color. When similarly
baked doughs with 85% hydration come out of oven they look just as good,
including a firm crust. But with as little as 15 minutes of cooling the
crust becomes very soft, thin, and flaccid - almost like a sagging skin
that's loosely attached to a heavier, interior mass. Once this meltdown
sets in, the crust is never the same.
Kitchen experiments:
A solution came from a kindly professional who advised me to try again at a
lower temperature. This I did, putting an identical bread (recipe appears
below) in a 400F (204C) oven, and taking it out when the crust color
indicated the bread was done. (Note: there was no time with the oven door
open, or other curing tricks.) The result was fabulous, with a crust that
is yielding but definitely crisp, marked by many small bubbles and an
almost laminated (layered) cross section. The crumb is pleasantly holey
and very even in texture, though not so creamy as the limp crust examples.
This first success lead me to wonder where the limits on hydration might
be, at least at this temperature. To explore the possibilities the
above-mentioned dough was adapted with the addition of sufficient water to
raise the hydration level to 98%. This bread is too soft to stand on its
own, so a few changes in handling were required to approximate the volume
of the first (recipe below). While it took over 70 minutes in the oven,
the result was very pleasantly edible and with a crust very similar to that
described above. When I waited for the loaf to wilt as it cooled, nothing
happened.
In my call for help and subsequent conversations with Digest readers the
consensus was that water was in some way responsible for the limpness, and
that finding a way to reduce the bread's after-baking water content would
be beneficial. This was partially confirmed when the weights of two loaves
- one baked at the high temperature, one at the lower - showed that the
former weighed substantially more than the latter, presumably due to higher
moisture retention. And water was indeed the culprit, though in a more
complex way fashion than might first be thought.
Technical stuff:
The root of the problem is fairly simple, and well described by Harold McGee:
"Immediately after being removed from the oven, the loaf of bread is far
from being a homogenous body. The outer layer is very dry and close to
400F (204C), the interior moist and around 200F (93C). During cooling
these differences slowly even themselves out. Moisture diffuses outward
and heat from the surface, both inward and out into the cooler air."
(McGee, p. 310)
A more intricate description comes from French bakers, who have identified
limp crust syndrome with a term of their own: Pain Saisi. One writer
described it this way:
"A bread's crumb is sticky when the baking is flawed: the most frequent
cause is putting [the bread] into an oven at too high a temperature; the
crust will be caramelized before the interior has time to cook - In the
preceding case the crust, strongly colored, is hardly formed, and after
several minutes of cooling it becomes very limp." (Guinet, p. 169)
As noted in the last sentence above, limp crusts are not only prematurely
browned, but only partially formed. The same writer adds:
"Until 100C evaporating water from the crumb hinders crust development; the
crust is essentially only a film. The water vapor released, in effect,
helps slow the penetration of calories [heat energy] into the dough, the
temperature above that being notably lower than that of the surrounding oven."
"Above 100C the crust dehydrates slowly while solidifying. "
"Finally, and at the same time, the sugars remaining in the dough undergo
dextrinisation then carmelization, marking the beginning of the coloring of
the crust, finally giving, by reaction with certain protides, products of
roasting and grilling. This is what is referred to at the Maillard
reaction." (Guinet, p. 59)
Guinet notes that in the oven bread dehydration comes principally from the
crust area, and the crumb retains nearly all of its moisture. One reason
for crust water loss during baking is straightforward evaporation due to
the heat and low humidity of the oven. But another, more interesting
phenomenon is the loss of water as it is retracted into the crumb. As
Guinet puts it:
"Every difference in temperature in a wet body provokes a transfer of water
toward the coldest spot." (Guinet p. 62)
"This temperature difference is due both to the thermal inertia of a lump
of dough, and to the different ways that each part of the dough is warmed:
the exterior is heated by the radiant heat of the oven, but the interior is
heated primarily by conduction (we all have our baking stones, right?)."
(Guinet p.61)
Conversely, it is only during cooling that the crumb experiences a notable
water loss, for the same reasons. The crust cools more quickly than the
interior, prompting the interior moisture to move outward. This process
continues through the cooling period (up to 24 hours) until there is an
equilibrium between the different parts of the bread and their storage
environment. As as the water moves outward, it damages the crust -
sometimes a crust that wasn't full developed anyway.
Sources:
Raymond Calvel, Le gout de pain: comment le preserver, comment le retrouver
(Editions Jerome Villette, 1990)
Roland Guinet, Technologie du pain francais (Paris: Editions P.B.I., 1992)
Harold McGee, On food and cooking: the science and lore of the kitchen (New
York: Scribner, 1984)
Recipes used:
Uptown Rustic v. 4.1 (Makes one loaf of about 1,200 grams)
Step. 1: Mix sponge
250 grams King Arthur Sir Galahad (or similar unbleached white flour, about
11% protein)
280 grams water
1/2 tsp yeast
Mix, leave at room temperature for 1 hour, then refrigerate overnight
2. Mix dough
All the sponge
460 grams King Arthur Sir Galahad flour
40 grams General Mills All Trumps (or similar hi-gluten 14% protein flour)
360 grams water
1/4 Vitamin C tablet (500 mg), crushed
Mix and let stand 20 minutes
Step 3: Salt and knead
Add 15 grams salt. Knead with mixer until a gelatinous, shiny steel grey
(about 15 mins on Kitchen Aid speed 6)
Step 4: Ferment
Let rise until doubled in volume
Step 5: Shape and let rise until doubled (in basket or free form)
Step 6: Baking:
Put into 400F oven, with steam for first 5 minutes. Finish at 400F (will
take 50 minutes or more)
98% Rustic
1) Same ingredients above, except 460 grams water in dough
2) Knead until glossy and hanging on dough hook - about 30 minutes on
Kitchen Aid speed 8
3) Shape and let rise in oiled 10 inch spring form ring, one hour or until
doubled.
4) Bake at 400F (with five minutes steam) until rich brown - about 70 minutes.
Phillip R. Seitz
artifact@erols.com