Saturday, 4 February 2012

Questions about sourness

Vitalyi, a fellow home-baker-turned-pro in Yekaterinburg, writes with some questions about leaven refreshment and sourness:

According to our experience we use 3hrs for fermentation and 2hrs 30mins
for final prove at 25 celcius. We have found that the shorter final proof, the
less oven spring is. When the final proof longs 2hrs, the volume of the loaf is
visibly less. Maybe there is another reason for the phenomenon.

My Reply:
Volume is greatest when the dough develops the right combination of strength (to trap gas) and elasticity (to stretch without tearing). When the
proof is too short, the dough is strong without being elastic and the
strength prevents expansion. This can cause bursting and tearing. When
the proof is too long the dough is elastic but strength lessens, and it
cannot hold so much gas - so volume suffers. An overprooved loaf tends
to flatten a little and may tear as it does so. But lots of things
contribute to dough development, not just the length of the final proof;
these include the ripeness of the leaven, the stiffness of the dough,
the temperature of the dough and the length of the initial ferment.


Is it crucial for the sourness of the final loaf that the starter should
be refreshed just before the mixing and kneading of the dough?

My reply:
This depends what you mean by 'just before'. The crucial factor is that the
the leaven should be correctly developed when it is added to the final
dough. What counts as 'correctly developed' depends on how you want your
bread to turn out. There are lots of ways to create sourness; in
general longer, cooler, stiffer ferments favour lacto-bacillic
fermentation (and thus result in more sourness), whilst short, soft,
warm ferments favour yeast fermentation (resulting in more gas
production). The trick is to balance flavour with texture and volume -
sourness is produced by acid; too much acid can harm the strength of the
dough. In my experience, 25 Celsius creates a good balance for a final
dough. I refresh my leaven twice before using it - the first time it is
warm (28 celsius or so), liquid (100% hydration) and short (4-6 hours),
the second is cool (less than 18 celsius), stiff (64% hydration for my
wholemeal wheat leaven) and long (12-16 hours, overnight). The first
creates lively yeasts, the second boosts the lacto-bacillae population.

Our wheat starter is maintained for more than half a year. We keep it
normally in refrigerator. Its water content is 100% and we feed it before
backing with 1:1 mixture of water and wholewheat flour, the weight of the
starter and the weight of the fresh dough being equal. Could you comment this
technique? How does it impact on the sourness of the final wheat bread? And why
do you use wholemeal rye leaven for the wheat bread? Is there any difference
between the words “starter” and “leaven”?

My reply:
100% hydration is a good compromise of the many factors affecting the action  of a starter. As a home-baker I maintained only one rye starter for
many years, and that was 100% hydration. I'm not sure that I have
understood the amount of starter that you use for refreshing - I use
20-40% of the flour weight, depending on how long I want to leave it for
and how warm the day is, so I might make 1.2kg of leaven using 500g
wholegrain rye flour, 500g water and 200g rye starter. See my above
comments about refreshing for some ideas about how different feeding
regimes impact on the final bread.

There isn't really any difference between 'starter' and 'leaven',
but I tend to use 'chef' for the perpetual culture that I keep in the
fridge, 'starter' for the first refreshment, and 'leaven' for the final
refreshment that gets used in the final dough.

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