Saturday, April 28, 2012
Understanding Leaveners - Yeast, Baking Soda, and Egg Whites
8:22 PM | 
Posted by
commiskaze |
To the home baker, this is often a
conundrum “Shit, I ran out of baking soda what else can I use?”
We have all been there, and this is all a matter of understanding
what is actually going on inside your recipe. Some of this believe it
or not is grade school science, and I am here simply to reiterate
something that seems elaborate but is not. Leaveners are the things
that make our baked goods rise, in short.
Fundamentally, all of these things
achieve one thing: they produce (usually carbon dioxide, or
incorporate gas.) This is can be achieved three different ways:
microbial, chemical, or mechanical.
Microbial
Microbial leavening is achieved through
yeasts. The same things that produce two of our favourite things:
alcohol, and bread. This is fermentation. Yeast leavening can be
complicated by going down a baking aisle, and seeing fast acting
yeast, cake yeast, brewers yeast, sourdough etc. I will delve into
that more complicated bit after. What is important is to understand
that yeasts eat sugars. These can be sugars from starches
(carbohydrates), table sugar, honey, etc. Some of these sugars are
more digestible then others, but for our purposes, that is not
important. When a yeast eats a sugar it farts, vomits, and procreates
(much like a frat house). It farts carbon dioxide, vomits alcohol,
and produces more yeast.
If left in a liquid with a sugar, it
will produce alcohol and the carbon dioxide will escape. This is how
we get beer. Bread is much like beer, and bread dough is even mildly
alcoholic. The different is that when we knead a dough together we
create gluten, and this gluten traps the carbon dioxide which causes
the bread to “rise,” much like blowing up a balloon. When the
bread is baked, the alcohol is burned off.
This brings us to the next topic -types
of yeast. There are different strains of yeast, some are better are
producing alcohol, some better at producing carbon dioxide. There are
also wild yeasts (yes they watch you while you are sleeping). For
baking purposes we are interested in the ones that produce carbon
dioxide. Now we have a selection to choose from, and without getting
into all of them it fundamentally comes down to how fast they wake up
and do their thing. Think normal yeast as sleepy factory workers, and
thing of super active yeast as the Incredible Hulk. Our Hulk is the
same as our Average Joe yeast, except he is packed with beneficial
nutrients that wake him up and get him going faster. If we gave our
factory yeasts Red Bull (ie yeast nutrients) the same thing would
happen.
Having a Hulk yeast is not always a
beneficial thing. This is an important principle in bread making.
Time equals Taste. The longer your bread ferments, the more flavour
it will have. This is the reason store bought white bread tastes so
different than a sourdough (which we will get into soon).
So hypothetically, we want a flavourful
bread but all we have is the Hulk. How can we achieve this?
A big factor in microbial action, and
fermentation is temperature. The higher the temperature (that they
can survive happily,) the faster they will work. The reverse is also
true. If we put our dough the fridge, it will take longer to rise,
and produce more flavour. If we need it to rise faster we put it in a
warmer spot in the house. Simple non?
So what then is sourdough, and why is
it so tasty. Sourdough is the homeless yeast, the teenager, or the
Iggy Pop, it is wild and fairly untamed. It is produced by creating a
substance that will attract the ambient yeasts living in your house,
and cause them to colonize it. This is usually accomplished by a
mixture of flour and water, left out in the open for several days
until it either molds (in which case it was colonised by other
microbials,) or begins to bubble and ferment. When it begins to do
this you basically have another pet. You have to feed it, nourish it,
and give it a place to sleep. I will not go too in depth to the art
of sourdough. Because this yeast really does not “want” to work,
the dough takes a long time to ferment, and produces a very fermented
flavour. This flavour is unique because more then likely this yeast
is unique to your specific area. This is why San Francisco sourdoughs
are so popular, they produce a different strain of yeast! Not to say
“Your House” sourdoughs cant be better.
To add to the confusion, often you will
see the word starter, biga, poolish, or sponge. These are all
basically the same thing, they are “pre-ferments”, it is a middle
of the road for flavour. How this is achieved it by starting a
“dough” ahead of time, letting the yeasts age and establish
themselves and then using this “dough” to ferment your actual
dough. If we wanted to make a pre-ferment we would take a small
portion of yeasts, and water out of our recipe, put our yeasts in
that, and let it do its thing overnight on the counter or in the
fridge. Where all these strange names differ is in what ratio of
flour to water that is in the pre-ferment. Some bakers prefer it more
liquid, some prefer it more dough-like in consistency. Another way to
achieve this is to make your initial dough, and save a tiny piece for
the next batch of dough; they downside however is the reliability.
The things we can take away from this
is: Yeasts produce carbon dioxide, that carbon dioxide gets trapped
in our dough and causes it to rise, the longer it takes to rise the
more flavour it will have.
Chemical
Chemical leavening is usually achieved
by using either baking soda or baking powder. I find the easiest way
to explain this is to go back to a grade school science fair where
without a doubt, someone made a “volcano.” If you remember the
reaction was created by taking baking soda, and vinegar putting them
together and watching the mess ensue. This is what happens when you
mix an acid (vinegar), and a base (sodium bicarbonate) This is
exactly what happens when you use them in baking. If a recipe calls
for baking soda, it will always have an acid accompanying it. This is
usually lemon juice, buttermilk or cream of tartar (which is actually
tartaric acid). What happens is our volcano reaction happens in our
mixture creating carbon dioxide which is trapped and baked. This can
be accomplished using baking soda and any acid you can think of (well
as long as it is food friendly). The chemical responsible for this is
sodium bicarbonate.
The difference between baking soda, and
baking powder is that baking powder contains both sodium bicarbonate,
and tartaric acid (cream of tartar). It often uses an inert starch as
a drying agent as well.
So we have a recipe that calls for
baking powder, but all we have is baking soda. How can we create our
own baking powder?
1 part baking soda
1 part cornstarch
2 part cream of tartar
Ok, but I am out of cream of tartar,
and cornstarch. What else can I use? If we require one teaspoon of
baking powder we can use these substitutions:
1/2 tsp baking soda +1/2 cup
buttermilk, yogurt, or soured milk (1/2 cup milk + 1 1/2 tsp
vinegar/lemon juice)
1/2 tsp baking soda +1 1/2 tsp lemon
juice, or vinegar
1/2 tsp baking soda + 1/3 tsp citric
acid
More often then not you will use 1 tsp
of baking powder per 1 cup of flour. When we substitute using liquid
you must also adjust your recipe by taking out other liquids. The
problem with substitutions is although some can be straightforward
others can change the texture/flavour of the recipe. Technically it
is an exact science, realistically not so much.
There are also single acting, and
double acting baking powders. Single acting only activates when
applied with heat (ie being baked), whereas double acting will react
at room temperature AND when applied with heat. Also note that self
rising flour is normal flour with the addition of baking powder. To
make your own take normal flour and add 1 1/4 tsp of baking powder,
and a 1/4 tsp of salt.
What we can take away from chemical
leavening is this: Baking soda is a base, when this base is combined
with acid it will produce carbon dioxide and cause our recipe to rise
(with the application of heat), baking powder is baking soda combined
with acid already. Now that you understand the “why” it should be
much easier to understand what is going on in your recipes, and how
to substitute the various ingredients.
Mechanical
Mechanically leavening something is
probably the simplest of all processes. We use mechanical movement to
introduce air, and then gently heat it to cement it together. Mainly
what we are talking about are egg whites. Whipped egg whites are
responsible for many delicacies such as souffles, macarons,
meringues, sponge cake, etc. Cream is not generally baked while
whipped, however ice cream is an example where air is whipped into
the ice cream mixture which increases its volume and then frozen. We
will concentrate on egg whites.
Without going too scientific (if you
wish to, buy On Food and Cooking by Harold Mcgee) when egg whites are
whipped two chemicals in the egg whites are attracted to each other
and form the framework through molecular bonds. If baked right away
(usually very low gentle heat,) this framework is solidified, and
leaves us with a light airy product. Although it is not exactly that
simple, the same forces that create this network can also become too
tightly bonded and cause the whites to collapse. To further
complicate things whites have water, and if contaminated by yolk,
fat. Both of these things will have a negative effect on the end
product, and work against your desired results.
Commonly it is advised both most French
pastry chefs that in order to get the best egg whites, the eggs must
be older, room temperature and aged. Harold McGee notes that your
eggs should be in a chilled bowl, and if needed a tiny bit of acid
added to them -1/2 tsp cream of tar tar. This is kind of
contradictory and unfortunately I do not have an answer. As eggs age,
they actually become less acidic, and warm eggs have a harder time
bonding together. Take what you will from that, I am not going to
argue with neither a Pastry chef, nor the Godfather of food science.
One thing that sounds like an old wives
tale which does have scientific merit, if the belief that a copper
bowl should be used when whipping eggs. This is true.
“It turns out that along with a few other metals, copper has the useful tendency to form extremely tight bonds with reactive sulphur groups: so tight that the sulphur is essentially preventing from reacting with anything else. So the presence of copper in foaming eggs whites essentially eliminates the strongest kind of protein bond that can form, and makes it harder for the proteins to embrace each other too tightly.” On Food and Cooking, Harold McGee
In a nut shell, the copper makes it
very hard for the whites to collapse. McGee also notes that silver
has the same effect as copper (for those of us that can afford
silver, let alone copper bowls). I've only briefly touched on this
subject because it is either a very simple straightforward topic, or
a highly scientific one. My copy of On Food and Cooking, is currently
lent out, so perhaps ill post one on the science of it when I get it
back.
I hope this answers more questions,
then it makes. Hopefully never again will someone ask me about baking
soda substitutions, or at least I will have a place to steer them.
Cheers.
Labels:
Basic Techniques
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5 comments:
Very detailed and useful! Thanks for the effor! ;)
With mechanical leavening you said that you are "basically" referring to egg whites. I was hoping that you may know of a substitute for egg whites. I know I'm a dreamer but....
Very helpful! Thank you for the time. There are a LOT of words on the page though!
Thanks so much for writing that.. I was wondering if there was a way I could make a light bread without chemicals or bacteria :-)
So the question I have, I stopped using baking soda and baking powder. I have my own sourdough starter ready for use and works perfect in bread recipes. I am still working on cake and cookie recipes. How can I substitute both baking powder and baking soda for sourdough starter. Is there a ratio. I know sourdough can differ in taste per region and you don't want the recipe to be too tangy. Is there a way to substitute the chemical leaveners for sourdough or should I give up and try make my own recipes?
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