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In this chapter we are looking at the basics of how sourdough ferments.
For that we will first look at enzymatic reactions
that happen in your flour. These reactions are induced
the moment you add water to your flour. They are also
the basis that trigger the fermentation process. To understand
the fermentation process we are having a closer look at the involved
yeast and bacterial microorganisms.
In this chapter, we will cover the basics of how sourdough ferments.
First, we will look at the enzymatic reactions that take place
in your flour the moment you add water, triggering the fermentation
process. Then, in order to better understand this process, we will
learn more about the yeast and bacterial microorganisms involved.
\begin{figure}[!htb]
\includegraphics[width=\textwidth]{infographic-enzymes}
@@ -14,195 +12,207 @@ yeast and bacterial microorganisms.
\section{Enzymatic reactions}
When mixing flour and water several enzymatic reactions
start. A plant produces seeds to reproduce. The seed
contains all the nutrients a new plant needs to sprout.
While the seed is dry the seed is in hibernation mode. It
can be sometimes be stored for several years. The moment water is added
to the seed the sprouting process starts. The seed turns
into a germ. The stored nutrients have to be converted
into something that the germ can use. The catalyst for these
reactions is water. The first roots can be produced with the stored nutrients.
Furthermore the seed typically contains the first leaves
of the plant. The first leaves are built to start the photosynthesis
process. This is the plants' engine. With energy from photosynthesis
the plant can keep growing more roots. This way more water
and nutrients can be accessed from the soil. The extended
nutrients allow the plant to form more leaves and thus
increase the photosynthetic activity.
To understand the many enzymatic reactions that take place when flour
and water are mixed, we must first understand seeds and their role in
the lifecycle of wheat and other grains.
Of course a ground flour can no longer sprout. But the enzymes
that trigger this process are still present. That's why it's
important to not mill the grains at a too high temperature.
This could possibly damage some of the enzymes. Normally
the seed of the flour shields the germ against pathogens initially.
However as we grind the flour the contents of the seed
are exposed. This is ideal for our sourdough microorganisms.
The yeast can be considered a saprotrophic fungus.
They can't prepare their own food. As the enzymes start
to be activated more and more food becomes available
for the yeast and bacteria.
Seeds are the primary means by which many plants, including wheat,
reproduce. Each seed contains the embryo of another plant, and must
therefore contain all the nutrients that new plant requires to grow.
The two main enzymes for bread making are amylase and protease.
Understanding their role is a key puzzle piece to be able
to make better tasting bread at home.
When the seed is dry, it is in hibernation mode and can sometimes be
stored for several years. The moment it comes into contact with water,
however, it begins to sprout. The seed turns into a germ, requiring the
stored nutrients to be converted into something the plant can use while
it grows. The catalyst that makes the associated reactions possible is water.
The seed typically contains the first prototypical leaves of the plant,
and can put down roots using the stored nutrients inside. Once those leaves
break through the soil and come into contact with the sunlight above, they
begin to photosynthesize. This process is the plant's engine, and with the
energy photosynthesis produces, the plant can continue to grow more roots,
enabling it to access additional nutrients from the soil. These additional
nutrients allow the plant to grow more leaves, increasing its photosynthetic
activity so that it can thrive in its new environment.
Of course, a ground flour can no longer sprout. But the enzymes that
trigger this process are still present. That's why it's important not to
mill grains at too high a temperature, as doing so could damage some of
these enzymes.
Normally, the grain seed shields the germ against pathogens. However, as the
grain is ground into flour, the contents of the seed are exposed. This is ideal
for our sourdough microorganisms.
% I removed the line referencing yeast as a saprotrophic fungus since you
% cover this later on in the chapter and removing that helps the text to
% flow more smoothly.
Neither the yeast nor the bacteria can prepare their own food. However, as
the enzymes are activated, the food they need becomes available, allowing them
to feed and multiply.
The two main enzymes involved in this process are \textit{amylase} and
\textit{protease}. For reasons that will soon be made clear, they are of the
utmost importance to the home baker and their role in the making of sourdough
is a key puzzle piece to making better-tasting bread.
\subsection{Amylase}
Sometimes when you chew on a potato or a piece of bread
for a prolonged period of time you will notice a bit of sweetness
arising in your mouth. That's because your salivary glands
are also producing amylase. Amylase breaks down complex
starch molecules into easier digestible sugars. The germ
needs this in order to be able to produce more plant matter.
Your body needs this in order to start the digesting process.
Normally your microorganisms can't consume the freed maltose molecules
as they are hidden in the germ. But as we ground the flour
a feeding frenzy starts. Generally the warmer the temperature
the faster this reaction happens. That's why a long fermentation
is a key factor to make great bread. It takes time
for your amylase to break down most of the starch. Furthermore
not all sugars are consumed by the yeast. Some remain and
are responsible for enhanced browning during the baking
process.
Sometimes, when you chew on a potato or a piece of bread for a long period
of time, you'll perceive a sweet flavor on your tongue. That's because your
salivary glands produce amylase. Amylase breaks down complex starch molecules
into easily-digestible sugars. The germ needs this to produce more plant
matter, and your body needs this to kick-start the digestive process. Normally,
the microorganisms on the surface of the grain can't consume the freed maltose
molecules, which remain hidden inside the germ. But as we grind the flour, a
feeding frenzy takes place. Generally, the warmer the temperature, the faster
this reaction occurs. That's why a long fermentation is key to making great
bread. It takes time for the amylase to break down most of the starch into
simple sugars, which are not only consumed by the yeast but are also essential
to the \textit{Maillard reaction}, responsible for enhanced browning during the
baking process.
If you are a hobby brewer you will know that it's
important to keep your brew on certain temperatures for a
while to allow the different amylases to convert starches
into sugar \cite{beer+amylase}. There's a test frequently used by brewers
to determine that all the starches have been converted.
It's called the Iodine starch test. You take a bit of your brew
and then add a bit of iodine. If the color is blue/black
you know that you still have starches left that haven't been
converted by amylases yet. I wonder if such a test would work
for a bread dough as well? Now industrial bakeries
that use yeast to make speed doughs in a short period of
time face this issue. Their approach is to add malted
flour to the dough mix. The malted flour contains a lot
of enzymes and will thus help to have a faster fermentation
period. Check the packaging of the breads that you bought,
if you find {\it malt} in the list of ingredients chances
are that this strategy has been used. There are two categories
of malts. You have enzymatically active malt and inactive
malt. The active malt hasn't been heated to above 70°C
when the amylases start to degrade under heat. The inactive
malt has been heated to higher temperatures and thus
has no impact on your flour.
If you're a hobby brewer, you'll know that it's important to keep your beer at
certain temperatures to allow the different amylases to convert the contained
starches into sugar \cite{beer+amylase}. This process is so important that
there's a frequently used test to determine whether or not all the starches
have been converted.
This test, called the \textit{Iodine Starch Test}, involves mixing iodine into
a sample of your brew and checking the color. If it's blue or black, you know
you still have unconverted starches. I wonder if such a test would also work
for bread dough?
Industrial bakers that add especially active yeast to produce bread in a short
period of time face a similar issue. Their approach is to add malted flour to
the dough. The malted flour contains many enzymes and thus speeds up the
fermentation process. The next time you're at the supermarket, check the
packaging of the bread you buy. If you find {\it malt} in the list of
ingredients, chances are this strategy was used.
Note that there are actually two categories of malt. One is {\it enzymatically
active malt}, which has not been heated to above 70°C, where the amylases begin
to degrade. The other is {\it inactive malt}, which has been heated to higher
temperatures and thus has no impact on your flour.
\subsection{Protease}
The second very important enzyme is the protease. Proteases
break down proteins into smaller proteins or amino acids.
Gluten for instance is a storage protein built by wheat.
The gluten is broken down and converted the moment the
seed starts to sprout. That's because the seed needs
smaller amino acids to build the roots and other plant material.
If you ever try to make a wheat based dough and just keep
it for several days at room temperature you will notice
how your gluten network starts to break down. The dough
no longer holds together. You can just fully tear it apart.
I have had this happen to me when I was trying to make
doughs directly with dried sourdough starter. The fermentation
speed was so low that it took 3-4 days for the dough
to be ready. The root cause for this issue is the protease.
By adding water to the dough the protease was activated
and started to ready amino acids for the germ in order to be
able to sprout. Another interesting experiment that viusalises
the importance of protease is the following. Try to make a
fast dough within 1-2 hours. Simply use a large quantity
of dry yeast. Your dough will be leavened and increase in size.
Bake your dough and notice the crumb of your baked dough.
You will notice that the crumb is quite dense and not as
fluffy as it could be. That's because the protease enzyme
didn't have enough time to do its job. At the start
when kneading your dough is very elastic. It holds together
very well. Over the course of the fermentation process
your dough will become more extensible \cite{protease+enzyme+bread}.
Some of the gluten bonds start to naturally break
down due to the protease proteolysis. This makes it easier
for your dough to be inflated. That's why a long
fermentation process is important when you want to
achieve very fluffy and open crumbs with your sourdough
bread. Next to using great ingredients, the long and
slow fermentation is one of the main reasons why
Neapolitan pizza tastes so great. The soft and fluffy
edge of the pizza is achieved because of the protease
creating a very extensible easy to inflate dough. Because
the fermentation process is typically longer than 8
hours a flour with a higher gluten content is used. There
is more gluten that can be broken down by the protease.
By using a weaker flour you might end up with a dough
that's already broken down too much and will then tear
when trying to make a pizza pie. Traditionally the pizza
has probably been made with sourdough. In modern times
it is made with yeast as handling a yeast based
dough can be done easier on a larger scale. The dough
stays good for a longer period of time. If you were to use
sourdough you might have a window of 30-90 minutes when
your dough is perfect. Afterwards the dough might
start to deteriorate because of bacteria breaking
down the gluten network too much.
Just as amylase breaks starches down into simple sugars, protease breaks
complex proteins down into simpler proteins and amino acids. Because wheat
contains gluten, a protein that's essential to the structure of bread,
protease necessarily plays a crucial role in the baking of sourdough.
Since the grain seeds require smaller amino acids to build roots and other
plant materials, the gluten in those seeds will begin to break down the moment
they sprout, and since adding water to flour activates those same enzymes,
the same process occurs in bread dough.
If you've ever tried to make a wheat-based dough and kept it at room
temperature for several days, you'll have discovered for yourself that the
gluten network breaks down so that the dough can no longer hold together. Once
this happens, the dough easily tears, holds no structure, and is no
longer suitable for baking bread.
This happened to me once when I tried to make sourdough directly from a dried
starter. At three to four days, the fermentation speed was so slow that the
gluten network broke down. The root cause for this issue was protease.
By adding water to your dough, you activate the protease, and this gets to work
in readying amino acids for the germ.
Here's another interesting experiment you can try to better visualize the
importance of protease: Make a fast-proofing dough using a large quantity
of active dry yeast. In one to two hours, your dough should have leavened and
increased in size. Bake it, then examine the crumb structure. You should see
that it's quite dense and nowhere near as fluffy as it could have been. That's
because the protease enzyme wasn't given enough time to do its job.
At the start, while kneading, a dough becomes elastic and holds together very
well. As that dough ferments, however, it becomes more loose and extensible
\cite{protease+enzyme+bread}. This is because some of the gluten bonds have
been broken down naturally by the protease through a process known as
\textit{proteolysis}. This is what makes it easier for the yeast to inflate the
dough, and it's why a long fermentation process is critical when you want to
achieve a fluffy, open crumb with your sourdough bread.
Aside from using great ingredients, the slow fermentation process is one of the
main reasons Neapolitan pizza tastes so great; because the protease creates an
extensible, easy-to-inflate dough, a soft and airy edge is achieved.
Because the fermentation process typically takes longer than eight hours, a
flour with a higher gluten content should be used. This gives the dough more
time to be broken down by the protease without negatively affecting its
elasticity. If you were to use a weaker flour, you might end up with a dough
that's broken down so much that it tears during stretching, making it
impossible, for example, to shape it into a pizza pie.
Traditionally, pizza has been made with sourdough, but in modern times it is
made with active dry yeast, as the dough stays good for a longer period of time
and is much easier to handle on a commercial scale. If you were to use
sourdough, you might have a window of thirty to ninety minutes before the dough
begins to deteriorate, both because of the protease acting for a longer period
of time and the byproducts of bacteria, which we'll discuss in more detail later
in this chapter.
\subsection{Improving enzymatic activity}
As explained previously malt is a common trick used
to speed up enzymatic activity. I personally prefer
to avoid malt in most of my recipes. Instead I use
a trick I observed when making whole wheat doughs.
No matter what I tried I could never achieve baking
a whole wheat bread with the desired crust and crumb
texture I was looking for. My doughs would tend to
overferment relatively quickly. When using a flower
with a similar amount of gluten that didn't contain
bran and other outer parts of the grain my doughs turned
out great. I was utilizing an extended autolyse.
That's a fancy word for just mixing flour and water in
advance and letting that mixture sit. Most recipes
call for it as the help to make a dough that has already
started to break down by enzymes. In general it's a great
idea but at the same time you can just reduce the amount
of leavening agent you use. This way the same biochemical
reactions happen and you don't have to mix your dough
several times. My whole wheat game drastically improved
when I stopped using the autolysis. It makes sense if I
think about it now. The first parts of the seed that
are in contact with water are the outer parts. Water
will slowly enter the center parts of the grain. The
moment the seed starts to sprout it needs to outcompete
other nearby seeds. Furthermore it also directly becomes
exposed to other animals and potential hazardous bacteria
and fungi. To accelerate this process most of the enzymes
of the grain are in the outer parts of the hull. They
are being activated first (source needed). So by just
adding a little bit of whole flour to your dough you
will improve enzymatic activity of your dough. That's
why most of my plain flour doughs typically contain
at least 10-20 percent whole wheat flour.
As explained previously, malt is a common trick used to speed up enzymatic
activity. Personally, however, I prefer to avoid malt and instead use a
trick I learned while making whole-wheat breads.
When I first started making whole-wheat bread, I could never achieve the
crust, crumb, or texture I desired no matter what I tried. Instead, my dough
tended to overferment rather quickly. When using a white flour with a similar
gluten content, however, my bread always turned out great.
At the time, I utilized an extended autolyse, which is just a fancy word for
mixing flour and water in advance and then letting the mixture sit. Most
recipes call for it as the process gives the dough an enzymatic head start, and
in general it's a great idea. However, as an equally effective alternative,
you could simply reduce the amount of leavening agent used (in the case of
sourdough, this would be your starter). This would allow the same biochemical
reactions to occur at roughly the same rate without requiring you to mix your
dough several times. My whole wheat game improved dramatically after I stopped
autolysing my doughs.
Now that I've had time to think about it, the result I observed makes sense.
In nature, the outer parts of the seed come into contact with water first, and
only after penetrating this barrier would the water slowly find its way to the
center of the grain. The seed needs to sprout first to outcompete other nearby
seeds, requiring water to enter quickly. Yet the seed must also defend itself
against animals and potentially hazardous bacteria and fungi, requiring some
barrier to protect the embryo inside. A way for the plant to achieve both goals
would be for most of the enzymes to exist in the outer parts of the hull. As a
result, they are activated first (source needed). Therefore, by just adding a
little bit of whole flour to your dough, you should be able to significantly
improve the enzymatic activity of your dough. That's why, for plain white flour
doughs, I usually add 10\textendash20\% whole-wheat flour.
\begin{figure}
\includegraphics[width=\textwidth]{whole-wheat-crumb}
\caption{A whole wheat sourdough bread}
\caption{A whole-wheat sourdough bread}
\label{whole-wheat-crumb}
\end{figure}
By understanding the 2 key enzymes amylase and protease
you will better be able to understand how to make a
dough to your liking. Would you like a dough a softer
or stiffer crumb? Would you like to achieve a darker crust?
Would you like to reduce the amount of gluten in your
final bread? These are all factors you can influence
by adjusting the speed of fermentation.
By understanding the two key enzymes \textit{amylase} and \textit{protease}, you
will be better equipped to make bread to your liking. Do you prefer a softer
or stiffer crumb? Do you desire a lighter or darker crust? Do you wish to reduce
the amount of gluten in your final bread? These are all factors that you can
tweak just by adjusting the speed of your dough's fermentation.
\section{Yeast}
Yeasts are single celled microorganisms that are part of
the fungus kingdom. Yeast spores that are hundreds
of million years old have been identified by scientists.
There is a wide variety of species and so far around 1500
different species have been recognized. Yeasts are not creating
a mycelium network like mold does for instance
\cite{molecular+mechanisms+yeast}.
% Yeast is both the singular and plural form of the word unless you're
% specifically referencing a plural number of varieties or types, in which case
% "yeasts" would be correct.
Yeast are single celled microorganisms belonging to the fungi kingdom, and
spores that are hundreds of millions of years old have been identified by
scientists. There are a wide variety of species: So far, about 1,500 have been
identified. Unlike other members of the fungi kingdom, such as mold, yeast do
not ordinarily create a mycelium network \cite{molecular+mechanisms+yeast}
\footnote{For one interesting exception, skip ahead to the end of this
section.}.
\begin{figure}[!htb]
\centering
@@ -211,106 +221,105 @@ a mycelium network like mold does for instance
\label{saccharomyces-cerevisiae-microscope}
\end{figure}
Yeast are saprotrophic fungi. This means that they do not produce their own
food, but instead rely on external sources that they can decompose and break
down into compounds that are more easily metabolized.
Yeasts are saprotrophic fungi. This means they are not
producing their own food. They rely on external food sources
which they decompose and break down. For yeasts
carbohydrates and broken down to carbon dioxide and
alcohols. The products of this fermentation process
have been used for thousands of years when making
bread or alcoholic beverages. Yeasts can grow
in both aerobic and anaerobic conditions. When oxygen
is present the yeast almost completely produces
carbon dioxide and water. When no oxygen is present
the yeast starts switches its metabolism. The
yeast starts to produce alcoholic compounds \cite{effects+oxygen+yeast+growth}.
The temperatures at which the yeast grows vary. Some
yeasts such as {\it Leucosporidium frigidum} grows
best at temperatures between -2°C up to 20°C. Other
yeast grows better at higher temperatures. The warmer
it is the faster the yeast's metabolism works. The yeast
that you cultivate in your sourdough starter works best
at the temperatures where the grain was grown and at
the point when it was harvested. So if you are from a
cooler place and cultivate a sourdough starter from
a nordic rye variety, then chances are your yeast
prefers this colder environment. As an example
beer makers discovered that a beneficial yeast lives
in the cold caves around the city of Pilsen, Czech Republic.
This yeast has produced excellent tasting beers at
lower temperatures. Varieties of these strains
are now used to make popular lager beers.
Yeast breaks down carbohydrates into carbon dioxide and alcohol in what we today
refer to as the fermentation process. This process has been known for thousands
of years and has been used since ancient times for the making of bread as well
as alcoholic beverages.
Yeasts in general are very common in the environment.
They can be found on cereal grains, fruits, other plants
in the soil and also in your gut. Very little is known
about the ecology of why yeasts we use for baking
are cultivating the leaves of the plants. The plants
are protected via the cell walls and hardly any
fungi and other bacteria can penetrate. Some fungi and
bacteria are producing enzymes that are able
to break down the cell walls and infect the plant.
There are fungi and bacteria that live within the plant
without causing any distress. These are known as {\it endophytes}.
They are not damaging the plant per se. In fact they are
living in a symbiotic relationship with the host. They
help the plant to protect itself from additional pathogens
that might enter through the leaves of the plant. They
help with water stress, heat stress and nutrient availability.
In exchange for the service they receive carbon for energy
from the plant host. They are not always strictly mutualistic though.
Sometimes under stress conditions they can become pathogens
on their own \cite{endophytes+in+plants} and decay begin
decaying the plant.
Yeast can grow and multiply under both aerobic and anaerobic conditions. When
oxygen is present, they produce carbon dioxide and water almost exclusively.
When oxygen is not present, their metabolism changes to produce alcoholic
compounds \cite{effects+oxygen+yeast+growth}.
The yeasts we use for baking are
living as as epiphytes on the plant. Compared to
the previously mentioned endophytes they are not
breaching the walls of the cells. Most of them
receive nutrients from rain water, the air or other animals.
These sources also include honeydew produced
by aphids. Pollen that lands on the leaf's surface
is an additional source of food. Interestingly
though when you remove that external food source,
you still find a large variety of epiphytic fungi
and bacteria on the plant's surface. The food
for them is coming directly from the plant it seems.
Some research has shown that the plants are
on purpose releasing some compounds such as sugars,
organic acids, amino acids, some methanol and various
salts via the surface. These nutrients would
then attract the epiphytes to live on the surface.
The plants benefit from enhanced protection against
mold and other pathogens. It is in the best interest
of the epiphytes to keep the plants alive
as long as possible \cite{leaf+surface+sugars+epiphytes}.
More and more research is conducted on using yeasts
as a biocontrol agents to protect plants. These bio-agents
would be food-safe as yeasts are generally considered save.
The yeasts would start to grow on the leaves on the plant
and essentially shield the plants from other molds. This
could be a game changer for wineyeards suffering from mildew.
This could also be helpful to shield the plant against the
psychoactive ergot fungus. The ergot fungus likes to grow
in more humid colder environments and poses a huge
problem to rye farmers. The fungus parasites the plant
and infects it. Consumption of ergot is not recommended
as it is highly toxic to the liver. That's why lawmakers
have recently reduced the amount of allowed ergot contamination
in rye flour. Another interesting experiment from Italian scientists
visualized how important yeasts could be when protecting
plants. They added tiny incisions into some of the grapes.
They would then infect some of the damaged surfaces with
mold. The other wounds they infected with some of the 150
different wild yeast strains isolated from the leaves plus
the mold. When mixing the mold with the yeast the grape
The temperatures at which yeast grows varies. Some yeasts, such as
{\it Leucosporidium frigidum}, do best at temperatures ranging from -2°C to
20°C, while others prefer higher temperatures. In general, the warmer the
environment, the faster the yeast's metabolism. The variety of yeast
that you cultivate in your sourdough starter should work best within the range
of temperatures where the grain was grown and harvested. So, if you are from a
cooler place and cultivate a sourdough starter from a nordic rye variety,
chances are your yeast will prefer a colder environment.
As an example, beer makers discovered a beneficial yeast living in the cold
caves around the city of Pilsen, Czech Republic. This yeast has since become
known for producing excellent beers at lower temperatures and varieties of
these strains are now used for brewing popular lagers.
Yeasts in general are very common organisms. They can be found on cereal
grains, fruits, and many other plants in the soil. They can even be found
inside your gut! As it happens, the types of yeast we use for baking are
cultivated on the leaves of plants, though very little is known about the
ecology involved.
Plants are protected by thick cell walls that few fungi or bacteria can
penetrate. However, there are some species that produce enzymes capable of
breaking down those cell walls so they can infect the plant.
Some fungi and bacteria live inside plants without causing them any distress.
These are known as {\it endophytes}. Not only do they \textit{not} damage their
host, they actually live in a symbiotic relationship, helping the plants in
which they dwell to protect themselves from other pathogens that might also
come to infect them through their leaves. In addition to this protection, they
also help with water and heat stress, as well as the availability of nutrients.
In exchange for their service to their host plants, these fungi and bacteria
receive carbon for energy.
However, the relationship between endophyte and plant is not always mutually
beneficial, and sometimes, under stress, they become invasive pathogens and
ultimately cause their host to decay \cite{endophytes+in+plants}.
There are other microorganisms that, unlike endophytes, do not penetrate cell
walls but instead live on the plant's surface and receive nutrients from rain
water, the air, or other animals. Some even feed on the honeydew produced by
aphids or the pollen that lands on the surface of the leaves. Such organisms
are called \textit{epiphytes}, and included among them are the types of yeast
we use for baking.
Interestingly, when you remove external food sources, a large number of
epiphytic fungi and bacteria can still be found on the plant's surface,
suggesting that they must somehow be feeding directly from the plant.
Indeed, there is some research indicating that some plants intentionally release
compounds such as sugars, organic and amino acids, methanol, and various
salts along the surface. These nutrients would then attract the epiphytes that
live on the plant's surface.
Epiphytes are advantageous to a plant's survival, as they are provided with
enhanced protection against mold and other pathogens. Indeed, it is in the
best interest of the epiphytes to keep their host plants alive for as long as
possible \cite{leaf+surface+sugars+epiphytes}.
More research is conducted every day in ways that yeasts can be used as
biocontrol agents to protect plants, the advantage being that these bio-agents
would be food-safe as the relevant strains of yeast are generally considered
harmless to humans. The yeasts would grow and multiply on the leaves,
esentially shielding them from other types of mold. This could be a potential
game changer for vineyards that suffer from mildew.
Such bio-agents could also be used to shield plants against the psychoactive
ergot fungus, which likes to grow in colder, more humid environments and
poses a significant problem for rye farmers. Because it infects the grain
and makes it unfit for consumption due to its high toxicity to the liver,
lawmakers have recently reduced the amount of allowed ergot contamination in
rye flour.
There is another interesting experiment performed by Italian scientists that
shows how crucial yeasts could be in protecting our crops. First, they made
tiny incisions into some of the grapes on a vine. Then, they infected the
wounds with mold. Some incisions were only infected with mold. Others were also
innoculated with some of the 150 different wild yeast strains isolated from the
leaves. They found that when the wound was innoculated with yeast, the grape
sustained no significant damage \cite{yeasts+biocontrol+agent}.
In another experiment however scientists have shown
how the brewer's yeast became an aggressive pathogen to wine plants.
Initially the yeast lived in symbiosis with the plant. After the grapevine
sustained damages the yeast became opportunistic and started to
attack the plant event producing hyphae to deeply
penetrate the plants tissue.
Intriguingly, there was also an experiment performed that showed how brewer's
yeast could function as an aggressive pathogen to grape vines. Initially, the
yeast lived in symbiosis with the plants, but after the vines sustained heavy
damage, the yeast became opportunistic and started to attack, even going so far
as to produce hyphae, the mycellium network normally associated with a fungus,
so that they could penetrate the tissue of the plants.
\section{Bacteria}

11
book/intro/acknowledgements.tex
View File

@@ -1,14 +1,13 @@
This book would not have been possible without the help of the community.
All the donations have made it possible that I was able to take
some time off from my job and YouTube to write this free book.
By providing this information free to everyone we can
enable more people around the world to bake delicious
sourdough bread at home. Thank you very much!\\
Because of the donations received, I have been able to take time off from
my job and from YouTube to write it. By providing this information free
of charge, we can help more people around the world bake delicious sourdough
bread at home. Thank you very much!\\
\begin{filecontents}{supporters.csv}
\end{filecontents}
{\large All supporters sorted by name}
{\large All supporters, sorted by name:}
\pgfplotstableset{
begin table=\begin{longtable},