MY EDX CERTIFICATE ON SCIENTIFIC COOKING MOOC HARVARD

 Your final grade: 91%.

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THE BLOG

Here is a kind of diary for my final project.  The material (photos, videos, lectures, sites on the web etc) will be posted on this blog. The report is prepared for the course ''SCIENCE AND COOKING'' presented on the platform EDX from HARVARD UNIVERSITY in autumn 2013.

Bacteria Control

Bacteria Control

Sauerkraut is made by lactic acid bacteria that break sugar into lactic acid, carbon dioxide (CO2, soda gas) and a little amount of alcohol. Because cabbage contains water, sugar and many nutrients it is a perfect media for all types of bacteria to grow, some of them we try to avoid. Heat treatment will surely kill undesirable bacteria, but it also will kill lactic acid bacteria that we need, so this method does not apply here.
pH acidity of fresh cabbage is at around pH 7.0 which is at neutral point of acidity scale. This makes cabbage an ideal food for microorganisms as it contains water, sugar, proteins, minerals and all nutrients. We control bacterial growth using the following steps:

• Washing.
• Applying salt.
• Elimination of oxygen.

Washing. Cabbage is in a direct contact with soil which is loaded with all types of microorganisms. Most microorganisms are present on outside green leaves which are usually discarded. One gram of fresh cabbage may contain 250,000 bacteria and this number may grow to 1,000,000 during storage. So, the first step is to wash the cabbage well as this action removes plenty of microorganisms. If ingredients such as apples or carrots will be added, thy must be thoroughly washed as well.
Salt. Salt is needed for two reasons:

• To remove the cabbage juice and nutrients from each cell and make it available as food to lactic acid bacteria. Bacteria will not eat dry cabbage leaves, however, they will absorb filled with nutrients juice. Bacteria are like sponge, they don’t pick up the dry matter but will suck up anything wet.
• To keep other bacteria away. A moderate amount of salt does not bother sauerkraut bacteria (lactic acid), however, other bacteria types find such conditions intolerable.

As lactic acid bacteria start to produce slowly lactic acid, this becomes even worse for other bacteria types, as generally bacteria hate acid. Of course lactic acid bacteria are not bothered by moderate amounts of acid at all. This combination of salt and increasing amount of acid inhibits growth of other bacteria and makes sauerkraut more stable as the fermentation advances
To make high quality sauerkraut salt is applied at 2 – 2.5% in relation to the weight of the sliced cabbage. Decreasing salt levels will create quality problems, going below 1.5% will rot the cabbage. Spoilage bacteria will survive such a low salt level and will take over the process and will spoil the product.
Absence of Oxygen. When container as packed with cabbage all microorganisms start to compete for food. Salt inhibits some of them, but many others need oxygen to survive, for example molds. Eliminating oxygen is accomplished by a few methods:

• Packing container hard with shredded cabbage.
• Slicing cabbage thinner, this allows to pack more cabbage and disperse more air.
• Keeping cabbage submerged in brine (using weights).
• Using water channel fermented crocks or air lock glass jars.

Eliminating oxygen preserves vitamin C from oxidizing and losing its strength.
Fermented sauerkraut exhibits pH at around 3.5 and will keep in cool conditions for a very long time, as long as this pH level is maintained.

Effect of Fermentation Temperature

Effect of Fermentation Temperature

The best quality sauerkraut is produced at 65-72° F (18-22° C) temperatures. Temperatures 45.5° F (7.5° C) to 65° F (18° C) favor the growth and metabolism of L.mesenteroides. Temperatures higher than 72° F (22° C) favor the growth of Lactobacillus species. Generally, lower temperatures produce higher quality sauerkraut, although at 45.5° F (7.5° C) bacteria are growing so slow that the cabbage might need 6 months to complete fermentation. Higher temperatures produce sauerkraut in 7-10 days but of the lesser quality. This creates such a fast fermentation that some types of lactic acid bacteria don't grow at all and less reaction take place inside what results in a less complex flavor.

• Below 45.5° F (7.5° C) fermentation time is up to 6 months.
• At 65° F (18° C) fermentation time is 20 days.
• At 90-96° F (32-36° C) fermentation time is 10 days.

FERMENTATION - LACTIC ACID PATHWAY

BACTERIA AND SAUERKRAUT FERMENTATION

Sauerkraut Fermentation

Sauerkraut fermentation requires almost no work on the part of the operator. Cabbage contains enough lactic acid bacteria in order to ferment and produce sauerkraut with salt alone. In order to obtain product of the highest quality all those bacteria strains must ferment in a certain sequence. This happens naturally as long as sauerkraut is fermented around 65° F (18° C).

1. Leuconostoc mesenteroides - they are the smallest and start the fermentation first producing around 0.25 to 0.3% lactic acid. They are heterofermenters, this means that they produce different compounds such as lactic acid, acetic acid (vinegar), ethyl alcohol, carbon dioxide (soda gas) and mannitol. The last one is a bitter flavored compound which is metabolized later by Lactobacillus plantarum. All those acids, in combination with alcohol from aromatic esters, contribute to the characteristic flavor of the high quality sauerkraut. If the temperature is higher than 72° F (22° C) they might not grow and that would be detrimental to the flavor of sauerkraut. In about 2 days Leuconostoc mesenteroides will produce 0.3% lactic acid and this increased acidity will restrict its growth. Nevertheless, the enzymes it produced will continue to develop flavor.
2. Lactobacillus plantarum - this strain takes over the production of lactic acid from Leuconostoc mesenteroides and continues fermenting until an acidity level of 1.5 to 2% is achieved. L. plantarum will ferment at temperatures higher than 72° F (22° C) and it can grow at higher acidity levels. It will ferment at lower temperatures as well, albeit at much slower rate. Lactobacillus plantarum is the most popular lactic acid bacteria strain and it ferments sauerkraut, pickles, cheese and even meat. This bacteria is a homofermenter what means that it produces one compound only. It consumes sugar and produces lactic acid which imparts acidic taste to fermented food. At the end of this stage sauerkraut has an acceptable quality and can be served or canned. If there is enough sugar left, the fermentation will continue until all sugar supply is exhausted.
3. Lactobacillus pentoaceticus ( L.brevis) - continue fermenting until an acidity level of 2.5 - 3% is obtained. As there is no more sugar left in the cabbage the fermentation comes to the end.

• Sauerkraut fermentation.
  

Any change to the above cycles of lactic acid production will alter the taste and quality of sauerkraut. As long as the proper amount of salt is added and the recommended temperatures are observed, the three bacteria strains will ferment cabbage in the proper sequence.

DAY ONE

STARTING

ABSTRACT

I will try to produce Chou croute at home. This delicious food is produced from white cabbage through the process of fermentation. This process is based on transformation of row food to the final product, with the intervention of microorganisms like bacteria, yeast or molds. The microorganisms are transforming the proteins by  which compose the vegetable through the enzymatic procedure. And that happens with the aid   of time or heat changing the flavor of the vegetable. All that processes is known from the ancient times and only the last century the humanity realized the underlying-scientific bases. I will try to give some explanations of the most important issues and their definitions. Like Fermentation, denaturing proteins and the role of microbes enzymes. I  hope to get a delicious result.

 MOTIVATION

I came to the decision to prepare the Chou croute because   I found interesting the fermentation procedure of vegetables  and  the Sauerkraut making. But also for personal reasons.

As Pr. McGee writes ''Fermentation is the process of management by microbes to transform a row plant into foods that resist spoilage.''. It is magic. I think that the making a sauerkraut from fresh cabbage will give me the opportunity to understand how fermentation proceeds in this particular recipe.
I followed the lecture of Pr. Lander from MIT (edx, THE SECRET OF LIFE) and I was fascinated from the miracle of Life in general. Based on proteins and a enzymes. The enzymes are proteins with a special function, though they catalyze -spead up- through lowering the activation energy of a chemical reaction.   I admired the efforts of the scientists to explain Life through the DNA understanding. 

Microbes, yeast and molds are the archaic ancestors of Homo sapient.  They live with us, in us and play a crucial role on our existence and the existence of any living organism, like vegetables.

On the other hand Sauerkraut is delicious, especially for me that I discovered the taste many years ago as student in Vienna. 

THE RECIPIE  '
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ABOUT THE COURSE

Top chefs and Harvard researchers explore how everyday cooking and haute cuisine can illuminate basic principles in physics and engineering, and vice versa.

About this Course

During each week of the course, you will watch as chefs reveal the secrets behind some of their most famous culinary creations — often right in their own restaurants. Inspired by such cooking mastery, the Harvard team will then explain, in simple and sophisticated ways, the science behind the recipe.
Topics will include: soft matter materials, such as emulsions, illustrated by aioli; elasticity, exemplified by the done-ness of a steak; and diffusion, revealed by the phenomenon of spherification, the culinary technique pioneered by Ferran Adrià.
To help you make the link between cooking and science, an “equation of the week” will capture the core scientific concept being explored. You will also have the opportunity to be an experimental scientist in your very own laboratory — your kitchen. By following along with the engaging recipe of the week, taking measurements, and making observations, you will learn to think both like a cook and a scientist. The lab is also one of the most unique components of this course — after all, in what other science course do you get to eat your lab?
Before your course starts, try the new edX Demo where you can explore the fun, interactive learning environment and virtual labs. Learn more.