Reaction Analysis of Coffee roasting process what is the effect of Mena reaction and caramelization reaction in roasting

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Professional coffee roasting| Coffee roasting too complicated? A picture teaches you to understand the baking process

After working in coffee roasting, I found that many principles are actually interlinked. I found that raw beans are like actors, and roasters are like directors, who can direct the life and death of actors in this play.

It can be said that apart from green bean quality, roasting is the variable that affects the taste of the whole cup of coffee the most.

To me, baking is the combination of water, fire and wind.

water

Many people may wonder, how can there be water, do you add water when roasting coffee beans? In fact, it is the moisture contained in the coffee beans. Normally, the moisture in the coffee beans accounts for about 8-13% of the whole coffee beans. Therefore, we often hear roasters discussing how long the dehydration time is, or how the moisture of the coffee beans is... In the whole roasting process, we will find that the coffee beans turn yellow at 150℃-160℃, and the bean surface expands rapidly. Many people call this stage the 'dehydration stage', but in fact, the coffee beans start from the next bean to the first explosion. This stage is the true 'dehydration stage' and the temperature is between 150℃ and 160 ℃, the moisture will be greatly removed, so it will affect the whole baking period is not undercooked, so I will call it the 'breaking point'.

As we all know, moisture loss from the surface of coffee beans, coffee beans surface temperature due to baking and rise, moisture evaporation, and the beans are gradually moving to the center of the moisture, this principle you can do a test yourself, such as take a cup of water, put a piece of tissue 1/3 in the cup, the remaining 2/3 on the outside, we can see after a while the whole piece of paper is completely wet. This is the same reason, and after the moisture in the bean core moves to the bean surface, it will evaporate when it meets the heat in the bean surface, so baking takes a certain amount of time, rather than turning the fire to the maximum and blackening the coffee beans.

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Because the evaporation of moisture in the bean surface and bean core is completely different during roasting, sometimes when roasting too fast, it is easy to cause uneven moisture in the whole coffee bean, resulting in vitrification of the skin, leaving only the bean core uncooked, resulting in astringent and grassy coffee.

Therefore, in the early stage of baking, we will pay more attention to the method of 'steaming and baking' for dehydration, that is, about 5-7 minutes in the early stage.(The following data are 1-2 kg of roasting amount), so that the moisture of coffee beans is more evenly distributed in each corner, under normal circumstances, the use of small damper small fire dehydration, unified beans in the boiler state, if the steaming roasting does not handle the dehydration state of coffee beans, there will be uneven roasting, and produce astringent taste.

Of course, the so-called 'dehydration' is not to remove all the moisture from the coffee beans, because in the process of roasting, the moisture is more as a heat transfer medium, so if we remove the moisture too early, then the coffee beans lack moisture to conduct heat to the bean core, and it is easy to appear.

fire

The fire mentioned here mainly refers to heat sources. The source of heat is direct fire, electric heat, infrared rays, etc. In theory, the heat source does not change too much taste, but the uniformity of the heat source will affect the taste of coffee. For example, direct fire and electric heat, the advantage of direct fire is that the heating rate is faster, the penetration of the flame is high, but the uniformity of boiler heating may not be as good as electric heat, which will inevitably affect the impact of these two common heat sources on taste.

When most of the coffee beans are dehydrated, that is, at about 150-160 ° C, the whole bean type will expand rapidly, and the color of the bean surface will turn yellow. At this time, the coffee beans will be taken out with a sampling stick. The coffee beans have begun to have some sweet aroma, which indicates that the coffee has begun to undergo Mena reaction. A lot of bakers increase their heat here. In fact, what we need to deal with here is 'chlorogenic acid'. In fact, it is the change caused by the treatment of chlorogenic acid through firepower, which is also closely related to the treatment of water in front of us.

I get used to dividing the bitterness in coffee into good bitterness and bad bitterness. The good bitterness brings about the bitterness of chocolate, cocoa, roasted nuts, etc., while the bad bitterness gives people the feeling of burning wood, smoke, etc. When we drink a cup of bitterness to make you feel sweet, and with a chocolate-like feeling, indicating that coffee produces 'green acid lactone' when roasting, that is, caffeic acid and quinic acid produce dehydration condensation substances, this is due to chlorogenic acid quinic acid in dehydration when a water molecule is lost, so combined with caffeic acid, resulting in chlorogenic acid lactone, generally speaking, such bitterness is only produced in the case of high completion of the previous dehydration. The bad bitterness comes from the vinyl catechol polymer produced by caffeic acid, which is generally found in coffee beans that fail to remove moisture. In the case of failure to remove moisture, the water molecule content is more, so there will be a reaction of hydrolysis, that is, chlorogenic acid is decomposed into caffeic acid and quinic acid. The caffeic acid itself will make the coffee astringent. In addition, ethylene catechol polymer will be produced during high temperature heating, which will make the whole cup of coffee bitter and astringent.

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At the end of dehydration, roasters are faced with such a choice. At this time, there will be a little water left in the raw beans, which makes chlorogenic acid face the hydrolysis reaction. Therefore, many roasters will use a large amount of heat to make the coffee beans pass through the hydrolysis zone quickly at 150-160℃, thus achieving the effect of dehydration condensation.

The firepower is generally not adjusted too many times during the whole roasting process, but each adjustment is predicted by the roaster when the coffee bean reacts internally, so that the whole cup of coffee has a better texture and flavor level.

wind

The wind mentioned here refers to the actual exhaust gas situation in the boiler of the baking machine, that is, the wind pressure condition of the air control valve.

The baker's operation of the baking machine is nothing more than the adjustment of the firepower and exhaust volume. Generally speaking, we don't make too many adjustments to the firepower, but the exhaust volume will have more adjustments. In semi-straight lighters, the damper adjustment is not only used to exhaust smoke, but also to control the heat source by changing the damper.

Different roasters will have different roasting methods, some are used to reduce the fire before the coffee beans enter the first explosion, and some are used to increase the fire after the coffee beans enter the first explosion, but no matter how the fire is adjusted, the damper will be adjusted accordingly. It should be said that the adjustment of the control valve is no less important than the adjustment of the firepower, but the purpose of adjustment is more to ensure the balance of positive and negative pressure in the boiler, followed by the control of the intake condition of the heat source, and finally to achieve effective exhaust or discharge of excess water molecules.

Because dehydration will determine the fate of coffee beans in the boiler, the moisture removed will often be discharged from the exhaust pipe by the control valve. Therefore, when we roast coffee beans to about 160℃, we will feel the gas discharged at this time with our hands. It will feel that the gas is a little wet, which indicates that the moisture is being discharged. I once made a high temperature hygrometer and put it in the exhaust pipe for testing. Unfortunately, due to the relationship between roasting machines, such tests failed to produce reference value.

With my personal baking habits, I prefer to use a larger air volume to pursue the stability of the hot air and to be able to quickly dehydrate. Of course, the use of larger air volume to match the actual firepower situation, which requires everyone to adjust the control valve according to their own machines and baking habits.

The next step is to talk about two of the most important reactions in coffee roasting, caramelization and mena. A long time ago, it was still the public account of Maoshu Coffee (now the public account of Maoshu Coffee is renamed CHAICAFE). I briefly introduced what the Mena reaction is. I introduced it about…three years ago. At that time, there was actually no detailed understanding of the Mena reaction. I thought that only coffee would produce the Mena reaction. It turned out that the Menard reaction occurred in all aspects of diet, so to study the Menard reaction, I had to eat how much meat over the past three years to get this fat. Back then, I was still thin and handsome…

caramelization reaction

The sugar content in coffee beans undergoes caramelization reaction at about 170--200℃, which is exactly the melting point of sucrose (185℃) and the temperature of the first explosion stage of coffee beans roasting. The products of caramelization are divided into two parts:

1. The dehydrated product of sugar is caramel or brown

2, cracking products, mainly some volatile aldehydes and ketones.

In general, caramelization produces roasted aromas, caramels, and colors, as well as other aromatic compounds such as maltol, Cyclotene, furans, and so on, which can also be found in red wine, juice, cream, and other foods.

However, if you caramelize too much during the roasting process, it is not a good thing. Instead, it will cause carbonization and make the coffee dry and bitter. If not caramelized enough, the aroma will be dull and lack of depth.

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Maillard reaction

Roasted coffee beans unique aroma, which has a plant fiber burning blue-blue smoke burnt flavor, creamy yellow sweet aroma, brown toast bread aroma and so on a variety of flavors gathered together. Most of these rich flavors come from the Menard reaction during baking.

Menard reaction can be divided into three stages

1. Initial stage:

Amadori Molecular Rearrangement by Carbonylamine Condensation

II. Medium-term:

Amadori molecular rearrangement product fructosamine dehydration to HMF (hydroxymethylfurural)

Deamination of fructosamine to reduce ketone

Interaction between Amino Acids and Dicarbonyl Compounds

III. Final Stage:

aldol condensation

Melanin-forming polymerization

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(The above is Hodge's proposed reaction process, which is also the most widely used version at present)

The above information is found on the Internet, so let's say the conclusion first! Both are browning reactions, the difference is:

Caramelization: The process of molecular disintegration of sugar when heated.

Menard reaction: the color and aroma of fried onions, toast, and fried steak that occurs when "sugar or starch" is cooked with ingredients that contain "protein or amino acids."

Caramelization vs. How does the mena reaction happen?

It is often said that charred onions are "caramelized," but caramelization occurs only in foods that contain sugar alone. Sugar is heated to about 365 degrees Fahrenheit (185 degrees Celsius) and dissolves into a clear liquid. If it is heated, it will turn yellow, light brown, dark brown, and finally black carbon, which is the process of dehydration of sugar. And sugar usually smells tasteless until it is heated, and the molecules begin to break down to emit wonderful, complex volatile molecules that produce sour, bitter flavors, and the darker the color, the more bitter the taste.

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When sugar is cooked with proteins or amino acids, a Maillard reaction occurs. In addition to caramelization, some sugars interact with the latter in a series of chemical reactions, resulting in a more diverse range of compounds, in short, flavor is richer than caramelization, not only coffee beans, chocolate, maple syrup, brewing beer and so on are the final products of Mena reaction.

Caramelization and Mena reactions each produce the following aromas:

- Caramelization: sweet, sour, bitter, fruity, sherry, creamy, caramel, nutty

- Menard reaction: salty, floral, onion and meaty, green vegetable, chocolate, potato and earthy, caramelized aromas mentioned above

In other words, both will happen simultaneously. However, the complex chemistry of caramelization and Menard reactions has not yet been fully understood by scientists, and many of the compounds with full flavor are not fully recognized.

How was the Mena reaction detected?

French chemist louis-camillemaillard discovered the menard reaction in 1912. Originally he wanted to study how amino acids bind to proteins, but he found that when he heated sugar and amino acids together, the mixture gradually turned brown. But in fact, until the 1940s, scientists didn't know that Mena reactions produced flavors. During World War II, many soldiers complained that egg powder, a substitute for eggs, turned brown and gave off an unpleasant smell when cooked. After numerous studies, scientists found that the off-tasting taste came from browning reactions. Although the egg powder was dehydrated and stored at room temperature, the concentration of amino acids and sugars was still sufficient to cause changes.

Most of the research was done around the 1940s and 1950s, when scientists confirmed that Menard reactions produce particular "tastes" and "odors," the most complete of which was done by John E.Hodge, who provided some fragmentary information.

Conditions for producing Menard reaction

You already know that Mena reaction is caused by changes in sugar, amino acids and proteins after heating, and it is also a source of tempting delicacy. The basic conditions for successfully creating Mena reaction are:

- Protein

- Reducing sugar: glucose, fructose, maltose, lactose, etc.

- High temperature.

- Keep dry without moisture

- Alkaline material speeds up reaction (not necessary)

For example, caramel sauce and milk caramel sauce (dulce de leche) just can clearly distinguish the difference between caramelization and Mena reaction, the former will boil sugar to charring after quenching, finally pour cream or cream and other dairy products; the latter is to slowly cook condensed milk for several hours, because the beginning of heating already contains protein, and cooking temperature is lower than caramel, taste each flavor.

Since sucrose is not a reducing sugar, it does not directly cause the Menard reaction, but it will break down into glucose and fructose during cooking, so there is no need to worry about adding reducing sugar.

What is the temperature at which Mena browning occurs? It's about 118 degrees Celsius. In other words, when the coffee beans begin to roast, the Mena reaction begins, that is, the Mena reaction produces such a rich flavor in the coffee roasting process, it should be said that the whole coffee roasting revolves around how to make the Mena reaction produce a better flavor.

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