The Basics of Coffee Extraction

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Whatever method of coffee extraction we use, coffee needs a solvent.

Water, in fact, is one of the best solvents that we have in nature especially for its chemical properties: it’s super attractive with hydrophilic substances, substances that have molecules that can absorb water.

The better way to extract the molecules inside of a coffee’s beans is to make as more contact surface as possible to let the water get closer and extract as many flavors as we need. Once we have our ground coffee we can go on to the extraction. Now we have to ask ourselves: which is the proper dose of coffee that we are going to use?

If we are going to used arabica beans instead of robusta beans we will need more grams of coffee. Arabica beans grow at high altitudes and are, therefore, thicker and less soluble than robusta beans; it is usually preferred to be extracted at higher temperature instead of robusta beans. We can set a range between 88-94 grades centigrade which is the standard range of the water temperature in the majority of the extraction systems.

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Image courtesy of http://reddiamondbevservice.com

After setting the proper ratio between grams and water temperature, we can proceed with the time. If our recipe will be flat and/or sour we will in the case of under-extraction, if it will be astringent and/or bitter we will in the case of over-extraction.

We can use a tool called refractometer whenever we want to know if we are extracting the proper amount of solids in the cup. For brewing recipes, the recommended range is between 1,20% and 1,45% whereas espresso recipes are between 8% and 12%. However, as regards the extraction, we are in the range between 18-22 % for brewing recipes and 18-21% for espresso recipes. Below 18% we are going to under extract and above 22% we are going to over-extract (23% in the case of brewing recipes).

The refractometer is a great assessment tool but we don’t have to dwell only on these criteria. The most important evaluation relates to our palate. There will be cases in which the solids will not be within the established range (determined by the Coffee Brewing Institute around 1950), but it will not mean that we will extract improperly.

ABOUT THE YIELD

The Yield is basically the weight of the liquid that we obtain in the cup.

The Yield is the starting point for every barista that wants to improve itself and serve the best for its customers. When we talk about the yield, we don’t focus only on the extraction time: the time is a consequence of what recipe we want to obtain.

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In simple terms, more or less yield means more or less liquid in the cup. More yield means as well more body, fewer flavors and more bitter; less yield means more body and more flavors, but as well more sourness. The quicker we learn about this concept the more we can try to find a proper balance in the cup.

A standard yield is usually twice the amount of the dose we grind. So, for example, if we grind 20 grams of coffee, the yield will be of 40 grams. When we will be satisfied with the yield, we can memorize it on the machine so that we can replicate it. A short explanation: the caffeine will never increase if we increase the yield: more than 70% of the caffeine is extracted in the firsts few seconds.

Too often we overlook or we take for granted that we are the ones that prejudice the final result. If we don’t pay attention to every single action the result can only be affected.

We have to make sure that we are grinding with the proper granulometry, putting the proper dose of coffee in the filter holder, tamping correctly with the tamper and close the filter holder without hitting it on the group, avoiding any channelling effect that would lead to an under extraction in the cup.

So now that we have learnt about the yield, we can have fun extracting a balance shot of coffee for every origin we are going to use. We can define an espresso as “balanced” when sweetness, sourness, and body are perfectly mixed together.

The acids and the fats are the first components that are being soluted in the cup while the sugars are next to be extracted, followed by the bitterness components. The body then will be given to the brew ratio that we will use.

BREW RATIO

The brew ratio is the ratio between the amount of ground coffee and the quantity of water that we will use. The water will, therefore, affect the flavors: less water means we will not extract all the flavors we wanted, while more water means that we will extract undesirable flavors like bitter ones. If for espresso the standard ratio is 1:2, brewing method is about 1: 1,16 which means one gram of coffee ever 16 grams of water.

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