The secret to making espresso is achieving the proper rate of extraction of coffee.
Your goal is to continually monitor the rate of extraction and adjust variables to ensure the coffee is extracting correctly.
As a rough guideline for espresso the rate of extraction should fall between 25-30ml of coffee extracted in 25-30 seconds of brewing. If your shots fall within this time frame the extraction is generally correct (this is not taking into account and compromising factors such as channeling).
This volume/time guideline is just one of the ways we can monitor the rate of extraction. The other extremely important way to check that the extraction is correct is taste.
When looking at the extraction of a shot you should aim for the flow rate of the extraction to flow evenly from the spouts, and we will notice the coffee has a consistency similar to warm honey flowing off a spoon.
Different extraction for each Cirelli Coffee is provided in the following link Cirelli Coffee Extraction for each blend
As the extraction moves towards the end we will notice a significant change in the colour transition of an espresso pour from dark brown and striped to a light, uniform pale blond. This is known as ‘blonding’ and is the visual indicator that we have extracted everything in the basket and that the extraction is finished. This overly blond portion of an espresso is thin, nearly flavourless, and if allowed to continue will dilute the body and taste characteristics of a shot.
- Terminology: Over extracted
- Visual: Dark thin crema
- Flow: slow, dripping and dark
- Amount: Only 10-15mls in 30seconds
- Taste: bitter, astringent, tannic and unbalanced. These flavors will be present at back of the tongue.
TOO QUICKLY :
- Terminology: Under extracted
- Visual: Pale thin crema
- Flow: Gushing and pale
- Amount: 40-60mls in 30seconds
- Taste: acidic and sour and will be dominant along the side of the tongue.
- Terminology: Correct extraction
- Visual: Marbling, creamy
- Flow: Even flow (like warm honey) bonding at the end
- Amount: 25-30mls in 25-30seconds
- Taste: Balanced across the palate, with a balance of acidity, sweetness and bitterness.
Looking at the table below we can see that the look and flavour of an extraction can be caused by 2 main variables: the grind and the dose. It is important for a barista to be able to identify quickly which of these variables is leading to an incorrect extraction so that adjustments can be made quickly without impacting service.
If we were to break up a 30 seconds extraction into 2 x 15sec blocks (as above), the first half will tell us if the grind is correct and the second half will be the dose.
Depending on the blend and machine, we generally want an extraction to start at the 5-7 seconds mark. Therefore, if we see our shots drop earlier than this (3-4 seconds) we have an indication that our grind is too course. Similarly, if we see our shots drop later than this (7-9 seconds), the grind is too fine.
If we have an extraction start at 5-7 seconds, however it begins to blond well before at 28 seconds then most likely the dose is low and we can check this by looking at the puck.
Similarly, if the shot was to start choking up in the second half of the extraction this could indicate that we would need to lower the dose.
Using this visual tool along with checking how the puck feels/looks at the end of the extraction is going to help you determine the correct grind and dose setting.
Obviously tasting your shots is going to be your best tool, however there is no point tasting numerous shots that you know that are going to taste awful, as you will get palate fatigue really quickly and can feel quite sick – so this will also help you to pick the shots you choose to taste more efficiently.