July 2013 - the vital role of acid in coffee

Date Posted:1 July 2013 

This month we discuss the influencing role acid plays in roasting and extracting (brewing) coffee.


Roasted coffee has natural acids present and the levels are determined by the bean type (varietal), farming environmental conditions such as soil, etc. the processing method (washed, sundried or naturally pulped) and the roasting profile (depth) applied to the raw beans.

Generally speaking, darker roasts remove more acids from the coffee beans.

Certain origins such as Central American growing regions like Guatemala, Costa Rica, Honduras, Nicaragua, El Salvador, Panama, etc. tend to produce coffee beans with higher acidity levels - making them ideal for matching with milk-based espresso brews.

Countries like Sumatra (Indonesia) can have low acid coffees whilst some of the South American origins like Brazil can produce coffees with neutral acidity.

Typically, the roaster has the primary control over acid - deciding how to best showcase the particular bean (or beans in the case of blends).

Experienced coffee roasters look closely at acid - it becomes a core part of their analysis when it is for reviewing or assesing new beans or inspecting the quality of recently roasted batches.

The most skilful of coffee roasters know how to harness the acid in a bean - or tame it.

Acid can be a desirable attribute in a coffee - when extracted (or brewed) correctly, acid can provide a clean, sweet and uplifting finish to a coffee, especially when milk is added to the beverage like espresso - the acid in the extracted coffee blends or fuses with the alkaline in the milk.

Controlling acid in a bean (or blend) can be challenging for a coffee roaster as the acid levels can change as the coffee beans age.

Excessive acid in coffee beans can be mistaken as bitterness or in some cases sourness.

This can be even more detectable if the extraction was not ideal where acids and bitter taints affect the overall cup quality.

In Australia, there is an overwhelming trend to roast with positive acid levels due to the 95% (roughly) ratio of milk-based coffees compared to black-only coffees.

In other countries like Europe and US, the ratio of milk-versus-black is different and thus coffee bean roasters will generally roast darker to remove acids from the coffee beans (or blends).

Sometimes, the darker roasting levels are not necessarily because of acids but due to those coffee bean roasters employing lower grade raw coffee beans and thus roasting out some of those defects.

Each person has different sensitivities to what is the "best" acid balances - it's an individual thing.

For those coffee drinkers who enjoy a lot of milk with their espresso beverage, e.g. big mugs of flat white, latte, cappuccino, etc. they are probably best to seek coffees from Central America with sparkling (or sharp) acidity to cut through milk.

Coffee drinkers who enjoy it black should look for Brazil, Sumatra, Colombia, PNG and some Ethiopian beans as they have more balanced acidity.

Lighter roasts tend to retain higher levels of acids within the coffee bean.

The acids can be masked as "fruit" and for certain types of brewing methods like Filter, Syphon or press, these lighter roasts and fruity acids provide a wonderful extraction when prepared black - sweet, liquor-like flavors.

Lighter roasts can also suit ristretto-style espresso extraction.

A common trend over the last few years in high-end cafes is to deploy light roasts with a double-ristretto (or double-rizzy) shots on the espresso machine - producing short, intense, fruity extractions.

These types of extraction may at times not work with milk and in the more extreme cases you can see the higher acids react with soy milk.

A light roasted coffee bean used with a lot of milk may lack the chocolate, caramel and flavor many coffee drinkers desire.

Dark roasted coffee beans can taste charry-ashy when extracted using the hipster double-rizzy style.

This may suit milk drinkers as the sweetness of the milk may balance the sourness or sharpness of the espresso shot.

Medium roasted coffee beans are difficult - it's a double-edge sword.

Trying to roast all types of coffees in a medium style can result in some very weird acid balances - not everything will work, or it may not suit everyone's taste.

There is a theory that coffee beans should be roasted to suit the precise nature or character of that bean.

This sounds ideal, however, in practice we have found that coffee needs to be roasted to suit the direct of the market, e.g. roasting coffee beans to suit or match what customers are demanding - this is no easy feat.

We recognize that the majority of our customer base have access to some type of espresso extraction method - whether this is a machine (domestic or commercial) or stovetop/moka pot.

We also acknowledge that around 95% of the coffee drinkers put milk in their brew.

If you are confused, or unsure about what coffee to select - please either contact us via our webpage, call us, or purchase the Roaster's Choice product and provide a description of what you need and we will do our best to match it for you.

Finally, we would like to thank all our wonderful customers for the tremendous support and loyalty over the last 12 months and we wish you many memorable brews in FY14.

The mycuppa team - Jeff, Dianne, Tony, Pete, Chanh, Thomas and Matty.