Why Isn't My Cold Brew Sweet?

Voca Coffee Notes #11 - Causes of Under-Extraction in Cold Brew

Deep into the Summer: Time for some ice-chilled coffee!

This morning, when a Voca friend came to pick up coffee beans, he shared with me that he had been experimenting with cold brew lately and the coffee came out with good acidity but not sweet enough. So why was it not sweet enough? Giving good coffee beans were used, the culprit was clearly under-extraction.

Cold brew is a type of immersion coffee brew by soaking coffee grinds in cold or even chilled water, with bean-to water-ratio of 1:10 to 1:15, give it a few gentle stirs and leaving it in refrigerator for 12~24 hours, and then filtering out the coffee grinds and ready to serve. Cold brew can result in nice crisp clean and flavorful coffee, with sweetness for sure.

In cold brew, the common causes of under-extraction can be:

1. Coffee grinds are too coarse
2. Soaking time is not long enough
3. Problem with built-in filters

Grind Size: Coarse or Medium Fine

Most cold brew videos and blogs would recommend you to use coarse grind size for cold brew. This is a good starting point, however, coffee bean roasts are different. You got to adjust the grinder setting to suit your coffee beans. If coarse grind size results in acidity but inadequate sweetness, adjust the grind size finer.

In fact, you can even go as fine as medium fine. Here is a reference to medium fine grind size:

The grind granular size is similar to raw cane sugar.

Would it cause over-extraction if grind it this fine? Actually, there is no need to worry - cold brew, as an immersion brew, extracts coffee flavors gently - unless being agitated outrageously, it is difficult to over-extract.

The finer the coffee grinds are, the easier the flavors can be extracted. Therefore, for more extraction, go for Medium Fine.

Soaking Time: 12~24 Hours

Depends on your grind size, the soaking time can be adjusted. In general longer soaking time resulted in more extracted coffee; the finer the grinds, the shorter the soaking time can be. If you don't want to wait for too long, you may choose Medium Fine grind size. As a rule of thumb:12 hours would be minimum, and 24 hours are usually more than enough.

Handling Built-in Filters

Some cold brew pots, like Hario, may come with built-in filters in the middle. These filters may look convenient but have a few pit-holes:

1. some fine grinds may leak through the mesh
2. the coffee oil build-up and some fine coffee grinds may clog the mesh

I am not a big fan of reusable filters - in fact, I prefer one-time-use paper filters, which result in much cleaner coffee. To make cold brew, I would simply put coffee grinds in a clean jar, add water and give it 10 stirs; after 12~24 hours of fridge, I would filer it through my regular pour over coffee filter - that's it - clean and simple.

If you do prefer using built-in filters, you may keep the coffee grind size to be coarse enough, and wait longer. To unclog the filters, you may clean it often by soaking it in cleaning solution with specialized coffee equipment cleaning powder.

Do you like cold brew? How do you brew it? Have you encountered similar issues? Or you prefer flash-chilled? What types of coffee brew do you enjoy in Summer? I'd like to hear.

Happy Summer and enjoy the coffee!