Cold Brew Online Seminar Day 2

On day two, we started the session by letting Dr Steffen Schwarz and Dr Dirk Lachenmeier answer some questions posted by our participants in the event poll.

Q:  What makes 70% extraction rate optimal for cold brew?

A:  We know from all other coffee extraction practices that 100% extraction rate is not the goal for well extracted coffee, so we can predict with confidence that it’s the same for cold brew. The 70% is not a scientific number, but a hypothetical number for a balance cold brew extraction. It’s a reminder that there might be a point of extraction (below 100%) that can bring out most of the good flavours into the cup and leave out the unpleasant ones. Please bear in mind that 70% extraction rate is a derivative from the total extractable amount out of coffee (which is approximately 30% from the entire coffee bean). Flavours in the cup is still the best guide to finding your optimum extraction rate for cold brew

 Q: What are typical customer's complaints against cold brew (too bitter, too acidic etc)? In other words, what needs to be improved?

A: This depends on where you are from. In Germany, they usually don’t complain they just won’t come back. Customers will most likely complain about flavours that are generally perceived as negative according to their culture and background. For example, bitterness is a common one as it could indicate toxicity, but in some cultures, they embrace bitterness as something good for health. Sourness is another one. Especially in the case of cold brew, due to the long brew time and contamination risk factors, one might associate sourness with rottenness. 

Q: What would be the optimum shelf life of cold brew coffee?

A: The highest risk of cold brew coffee is microorganism contamination. As long as it’s not contaminated, you can use it for quite a while as there aren’t many other factors at play.  But it could still turn stale, just not as fast because there isn’t as much oil compared to hot brews. The safest practice is to reduce chances of contamination by reducing the exposure of the product to an uncontrolled environment to as short as possible, maximum two days.

Q: What are the risks of handling cold brew incorrectly?

A: Like many other food products, handling cold brew incorrectly could result in health issues and a disaster for business. The biggest risk is not being able to see the contamination as it happens. You may only taste that it’s off later on in the contamination. Cold brew coffee is an alcohol-free, sugar-containing beverage and there are international safety guidelines on how to clean dispensing equipment based on the amount of alcohol and sugar content of the beverage. Risk of contamination for cold brew based on this is approximately between beer (higher alcohol and sugar content) and coke (much higher sugar content)

Q: What is the fastest time to create a cold brew?

A: We haven’t got any scientific findings regarding this, but as far as our practice goes, two hours seems to be the fastest brew time that can create a palatable cold brew. But keep in mind, all the other factors such as grind size, ratio, water quality and roast could play a major role in yielding such results. The key is to do your own controlled experiments and make records to find slight adjustments that can improve your cold brew coffee.

Q: Why do I taste alcohol in my cold brew the longer I store it?

A: It’s most likely that there is a yeast being cultivated, which is fairly common in cold brew coffee.

Q: How does sugar content affect the shelf life of cold brew coffee?

A: It depends on the level of sugar content, as it could have two opposite effects. For example if your sugar content is as high as jam and syrup it will greatly prolong shelf life. But the amount of sugar in cold brew is usually on the lower spectrum thus it may promote contamination as a source of food for bacteria. 

Here are some points from the second part of Dr Schwarz’s presentation

To further elaborate on the effects of water-bond and oil-bond aromas reacting to different brewing methods, we have compared the flavour profile of the same coffee (an Oeiras variety) in both cold brew and hot filter methods.

• In the cold brew sample, it expresses more orange and lemon cluster of flavours, it also gives a higher vegetal note (in this case, cucumber note)

• In the hot filter sample, it presents more peach flavours than citrus, less intense in overall fruit and roast aromas, but more prominent in the lumber, spices, nut, and lactic categories in which are more oil-bound aromas.

We will now share and compare some of our roast profiles done with a sample roaster at Coffee Consulate between cold brew, filter, and espresso. Please note that roasting time was relatively shorter in all three profiles due to the size of the roaster.

• Pay most attention to the line in dark blue as that line represents temperature variations through the entire roast time.

• As we can see there is a smaller difference between cold brew and filter while the bigger difference lies in espresso roasting.

• However, these are not the international guidelines for the three roasting styles, your variables in roasting should still take into account all the other factors that may influence the final product such as your water quality and grinder and so on.

• Now for the interesting part, if you compare all three profiles in the last chart, phase one is pretty much identical, so we don’t have to pay too much attention there, a shorter phase two (drying phase) is the key difference here for cold brew roast profile (grey line). And the main reason for that is to preserve more acids inside the coffee, though we also want to promote acidity in filter coffee, it’s not as much as cold brew. And there is also a slight difference in phase three where we want to bring out more aromas in the cold brew profile by trading in more sugars in the Millard reaction.

That’s all our notes on the cold brew online seminar, for the Chinese version, please click here.

If you have questions or anything to add to our notes, feel free to leave a comment below, we are keen to learn and improve together with you as we get past these difficult times.

More online seminars like this will be coming in the future, follow our Facebook page to stay updated!