These days we seem all obsessed with the TDS (Total dissolved Solid) machine in our coffee shops, trying to put up some fancy mathematical equations and numbers but how do they make your coffee taste actually better?
You might probably know the answer already or seen something similar been mentioned, please kindly let me know as I keen to find out more. After all these are just my opinion based on my own experience.
Ok let's take a look at the "extraction equation",
So eventually after you put in all the numbers you will get an extraction in percentage. And let say here an example of an espresso in the shop:
Extraction= 60g * 6.70% / 18g = 22.3%
a VST machine for measuring TDS
<espresso vs milk coffee>
Not bad for an espresso made with a well seasoned and well cleaned grinder ( we used Anfim if you must know which grinder ) and after all the numbers and calculations, I like to give it a taste. With our baristas and myself we all agreed that it tasted all the characteristics that we expected (medium roast), floral, nutty, chocolate like, good body and importantly very high sweetness with very almost none bitterness.
<espresso vs Ristretto>
So the story goes that we pulled another shot with very similar numbers and then made a flat white (essentially another milk based coffee). Surprisingly it tasted a bit flat or blank basically just lacking the essence of coffee. But why? After some thoughts and experiments we found that the milk coffee tastes much better and fuller with a LOWER extraction yield and HIGHER tds% or simply by pulling a bit tighter and shorter shot than the espresso or some may called Ristretto. I know some of you might want to stop reading as soon as you see this word Ristretto but please let me explain.
On the extraction yield equation, if we pull a Ristretto like this:
Extraction = 40g *8.7% / 18g = 19.3%
Which compares to the espresso, the extraction yield is down by 3%! So are you telling me lower extraction yield can taste more "coffee" in your milk drink? Yes. It seems counterintuitive but here is why:
<lower is higher>
Let's take a 180ml coffee cup that we make our latte or whatever milk coffee in. By pulling an espresso you will get about 60ml of coffee and 120ml of milk and that 60ml of espresso is made up of 60g * 6.7% = 4.02g dissolved coffee solid + 56.98g of water. On the other hand for the Ristretto you can actually put in more milk about 140ml into your 180ml cup and again the Ristretto is made up of 40g * 8.7% = 3.48g dissolved coffee solid + 36.52g of water. Forget all the numbers above and I would like to introduce this formula I called "milk - water ratio" which simply represents the intensity of milk in your beverage:
Milk-water ratio = milk/(milk + water) * 100%
If you drink your Americano with a stash of milk basically you are adding a small amount of milk into a large amount of water which dilutes the milk thus the mouth feel and the sweetness is no where near a latte which has a high intensity of milk. So back to the espresso vs Ristretto based milk coffee:
Coffee solid Water Milk Milk intensity
Espresso 4.02g 56.98g 120ml 67.8%
Ristretto 3.48g 36.52g 140ml 79.3%
So here is the figures and you just cannot kill two birds with one stone this time, there's no way the coffee can be extracted without using water. By lowering the extraction yield obviously the coffee intensity is compromised but the beverage will have a higher milk intensity and more fat and sweetness essentially.
<barista vs machine>
Funny thing is the two Espresso and Ristretto examples above are made with the same coffee bean, grinder, grind size, espresso machine, machine settings and dosage. The only difference is the barista use slightly higher tamping pressure on the Ristretto. If you agree with what I just said above regarding making black coffee and milk coffee, all the barista has to do is to tamp accordingly. I see there's some very nice machine that could make very consistence tamping time over time. But does it has the soul to determine how to make your next coffee according to your customer's request? After I think I still prefer the coffee made by hands of my local barista with craftsmanship and passion.