I'm experimenting at making a coffee concentrate. I've been making a strong cold brew and then boiling it down to concentrate it.
I boil it at room temperature using a vacuum so as not to further cook or burn the coffee.

My question is whether there is any difference between concentrating coffee in this way vs. just using a higher ratio of ground coffee to water?
Is there any difference between 100g coffee + 500ml water => reduced by 50% with boiling vs 200g coffee + 500ml water and no boiling?
What is the limit of how concentrated one can make coffee by just increasing the ratio of grounds to water?

Reduction through evaporation is a type of distillation. The more volatile compounds will vaporize preferentially, at any temperature. So in addition to all the water you remove you will also remove aromatic compounds. How much this affects the taste will depend on the type of coffee and how far you take it. My understanding is that producers of instant coffee often attempt to capture these volatiles and reintroduce them later in the process.

The limiting factor on brewing a concentrate, immersion style, is the fact that the grounds hold roughly an equal weight of liquid coffee. It gets increasingly expensive as you push the concentration higher. It's more efficient to pull ristrettos on an espresso machine, but it's also more effort.

javaman wrote:I'm experimenting at making a coffee concentrate. I've been making a strong cold brew and then boiling it down to concentrate it.
I boil it at room temperature using a vacuum so as not to further cook or burn the coffee.

My question is whether there is any difference between concentrating coffee in this way vs. just using a higher ratio of ground coffee to water?
Is there any difference between 100g coffee + 500ml water => reduced by 50% with boiling vs 200g coffee + 500ml water and no boiling?
What is the limit of how concentrated one can make coffee by just increasing the ratio of grounds to water?

Coffee absorbs it's weight in water so a 100g of coffee with 500ml of water would have a brewed weight of about 400g. if the dose was 200g then the brewed weight would be 300g which would throw the numbers (at least on paper). let's fake some of the numbers and say you have a TDS of 5%

Extraction yeild (E) x Dose (D) = TDS (T) x Beverage Mass (B) or "ED = TB"

Cup A (1:5 ratio)
E=5x400/100
E=20 (a respectable extraction)

Cup B (reduced)
E=10x400/100
E=20

so if you reduce the liquid by half and keep the coffee stuff the TDS would double and the extraction would stay the same (at least on paper). but if you if double the dose you double the TDS but also double the absorption of water in the coffee

Cup C (1/2.5 ratio)
E=10x300/200
E=15

Cup C would have a lower extration in this case than Cup B because of the factor of the beverage mass loss. but this is all on paper and how the actual numbers are is probably going to vary and that whole abortion thing is pretty fuzzy. since it's all cold brew I'm not sure if aromatic compounds matter much since cold brew already sacrifices that due to the long brew times. If you wanted to double the dose you should compensate for the aborbtion and add another 100ml of water for a total of 600ml. the absorption brings it down to 400 which puts it on par with the others and the extraction should be the same.

refractometers and blind taste tests would be more conclusive and can confirm how predictable the TDS is with such crazy ratios plus simply weighing the cold brew after you remove the coffee grounds can confirm how much the volume actually changes. with so much coffee to water the TDS in the interstellar fluid (extraction trapped in the coffee bed) probably throws everything too much.

In all seriousness, high-volume, high-TDS extraction shown and discussed at The craziest %#*$ing thing I've seen all day...

As I recall, they claim 8% TDS. A classic, 1:2 shot with good coffee and gear is usually somewhere in the 10-12% TDS ballpark.

Brewed coffee is often in the 1-2% TDS range, so you're probably looking at around 5-10x concentration to be comparable to espresso.

Thanks for these interesting observations. If I understand them correctly... if my goal is to make a small volume of the highest concentration coffee then I would be better off making 10+ shots of espresso and possibly distilling that with low temp evaporation. (At the cost of losing the volatile/aromatic compounds.).

The highest concentration would be 100%. What concentration are you aiming for?

javaman wrote:Thanks for these interesting observations. If I understand them correctly... if my goal is to make a small volume of the highest concentration coffee then I would be better off making 10+ shots of espresso and possibly distilling that with low temp evaporation. (At the cost of losing the volatile/aromatic compounds.).

With espresso if the TDS was 10%, dose 20 and yeild 40 this is an extraction yield of 20%

E=10*40/20
E=20

Doing 10 of these is just the same thing. Same TDS and same extraction it's just the dose/yeild is multiplied by a factor of 10

E=10*400/200
E=20

It doesn't matter how much you add or reduce the extraction yeild stays the same since it's about how much coffee stuff you already extracted so when the brew is finished you can't increase/decrease it and it's just remains at a static number. So if you reduce it by half through evaporation in a vacuum (which I think is really interesting) you double the TDS so that the extraction stays the same

E=20*200/200
E=20

I don't know how concentrated you can get a mixture in practical terms but if you did reduce it so there is no more liquid then what remains is the pure extraction in some sort of powder form and basically is instant coffee. In order to get that you need to increase the TDS to 100 which is multipling it by 10 which means dividing the yeild by 10 reducing it to 40.

E=100*40/200
E=20

Or in another way 40/200*100 is your raw extraction meaning of the original dose of 200g, 40g of coffee stuff made it to your cup. Or as a single shot of 20g, 4g was extracted. This of course assumes the original single shot was at a TDS of 10% (or average of all the 10 shots) but your TDS may be lower/higher.

javaman wrote:Thanks for these interesting observations. If I understand them correctly... if my goal is to make a small volume of the highest concentration coffee then I would be better off making 10+ shots of espresso and possibly distilling that with low temp evaporation. (At the cost of losing the volatile/aromatic compounds.).

I don't know what you're trying to do. But if it's quality coffee you are hoping to be drinking then I suspect any sort of evaporation process is going to lower the quality significantly.

Check out what Cometeer is doing. They are secretive about their process but what the sell are small (~25g) capsules of frozen coffee concentrate which are at 14% TDS, according to the CEO. That's a concentration that can be achieved with an espresso machine, no additional dehydration necessary. Cometeer freezes their concentrate in liquid nitrogen which likely improves storage life. Liquid espresso in the refrigerator will be a lot less durable.

braxtonjens wrote:If your looking to concentrate your coffee,
Do a freeze distillation.
That will cut out water content and effectively concentrate your coffee.
This will keep those nice aromatics from being boiled off.

What is the limit of freeze concentration with coffee?