Bob_McBob wrote:You don't need to know how much water was retained in the grounds. You just need to know how much water made it to the top so you can tell how much your measured TDS value was lowered by dilution.

I am wrong again!

This thread just flew on its own!

Eastsideloco wrote:If you brew smaller than rated pots, it stands to reason that the system dynamics will change.

That was exactly what I'm curious about. Certainly there will be some changes in dynamics, I would image 16:1 and 13:1 would extract with a different rate due to the water saturation. But exactly how much and whether it's significant, that's what I intend to find out. It's always easy to buy and use the tried-and-true methods, but not as fun, don't ya agree? And it doesn't hurt that I'm trying to keep my toy as minimal as possible too.

MWJB wrote:With 20% of your brew water remaining in the lower chamber you could see a 20% lower concentration than expected. At full capacity this self corrects.

Stop thinking in terms of the ratio that extraction is taking place at.

The ratio is not important. It was just another way to look at things, and to show how the extraction will take place differently. 20% less water in the top globe will result in a different(higher) TDS and subsequently the extraction yield(probably lower). And to make it more complicated, it's not a direct 20% reduction in TDS after diluted (see below).

MWJB wrote:jpender wrote:
That would only be true if all the dissolved solids were in the beverage. But in an immersion brew a significant amount is left behind in the grounds.

No, it's true in this case (half capacity brew) too.

I would think it matters, or at least consider it before deciding it is insignificant.

A quick calculation : 560g total water, 70g water retention in ground(Usual assumption of twice the ground mass, for vac pot it's lower), 100g water retention at bottom globe. Without ground retention, You have (560-100) 460g coffee diluted with 100g. Dilution is 21.7%. With ground retention, you have (560-100-70) 390g coffee diluted with 100g water. That's 25.6% dilution. The 4% dilution difference will result in a 0.02-0.05% TDS difference. Significant?Probably not so much but it does skew things a little, especially when the retention is significant(and coupled with a few other error/inaccuracy).



p/s: All these are good brain exercises!

It is actually a more complicated calculation than I was thinking because technically you have to know how much brewed coffee the recipe generated so you can separately consider the undiluted retained water and the diluted brewed coffee. In VST-speak (at least as of a couple years ago the last time I checked), at 2.0 g/g retention, those two brews without the unused 100 g water in the lower chamber would make ~400 g, 18.76% and ~901 g, 20.80% beverages if they measured 1.35% TDS before dilution. Adding 100 g water to the brewed coffee would dilute the TDS to 1.08% and 1.22%, respectively. If you ignored the dilution effect and assumed the entire weight of water was involved in brewing and generated beverages at those TDSes, the calculated extractions would be 18.22% and 20.53%, respectively. Those are small but significant differences of 0.54% and 0.27% caused by the retained brewed coffee in the grounds being at a different TDS than the resulting diluted brewed coffee and the brew water weight being incorrect. The immersion brew equation assumes all the brew water ends up at the same TDS.

Again, mostly academic unless the unused water remaining in the bottom makes up a very significant portion of the overall brew water weight and there is a lot of retained water in the grounds. The difference for a full pot for my vac pot is around 0.17%.

Okay, so I did another drying session and got a new data point for the Vac pot this morning.

For that Vac Pot, I was using 16:1 (560g water:35g coffee), ground just a tiny bit finer on the Rosco Mini (finer by 0.05mm than the Espro Press) because I 'wanted' to compensate for the dilution. Also, I noticed that the water in the lower globe today was slightly lesser than what I observed/measured yesterday (probably about 70g-80g instead of 100g). That's because I waited a bit after the water travel up north to get the temperature to brew temp.

My final brew TDS was 1.43%. That means before dilution, it was around 1.7%+-, and extraction yield about 23%+- (depending how much water the ground retained).

Note that this is almost similar recipe for the Espro Press that got me 1.2% TDS, 20% yield (on a different coffee unfortunately, but very similar roast level). I think the sustained temperature and the bubbling action in the Vac Pot may have compensated for the dilution afterwards. I need to coarsen up the grind(for this coffee) but I suspect I will end up somewhere similar to the original Espro Press recipe.

Also, the coffee taste somehow confirms the TDS/yield, in that it has a little after-bitterness, but I wasn't sure it was due to coffee roasting or brewing technique. Without doing this, I would probably put it on the roasting process. In term of strength(TDS), I really have no idea it would score this high because I'm used to espresso. It shows that "go by the taste" is not always the best way.

If this sample point is of any use(many unexpected variables unfortunately), it indicates that the dilution may not be that significant, considering all other factors (higher sustained temp and ground agitation).

Several questions:
1. How much water evaporated during the 1-2 minutes of siphon brewing? Will it change with stirring?
2. Water retained by the cloth filter?

I did a few calculations a while ago with the Clever dripper. There was difference with the lid vs without. I measured the dry lid and lid with condensation to check how much brew evaporated during the three-minute period. The paper filter also absorbed fluid, so I weighed dry filter with coffee and wet filter with spent coffee to adjust for water retention.

In the end, for me at least, the more reliable measurement was just the final TDS.

chang00 wrote:Several questions:
1. How much water evaporated during the 1-2 minutes of siphon brewing? Will it change with stirring?
2. Water retained by the cloth filter?

1. Certainly there will be water that gets evaporated. Honestly I do not know how much.
2. It's a glass rod filter, so the water retention is mostly with the coffee ground.

These are valid extra variables that can be introduced into the equation. They can be measured(probably not now), but will likely differ across different Vac Pot, or even environments(humidity/temp).

The final TDS is important. But if without knowing the process (water loss/retention), I feel it may be meaningless trying to derive the Extraction Yield from the TDS value.

For typical immersion brew extraction calculations, you only need to know the brew water weight, so you can just note how much water is lost to evaporation and subtract it from this value. The TDS increases proportionally, so the calculated extraction remains the same. The water retained in the CCD's paper filter doesn't really affect the calculation since it's mostly the same TDS as the rest of the brew water at the end.

The bottom line here is that you're producing over-extracted coffee and diluting it with water that masks the bitterness. But as you noted, the bitterness doesn't disappear -- it's just muted. A well-balanced cup should taste better.

The dilution doesn't change the extraction yield. What's happening is that only 460g of water is being used for brewing, not 560g. If I plug in a dose of 35g, brew water of 460g and TDS of 1.70% to the VST software (immersion mode), I get an extraction yield of 23.73% -- pretty close to what you estimated. That should taste bitter, even when diluted. The dilution just makes it tolerable.

An interesting experiment would be to increase the dose to 41.5g, keeping the brew water and grind the same. That should give you an extraction yield of 20% and TDS of 1.70% -- before the coffee is diluted.

The extraction yield is right in the middle of the sweet spot and the concentration is very strong -- probably uncomfortably so. But the extra 100g or so of water in the lower globe will dilute the cup considerably, thereby lowering the strength. Hopefully, it will be around 1.35%, which is in the middle of the chart for strength. The result should be a well-balanced cup of moderate strength.

samuellaw178 wrote:This thread just flew on its own!



I would think it matters, or at least consider it before deciding it is insignificant.

A quick calculation : 560g total water, 70g water retention in ground(Usual assumption of twice the ground mass, for vac pot it's lower), 100g water retention at bottom globe. Without ground retention, You have (560-100) 460g coffee diluted with 100g. Dilution is 21.7%. With ground retention, you have (560-100-70) 390g coffee diluted with 100g water. That's 25.6% dilution. The 4% dilution difference will result in a 0.02-0.05% TDS difference. Significant?Probably not so much but it does skew things a little, especially when the retention is significant(and coupled with a few other error/inaccuracy).

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p/s: All these are good brain exercises!

Your charts are significantly flawed. Your siphon is unlikely to retain 2g/g (endless quoting of this figure as if it is a given is not helpful, actually measure it).

You started off by saying you could measure %TDS, so do it.

Here is the rough breakdown, by my way of thinking:

You put 1120g of brew water in the brewer, 70g of grinds.

1020 make it up to the top chamber, let's say it hits 1.25%TDS (~20% immersion yield)
Draw down: about 1.5g/g will likely be left in the bed, so 920g heads south, on the way, it picks up more TDS, I'm going to estimate about 10% for argument's sake. 920g at 1.38% lands in the lower chamber and mixes with the water that remained there (100g) which is close to the same amount that was lost in the bed & diluted back to 1.25%, immersion yield stays the same, drip yield is not significantly affected.

In the half capacity brew: because the water retained in the lower chamber is around twice that retained in the bed in the top chamber, the resulting brew is likely overly diluted, perhaps in the region of 1.09%TDS (in my model). This certainly will reduce concentration and because less water is used in the immersion phase, it will drop the effective yield with respect to the final brew whichever way you look at it (at a comparable %TDS, less water doing the work).

If your brew tastes good but is weak/too diluted, dose up. Brew ratio principally drives target concentration. Use grind & time to nail the extraction yield.

The above is a rough synopsis.

Buying one of the VST Coffee Tools apps will help you enormously.

Hi Mark,

With all due respect, I did. TDS, measured. It's in the post before.

I've also mentioned retention is lesser than 2g/g for siphon. It's in the text you quoted.

The 'picking up TDS' part is interesting. I would love to discuss that, but let's get the context/ambient straight first.

MWJB wrote:If your brew tastes good but is weak/too diluted, dose up. Brew ratio principally drives target concentration. Use grind & time to nail the extraction yield

The variables are not new to me, which I have also implied in my posts. I know extraction yield is driven by grind,steep time,temp,brew ratio,agitation - all which are posted in my previous posts. And again, as I mentioned, I drink espresso mostly, I can't tell for sure my brew is weak or not - because naturally it's weaker than the espresso strength I am used to. That's the reason for the whole measurement exercise, so that I know which direction I have to move the extraction (because my palate is calibrated for espresso).

I know you may have not meant the tone you'd come across. To me, it sounded quite offensive because you had made yourself sounded like the absolute authority with a derogative tone and as if I know nothing (but all the information I had already posted if you do read).

My suggestion for a more productive discussion(not ended with the thread locked), it will help if you read your message before you post it, also it will also help immensely that you have read CAREFULLY what was posted before. Because, simply, I believe most of the people here are putting their great effort and forming their thoughts carefully before they let it out, so that HB stays as a place for high quality discussion. I know I do. That's also the reason I love and have stayed here at HB for so long even if I don't post (unless I've got something significant/important to share).

And your tips/guides posted are noted. Thanks, I do appreciate them.