This link should be informative:

Espresso Brewing Control Chart

-Greg

gscace wrote:This link should be informative:

Espresso Brewing Control Chart

Simply measuring shifts in brew-ratios ("solids yield") will tell us very little about the effects on flavor of various pressure profiles. As the article from U.C. Davis states, some compounds have no impact on flavor. Others that do have profound effect on flavor evade measurement because they're active at a few parts per trillion.

The central point of that UC Davis article on wine (which also discusses capturing of volatiles with gas chromatography) is that the "hard data" alone won't tell us much; they must be correlated with the taste findings of a panel of tasters.

A reduction in pressure that results in a lower solids yield could well preserve aromatic compounds that disappear when the pressure is increased, and/or an increase in pressure might increase the amount of solids that result in flavors that are not liked.

Nick at Murkycoffee wrote:... measuring a quantity of solubles is a far cry from measuring the quality of those solubles. ... It doesn't tell you whether those solubles were the (predominantly) kind that you want, vs. the kind you don't want. ...

dsc wrote:
So I thought it might be a good idea to get a thermoblock, stick a boiler in front of it and control the heaters within the thermoblock to get the water to the right temperature. This is something my friend did, with a small thermoblock machine which he PIDed and added a small 700ml boiler to pre-heat the water entering the thermoblock.

Regards,
dsc.

Is it just me, or does this fall straight into the category of "Why the hell would you even bother?!!" The defining characteristic and major weakness of any thermoblock is that the difference between entry water temperature and exit water temperature is dependent on the flow rate within the thermoblock. Given sufficient block heating and channel length, pre-heating should have no effect except to allow an increase in flow rate.

Even if the thermoblock is sufficiently thermally responsive to allow PID control to work (a BIG if) you'd still get more control ex the pump than the PID.

Alan

Alan Frew wrote:Given sufficient block heating and channel length, pre-heating (of incoming water) should have no effect except to allow an increase in flow rate.

Flow rate is a constant.

Scenario #1
Input temperature is variable. Flow is a known constant.
Thermoblock might have to really crank out the heat to bring the water to target temperature. You'd want to PID the block to prevent overshoot.

(Aside: The longer the channel the less dramatic the block's energy increase would have to be, so you could also make a longer block to improve performance.)

Scenario #2
Input temperature is a known constant. Flow is a known constant.
Thermoblock does not need to vary its energy if it has been designed to expect a known input temp and flow rate. No need to PID the block: you PID the pre-heater.

If you're going to PID the pre-heater, do you need the block?
Only if preheating water to less-than-brew-temp and then using the block to bring it the rest of the way, on an as-needed basis, is cheaper than keeping several beverages-worth of brew-water at brew-temp.

Hi guys,

the flow rate is constant in a thermoblock as the flow from the group is constant. That's of course assuming we are not messing with the flow, ie. the machine hasn't got pressure profiling.

Given sufficient block heating and channel length, pre-heating should have no effect except to allow an increase in flow rate.

No effect? the thermoblock when constantly on will raise the temperature of the entering water and the delta between Tin and Tout will be dependant on the length of the thermoblock path (contact time with hot surface). If you supply warm water warmer water will exit, which was one of the reasons my friend added the pre-heating boiler.

Actually mixing the hot-cold water might be a nice solution as it means less hassle with the heaters. There's still the problem of heat loss/gain through the group but that could be partially eliminated by having it heated by a dedicated heater and keeping the mixing block quite close to the group. The machine would also have to be a DB as this method needs a source of hot water which is kept at a steady temperature level.

Regards,
dsc.

timo888 wrote:Simply measuring shifts in brew-ratios ("solids yield") will tell us very little about the effects on flavor of various pressure profiles. As the article from U.C. Davis states, some compounds have no impact on flavor. Others that do have profound effect on flavor evade measurement because they're active at a few parts per trillion....

1. If you think that brew ratios and "solids yields" are the same thing, you simply don't understand the subject.
2. The article from U.C. Davis is about wine. This may come as a shock to some people, but...wine and coffee are NOT the same beverage!. Using a wine article to "prove" a point about coffee proves very little (IMHO).
3. "Solids yield" (or "solubles yield") is not the whole story, but in brewed coffee as well as espresso it is an essential part of the story. This would become evident if people stopped with their theories and their whining and actual TRIED the technology.

timo888 wrote:A reduction in pressure that results in a lower solids yield could well preserve aromatic compounds that disappear when the pressure is increased, and/or an increase in pressure might increase the amount of solids that result in flavors that are not liked....

Crucial to your point are the words "could" and "might."

Nick at Murkycoffee wrote:... measuring a quantity of solubles is a far cry from measuring the quality of those solubles. ... It doesn't tell you whether those solubles were the (predominantly) kind that you want, vs. the kind you don't want. ...

Skeptical Nick has said that he's purchased an ExtractMojo setup, so hopefully we'll hear from him about it soon.

[DAN-- MAYBE THE SUB-THREAD STARTING A FEW POSTS BACK WITH GREG's COMMENT ABOUT PRESSURE COULD BE APPENDED TO THE REFRACTOMETER THREAD??]

My fault for not stating it as clearly as it could or might be stated, Andy. My intention was not to dismiss refractive index as a potentially valuable tool, but merely to offer certain caveats.

If I understand correctly, the question, as it relates ultimately to pressure profiles, is twofold:

a) does refractive index correlate with flavor(s) in espresso?
b) do different pressure profiles produce different refractive indices in espresso?

The only way to answer the first question is to correlate refractive index data with the observations of a panel of tasters. This would have to be done against a decent variety of roasts/blends/varietals/temperatures if it is to have general applicability. The second question can be simply answered by running the tests in a) against some different pressure profiles. Simple in terms of lack of complexity, but difficult in terms of the sheer amount of simple work that would have to be done.

The caveats:
If flavors in espresso correlate with refractive index, that does not mean that the correlation is unambiguous. As Nick suggested, you might have two cups of espresso with the same refractive index, where one tastes good and the other not so good. To paraphrase Nick: the espresso police couldn't come into your shop and take some refractive index measurements and give you a seal of approval.

Nor does it mean that flavors correlate only with refractive index. They could correlate with volatile elements detectable only via gas chromatography or, as the article on wine indicated, with molecules that evade measurement because they have effect in tiny tiny tiny quantities. Tea bush, grape vine, coffee tree all have things in common with respect to flavor molecules; you cannot dismiss the article on wine as irrelevant; it's about the challenge of measuring more or less tangible elements that affect the perception of flavor.

timo888 wrote:a) does refractive index correlate with flavor(s) in espresso?
b) do different pressure profiles produce different refractive indices in espresso?

Timo, you still don't understand the basic concepts.

Refractive index (ie, espresso strength) and solubles yield are NOT the same.

There is NO correlation between refractive index and flavor in espresso.

There is a strong correlation between solubles yield and flavor in espresso.

You could try rereading my post that Greg cited, or you could read this SCAE publication for a clearer explanation. The SCAE presentation is about filter coffee, but much of the basic science behind brewing coffee is the same whether it's drip, Aeropress, cupping, espresso, or filtered through a clean gym sock.

The strong correlation that I'm claiming above is mostly about the balance of sour and bitter flavor, and also about revealing the sweetness and distinctive character of a given coffee. The sour/bitter balance is crucial for a good coffee no matter what the prep method.

I understand that there are many other flavors that bring joy or pain in espresso, but the refractive index/solubles yield approach probably can shed no light upon them. In other words, it's extremely difficult to measure grossly channeled shots, stale flavors, dirty machines, rioy beans, Ethiopian blueberry, etc, with this technique.

As far as analyzing the effect of different pressure profiles on espresso, I really don't know the answer.

Andy, even as you've narrowed it down, the dissolved solids affects two dimensions: sour/bitter , and sweetness. I guess the more dissolved solids, the more bitter and less sour.

But as a novice it's not obvious to me where to go to get sweetness and distinctive character. Does that depend on what character I like from the coffee, so that to get the blueberries, I have to accept sourness, from a particular coffee?

This thread reminds me of the Crossland Espresso Machine Project thread on CoffeeGeek, a project to make a machine that can profile temperature and pressure and mixing different temperature waters and lowering the mass of the group have both been discussed.

It is an interesting idea and the Crossland thread has gone into a quiet phase lately. The finished products of either of these projects may not appeal to fans of classic "heavy iron" espresso machines.