Let's say that the roaster of the espresso blend you are using recommends a temperature of 92C for an 18g dose. If you wanted a single espresso using 9g of coffee, would you adjust the brew temperature? If so, up or down?

Matt

Maybe. Maybe not. Start with the recommended, taste, and decide for yourself.

**Due to basket shape and all manner of funky things, a single shot of what was calibrated at 18g may or may not be 9g. Flow rate is different, extraction is different, resulting taste is different.

John P wrote:Maybe. Maybe not. Start with the recommended, taste, and decide for yourself.

I can certainly do that. I was wondering, however, whether there is a general principle involved - if so, that would save time dialing-in new coffees. As single baskets are designed to allow you to keep the brew time the same, the principle variable would seem to be hot water penetrating a deeper, heavier puck or a thinner, lighter one. Intuitively, I imagine the larger puck would require more heat to bring it up to brew temperature than would the smaller one. And, therefore, you would need hotter water for the double than the single. But I'm no physicist.

Matt

mathof wrote:Intuitively, I imagine the larger puck would require more heat to bring it up to brew temperature than would the smaller one.

I've never measured either, but given that specific heat of water is ~2.5x that of wood (according to this table) and coffee is mostly wood-like cellulose, I doubt 9 grams of coffee would make a measurable difference in the temperature profile. As I noted in Can hot portafilter burn the coffee even before brewing?, even hot/cold baskets don't make as significant difference as you might think:

HB wrote:Years ago I did measure the temperature difference between the top and bottom of the puck for hot/cold baskets:



The distance between the lines indicates the cold/hot basket delta; the distance from the 0 axis represents the top/bottom delta. It shows that indeed cold/hot baskets do have a measurable effect on the first seconds of the delta between the top/bottom, but the effect falls below the boiler's natural temperature variance shortly thereafter (measured on a La Marzocco Linea without PID controller).

From Can hot portafilter burn the coffee even before brewing?

- Let us compare a double shot with a single one in a La Marzocco-like basket. Given that, the ratio of the surfaces of the pucks is exactly 2 (because 58^2 / 41^2 = 2).

- Let us divide by 2 the dosage for the single shot.

- Let us suppose there is an opv (if not, what follows is not true). Then, if we want the extraction time to be the same, the grinding size should be the same. In this case, the thickness of the pucks is the same.

- Given that, the water flow in the puck will be divided by 2 for the single basket. Thus, the amount of water per gram of coffee powder is the same. Now, to bring the same amount of heat from this amount of water to a gram of coffee powder, we need equal temperature of extraction.

To summarize, the double shot is expected to be identical to the single one, with double volume.
As you say mathof, I also think that one needs to bring more heat when the weight of the puck is doubled, but this is done in the above case by doubling the water flow, while keeping the temperature the same.

Of course, all that is not exactly true if one uses a 58mm single basket... Personally, I keep the temperature the same in this case too.

PS: just for fun... one can also mention a word about tamping:

To expect the same shots with the 58mm double basket and the 41mm La Marzocco-like single one, one should also keep the same tamping. This means that the pressure imposed on the pucks should be the same. But pressure is not force: Since a force is a pressure times a surface, in order to have identical pressures on the pucks, one needs a double force imposed by the barista on the 58mm basket.

Eg: 15kg on a 58mm basket is equivalent to 7.5kg on a 41mm one.
In other words, 15kg on a pavoni, arrarex or LM basket is enormous... and has probably some (bad) effect on the result in the cup (?)

Tamping pressure hasn't really stood up to testing as particularly important. Your analysis is interesting but puck compression likely has a threshold of pressure required and after that, once most of the air is gone, the rest is merely wasted energy.

another_jim wrote:If you use the same grind, and adjust dose to get the same relative flow rate (same brew ratio in the same time), you'll get the same extraction and cooled off taste from any basket. But ... the hot taste and mouthfeel will still vary from basket to basket. It's best to try a lot of them and pick a favorite.

That's interesting. I wonder if it explains why two singles made from 18g in a double-spouted basked tastes so different from a single-shot prepared with 9g in a 41mm basket. (Same relative flow rate)

Matt

In the spirit of what you say:

I always find surprising the fact that a double shot in a single cup does not have the taste of the same double shot divided in 2 cups. Each time I made the comparison, I found the shot divided in two cups better. In this case, the factor raised by Jim is clearly relevant: if we wait enough... we expect getting the same drinks once everything is at the same temperature (cups+drinks). However, when the coffee arrives hot in the cup(s), its temperature is clearly lower when served in 2 cups.

Another effect maybe the % of crema we drink : when the double shot is in a single cup, the crema has a double thickness and we drink most of it first. After that we drink most of the liquid coffee. On the contrary, when we drink the same shot in two cups, we drink crema and liquid at the same time. This gives a very different mouth and taste feeling.