Something that is perplexing me at the minute is the temperature of the coffee coming out of my Bacchi. I measured it today and it was 50c (122F) which means that in theory it has dropped 40c (72F) on its journey from the boiler to the cup.

Has anyone measured the temperature of their coffee this way, and does this sound about right?

Ian_G wrote:Has anyone measured the temperature of their coffee this way, and does this sound about right?

Not exactly what you asked about, but there is some relevant data here.

HB wrote:It depends on how you measure since water temperature falls like a stone. It also depends on how much water is drawn through the coffee (more water, higher final in-cup temperature). As a rough guideline, espresso temperature is typically around 165°F in the cup immediately after brewing.

Not being very scientifically minded my, ahem, data is probably not all that useful. Looking at the way the Bacchi works (and maybe it's the same with other machines) the coffee basket sits in, what is effectively, a massive heatsink. So as the water leaves the boiler, heat is absorbed immediately into the surrounding metalwork.

I have a heat gun and feel another "experiment" is in order.

I have had a go with the heat gun. On its lowest setting it blasts out air heated to 300 c (572 f), so I knew I had to exercise some care. I targeted the top of the Bacchi where the basket is held and it took about 3 minutes or so to get the outside metal temperature to 70 c (158 f). I timed it so that this temperature was achieved just a few seconds before the extraction.

The coffee temperature coming out was now 68 c and was letting off little wisps of steam, which it had never done before. So that was an increase of 18 c (64 f) on an unheated effort.

I wish I had never done it. The reason being that, not only did the coffee have more body and a subtley better flavour, but it smelled delicious. Maybe it was a fluke - I need to try again to make sure. But what a revelation. If it works again then I'm going to be stuck with the heat gun method, which is not exactly ideal. I had mostly been expecting to get a burnt taste but there was no hint of it. So I'm both delighted and pissed off.

Marvelous.

You could leave the Bacchi whistling for say another minute while the water continues to heat and you'll still get 9 bar but the water will be hotter. The coffee will be be scalded by that point and will spatter all over the place and taste terrible.

But there appears to be some opportunity to control extraction temp by letting the Bacchi sit longer on the heat source. The question is how much and to what effect. That I do not know, but the option is there.

My question is: by the time the Bacchi whistles (say around 6 minutes), how hot is the aluminum assembly around the basket? I imagine it would be above 100C by that point, so I wonder if it would really be a heat sink. Perhaps some testing is in order?

Dom

coffeedom wrote:... But there appears to be some opportunity to control extraction temp by letting the Bacchi sit longer on the heat source. The question is how much and to what effect. Dom

My first attempts at using the Bacchi often resulted in the machine sitting on the heat longer than was optimal and this resulted in a burnt and bitter taste.

coffeedom wrote: My question is: by the time the Bacchi whistles (say around 6 minutes), how hot is the aluminum assembly around the basket? I imagine it would be above 100C by that point, so I wonder if it would really be a heat sink. Perhaps some testing is in order? Dom

It was measuring the outside temperature of the assembly that started me wondering in the first place. When I first measured it, it was around 60 c (140 f). Obviously once the water has been pushed through the basket it is a lot hotter, but pre-infusion it sits around the 60 c mark.

The metal to metal join between the boiler assembly and the group head has a very small surface area and so the potential for heat transfer from the bottom half to the top is restricted. Obviously there is heat transfered from the boiler water below the base of the group, but the base will always be cooler than the water.

As the water is supplied from the boiler to the basket from below, its first contact is with the base of the group head, which is both large in area and thickness, so if the base is cooler, then the water temperature will immediately fall prior to being pushed through the coffee. In my view the answer is not to make the water hotter, but to make the housing for the basket warmer, so that the temperature differential is markedly reduced.

The heat gun method is Heath Robinson and clearly imprecise. However I have found the effect to be good and surprisingly consistent. The taste improvement is subtle and hard to define. What's clear is that both the body and the aroma improve significantly. It's amazing just how much these two factors contribute to the enjoyment of the drink.

Subjectively this has taken my espresso from enjoyable to very enjoyable. What I think I need to do now is push the heat some more and get the group head up to 90 c and see what happens. If it makes the coffee worse at this temperature then I'll still be damn pleased with what I've done.

The more elegant solution would be to have a heating element collar that would pre-heat the group head to the best temperature.

OK I'm now in a position to make a recommendation. My tip for Bacchi owners is to buy a heat gun (£30ish), if you've not already got one, as it will easily add about £250 to the value of your Bacchi.

The method I used was to set the heat gun at the lowest setting (300 c) and "paint" the heat on to the bottom half of the group assembly. Hold the gun about 2 inches away from the target and apply even heat around the group during the last 4 minutes. To check if you're in the ballpark heat-wise, measure the temperature of the coffee in the cup. It should be about 70 c. Failing that if you get wisps of steam coming out of the cup and it is still cool enough to sip, then I'd say you're there. One other measure you can look for is those fancy stripes everyone talks about in your crema. The crema should also have a just noticeable reddish hue.

What if your coffee tastes really, really, good using the Bacchi as it was designed?

If it aint broke don't fix it. You don't have to try it.