Set Offset without Scace

[timbo]

I don't have a Scace temperature device, like most people, but I think I came up with a procedure for accurately setting your brew boiler offset without one. I did this procedure on my newish Vivaldi II S1 plumbed in version.

For a bit of a background, for those not familiar with temperature offsets - the Vivaldi II S1 comes with a single temperature sensor located in the brew boiler. Obviously, as you are pouring a shot, the water will change temperature. You can set the difference between the boiler temperature and the temperature at your group (ie. the temperature of the water hitting the coffee) using the programmable features of the S1. The procedure for setting it is in the manual.

The problem with the S1 is that you have a 'precise' measurement of the temperature in the boiler, but you don't have an 'accurate' measurement of the water exiting the group. The programming of the S1 allows you to change the offset temperature from -8 to +8 degrees C, which is quite a bit. The problem is that unless you have an expensive 'Scace' thermofilter (a portafilter customized with a thermocouple for taking precise measurements of the water exiting the group), you can't set this accurately.

Until now. This procedure relies on the fact that water boils at 100C normally, and boiling water exiting a group is fairly easy to notice. Those of you who live at high elevations will probably want to modify this to the fairly well known local boiling point.

Here's what I did:

1. Turn off any pre-infusion. If you've got the chamber, maybe you want to remove it.

The idea here is to get the water into the group as fast as possible from the boiler.

2. Take note of current temperature offset.

In case it doesn't work, you can return to where you where.

3. Set your Brew Temperature to 97*C (maximum)

This is the temperature displayed on the front of the machine in normal operating mode. We want to set it to the maximum. As we'll see in a second, our goal here is to get boiling water out of the group (which is 100C).

4. Go in and set your Temperature Offset to -8C

5. Purge you brew boiler.

A quick note on purging. In order to really check the water in the boiler, it is necessary to pull some shots and observe the temperature drop below your current set temperature (which should be 97C), then let it recover. The idea here is that as soon as the boiler recovers, you can be guaranteed that the temperature is stable in the boiler then you can test it. You should perform this purge every single time you change the temperature, and make sure you let it fully recover before proceeding.

6. Remove your portafilter handle, and pull a shot and look for water boiling out of the group.

It should be boiling, you have set your machine to it's maximum possible temperature. It's pretty easy to determine whether or not the water is at or above 100C - it will be sputtering out of the dispersion screen with loads of steam.

7. Now you want to find the offset setting exactly where the water stops sputtering.

I would suggest doing a 'binary search' for it. Try an offset of 0C, and if it's still sputtering go into the positive offests, otherwise, keep narrowing it down until it's hot enough so that the next higher setting will make it sputter.

Congrats - you've found the offset that sets your group to 100C.

8. Your actual temperature setting on the machine is 97C - so you are going to need to adjust your offset by -3C in order for your main temperature to be accurate.

9. Go ahead and reset your pre-existing pre-infusion options.

NOTE: I did not test this technique against a Scace device, though I did test it against taste of beans that I know to perform in a certain range (which is, of course, very unscientific). If someone has access to a Scace device, I would appreciate it if they cross referenced this technique to the results on the device and let us know how it compares.

[Dan Bollinger]

That's a nice bit of thinking. I'm going to save your technique.