I do a sink shot on the Expobar Office Control after an overnight rest. However, as the machine is only fired up for making 3 or 4 doubles daily, should a sink shot be performed prior to each one? There is about a 6 hour spacing between drinks.

A sink shot is usually done after cleaning the machine (bakcflushing, soaking PF in detergent etc). You don't need to do a sink shot every time you fire up the machine. Just make sure to give it a proper warmup and you should be fine.

Now another discussion is the need to do a sink shot after a cleanup.The thought is that all the exposed metal needs to be "seasoned" with coffee oils in order not to give the drink a metallic taste. James Hoffmann make a good case for why this is not needed. He argues that most likely the first shot tastes bad because the water is no longer at desired temperature (due to extensive flushing), the portafilter might have been left out of the machine for a while etc.

An espresso machines inner workings are all exposed metal. The water that travels through it does not pick up any metallic taste. Why should it do so inside the basket just because there is some coffee there as well?

My guess is that if you leave the machine to heat up properly after the cleanup you should not have to sink the first shot either.

I throw out the first shot of every session, simply because I'm too lazy to purge my grinder from the last session and it's one way to dispose of those now-staled grounds, and also it seems that running one shot after my flush from idle routine seems to equalize temps at the group.

Another theory I read here is that some don't clean their dispersion screen as well, leaving coffee to cook on there during idle times... and therefore making a 'sink shot' can help.

I clean mine with a group brush after every shot, and backflush (with water) frequently... so I don't find there's much difference in quality between first and consecutive shots.

EBSpokane wrote:I throw out the first shot of every session, simply because I'm too lazy to purge my grinder from the last session and it's one way to dispose of those now-staled grounds, and also it seems that running one shot after my flush from idle routine seems to equalize temps at the group.

If all you want to do is purge your grinder and get to the fresh beans, why not grind for a few seconds and throw the stale grounds in the waste? And you can run a couple ounces through your machine without the PF to get your machine to the proper temp. This seems easier than going through the process of making a shot. Or am I completely missing your point here? It just sounds like you are making a shot just to purge a few beans.

Controversial subject.

Have a look at: Sink that First Shot