Vac pot brewing - I.


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There are a lot of different vac pots & if you have a look at my little collection, you may understand that each has its own particularities. Shape, size & type of filter determine how you can get the best brew from a vac pot.

Part I. - Grind & Timing

These are the two interrelated variables you can, or, rather, should play with to get the best brew from your vac pot. A third variable is the amount of coffee. Normally you will use the same amount as with other infusion methods, but there may be reasons to use a bit more.
I posted the bit below earlier in alt.coffee, but since it's a good description of the variables, I'll put the slightly revised version up here.

1. There's no prescribed steeping time - it depends on a number of variables, amongst which, probably most important & easiest to control, the grind size. Simply put: large grains need long steeping, while a short contact time suffices for finer grind. Roast colour & freshness also play a role, but their effect on steep time are marginal.

2. Grind size is in part determined by the sort of filter - to prevent clogging some vac pots (eg. Santos & some using mesh filters), using a coarse grind is preferred. Cloth filters & glass drainers can usually handle a pretty fine grind. Though some filters won't clog, they may allow more sediment in the cup when grinding very fine - how much "mud" you can tolerate is up to you, of course.

3. Contact time is also in part dependent on the shape & size of the lower bowl; one thing you do definitely *not* want, is to let the jug boil dry - it will die on you. Sad, but true.
IOW, you can let it boil until (shortly before) it runs dry - this is the upper limit of the contact time in glass vac pots & in small vacs ("3-cuppers", or smaller) it can be a very important limit! Shape & size can thus actually determine steep time & thereby grind size. Spherical lower bowls leave less water in it than flat bottomed ones & will, thus, have a shorter maximum contact time. Another factor is the distance between bottom end of the siphon tube & the bottom of the vac - a smaller distance means less water left downstairs & hence shorter steeping.

4. One category of vac brewers, the automatics, may need special treatment - some of these (including both the Sunbeams, Utopia/e-Santos et. al. & the balancing vacs such as the Royals, Cafetinos & Percos), have a preset, non-adjustable contact time. In this case there are only two ways to get the best cup: tune the grind (not clogging the filter & not leaving too much sediment) & maybe even the amount of coffee (my pref is about 14-ish gram per 250ml mug).

5. The water left "downstairs" dillutes the final brew - simply put; more water = weaker brew. This is why you can't get an acceptable brew using only half the vac pots capacity; it will just be watered down too much. With some vacs (I have one), there's almost too much water downstairs to even get a decent brew with a full load. Still, if you're not using an automatic vac, you can adjust the amount of dillution a bit by letting the vac boil slightly longer, since this causes some of the water to evaporate. The rate at which this happens depends on how high a flame you're using.
As per 1. you should use a coarser grind in this case, since you actually want a long steep. Note: it is a bit dangerous to explore the limits of this & you may accidentally kill your vac pot. Your choice: no responsibility accepted by yours truly...

Still with me after all that?

Ok, try this then. With glass vacs, the simplest rule of thumb is to consider the brew time fixed & somewhere in the 'hood of three minutes (but do keep watching the amount of water downstairs!) Using filter drip grind will usually work ok with this. Note: again, in a small vac with spherical lower bowl, the max. steep time may be only *ONE* minute, in which case you should use a fine grind.

From there, once you get a feel for the process, fine tuning isn't too hard. Simply grind as fine as the filter will allow (might take some trial & error) & shorten the steeping time accordingly - let your tastebuds guide you here.

If you have a good grinder (ie. one that doesn't produce much dust) & you don't get too much sediment in the cup, you may indeed get the brew time down to only 90-ish seconds, or maybe even slightly less for darker roasts.



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