Pressurised Cold Brewing

August 20th, 2010

I read quite a lot of blogs. Actually that is probably a half truth. I subscribe to a huge number of blogs and often skip through postings that don’t immediately grab me. This one I read, and it lead me to this post.

I’m sure it is no leap to see where I am going with this, and also clear that I am not claiming this as original thinking!

I began to wonder if pressurised brewing could be applicable to more than espresso. Cold brewing (not icing hot coffee to dilute, but brewing with ambient/cool/cold water) is often a little disappointing. While you can get a balanced and tasty brew you sometimes miss out on some of the interesting aromatics and flavours, as well as the acidity, of some coffees – due to a lack of heat/energy to extract them.

Could pressure add the necessary energy – perhaps even allow rapid cold brewing?  I loaded a syphon with 15g of coffee and 250ml of water, pressurised it, shook vigorously and then waited a minute and released the pressure.  I strained it through a V60 and tasted it.  Disgusting, barely any extraction.

“More time….” I thought – so I set up a longer brew.  The results were very tasty.  I needed a control sample, so last night I experimented again.

The two brewers

I would use the same amount of coffee, water and use the same brew time.  One brew would be in a french press, left to steep.  The other would be pressurised.

Matching doses within 0.1g

For the coffee I used a test batch of the washed lot from Finca Killimanjaro, from Aida in El Salvador.  We’d already cupped it and I knew it to be juicy, tasty and not an obvious coffee to (traditionally) cold brew.

There is a lot less bloom with cold water.

I steeped them for 12 hours – the french press lidded and two charges into the cream whipper.  (If anyone knows how to calculate how much pressure the liquid was under I’d be very grateful!)

This morning I strained the two coffees in preparation for serving to the rest of the team at the roastery.  The french press brew looked fairly normal:

Straining the press pot

Straining the pressurised liquid was very different.  Overnight the gas had gone into solution and releasing the pressure meant that it began to bubble and fizz out (this is important – more on this later!).  It doesn’t look very appealing to pour a mass of fizzing coffee slurry into a V60!

Fizzing coffee slurry

The coffee also looks a little odd initially as I think it was still giving up a little of the dissolved gas.  Very quickly it just looked like paper filter coffee again.

Pressurised cold brew coffee

I served the two coffees blind to everyone, though it was clear there was an obvious winner.  Everyone picked the pressurised brew as being more delicious.  I checked the extractions with the Mojo and the preference made sense.  The ambient pressure cold brew struck out at a lowly 14% extraction.  The pressurised brew (with identical time, brew temp and grind size) came out at 18%.  This was a pretty significant change to the brewing process.

Now – I know what you are thinking:  Is the pressure speeding up the extraction.  My initial thoughts are:  probably not.

I think that the aggressive fizzing upon depressurisation and during the pouring process was effectively and noticeably agitating the coffee grounds increasing the extraction.

What I’d like to try next is to compare an ambient cold brew that gets up to 18-19% extraction (into the zone of deliciousness) to a pressurised brew of equal extraction.  I’ll probably need to agitate the coffee in the ambient brew to get it to do that without introducing a new variable between them of brew time.  This should also give a slightly clearer impression of the role of pressure outside of its agitating effect.

The coffee:  pretty damned tasty – and some nice acidity/juiciness in the cup which makes me hopeful.  We did it with one of the Kenyas we have (the Tegu AA lot) and it was seriously delicious.  If any of you have a cream whipper and some spare time and want to experiment too I’d love to hear about it.  Thoughts, suggestions and gentle berating for silly experiments always welcome in the comments!

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