How can I improve this Chemex cold brew method? I do like my cold brewed coffee but it's difficult and inconvenient for me to make and keep in work due to the time it takes to steep, shared fridge space, etc. 

I came across this method recently...


  The iced method isn’t complicated. Basically, you prepare brewed coffee as you normally would, only you use half hot water, half ice you put in the bottom of the vessel. The hot, fresh coffee drips directly onto ice so that it’s cool and ready to drink right away.


I've now tried it a few times using my small chemex and a ratio of 2:1 (water to ice) rather than 50:50. I'm trying the pour over much more slowly than I normally would to maximise the extraction while using less water.

I can't really fault the taste, the flavour is still great, the finish is less acidic but obviously more watery. So while this method is indeed quick and uncomplicated I'm curious about 2 things:


What else can I do to compensate for the extraction difference? I would really prefer it to be less watery.
Am I potentially going to crack the pot with the combination of hot and cold? I can't find any info on temperature variances on the Chemex site. 


Edited to add information...

For a hot-brew I normally use  using 300ml hot water for 21g of grind. Here I'm using 200ml hot water in the pour over, to compensate for the 100g of ice that melts. 

I'm taking 6-7 minutes with the pour. Normally I would take 3 minutes.

I'm making my grind slightly finer in order to extend time it takes the water to drip through. I would consider it to be medium-fine.
What you're talking about is the "Japanese iced coffee" method, which is hot-water brew directly over ice. In contrast, cold-brew is using cold water in contact with the grounds. See techniques at other questions tagged as cold-brew.

This article from Counter Culture, also referenced in the article you linked, suggest Japanese iced as an alternative to cold brew. The articles suggest that directly brewing hot coffee over ice retains more of the volatile flavour compounds.

If you have had true cold-brew before, most methods use several times as much coffee grounds to brew as with other methods (some then dilute this with, e.g., water or milk). For example, normalized to a 200mL "cup" (~6.5 fl.oz.) of brewed coffee: Blue Bottle suggests about 3x more coffee for cold brew (45g per 200mL) than for drip (14g per 200mL). If you're coming from that strength, it's no wonder you're finding it watery. 

To your first question: If you want a stronger brew, why not simply use more coffee grounds? Your amount (21g grounds to 300g water+ice is about 14g/200mL cup) is already at the higher end of the spectrum for drip coffee; the industry standard is closer to 7g per cup/dose. But if you want it stronger, use more beans!

On your other question: this temperature change shouldn't be an issue. You said you're using a Chemex (e.g., classic 3-cup) -- it is made from Pyrex brand borosilicate glass, which has very good thermal shock properties. Even a lesser glass (e.g., non-tempered soda-lime glass) shouldn't be a problem at these temperatures (slowly dripping boiling water onto ice). (However, for example, ice into glass at oven temperatures could certainly be a problem).