Wireless brewing temperature sensor

I'm planning to build a wireless temperature sensor to assist someone in their hobby, brewing beer. Periodic temperature report is all that's required, no control at this stage.

I bought the NRF24L01+ kit, so the next steps are:

• Finding a temperature sensor suitable for immersing in liquid (with a sterilised cover)
  
• Working out how to power the Espruino for (at least) a few days. I have a few old phone handsets so I'm hoping to use the batteries. There is no mains power where the beer is fermented.
  
• Working out whether I need to use the other Espruino to receive SPI and communicate over serial to a linux machine. Ideally, I won't need to do this and can use SPI directly from the linux machine.
  
  

As you can see, the plan is very rough so far. And I haven't used SPI before so I'm not sure of the range or what I'll need on the linux side.