Featured Project
# Instant Nitro Cold Brew Machine
Team Members:
- Mihir Vardhan (mihirv2)
- Danis Heto (dheto3)
# Problem
Cold brew is made by steeping coffee grounds in cold water for 12-18 hours. This low-temperature steeping extracts fewer bitter compounds than traditional hot brewing, leading to a more balanced and sweeter flavor. While cold brew can be prepared in big batches ahead of time and stored for consumption throughout the week, this would make it impossible for someone to choose the specific coffee beans they desire for that very morning. The proposed machine will be able to brew coffee in cold water in minutes by leveraging air pressure. The machine will also bring the fine-tuning and control of brewing parameters currently seen in hot brewing to cold brewing.
# Solution
The brew will take place in an airtight aluminum chamber with a removable lid. The user can drop a tea-bag like pouch of coffee grounds into the chamber along with cold water. By pulling a vacuum in this chamber, the boiling point of water will reach room temperature and allow the coffee extraction to happen at the same rate as hot brewing, but at room temperature. Next, instead of bringing the chamber pressure back to atmospheric with ambient air, nitrogen can be introduced from an attached tank, allowing the gas to dissolve in the coffee rapidly. The introduction of nitrogen will prevent the coffee from oxidizing, and allow it to remain fresh indefinitely. When the user is ready to dispense, the nitrogen pressure will be raised to 30 PSI and the instant nitro cold brew can now be poured from a spout at the bottom of the chamber.
The coffee bag prevents the coffee grounds from making it into the drink and allows the user to remove and replace it with a bag full of different grounds for the next round of brewing, just like a Keurig for hot coffee.
To keep this project feasible and achievable in one semester, the nitrogenation process is a reach goal that we will only implement if time allows. Since the vacuum and nitrogenation phases are independent, they can both take place through the same port in the brewing chamber. The only hardware change would be an extra solenoid control MOSFET on the PCB.
We have spoken to Gregg in the machine shop and he believes this vacuum chamber design is feasible.
# Solution Components
## Brewing Chamber
A roughly 160mm tall and 170mm wide aluminum chamber with 7mm thick walls. This chamber will contain the brew water and coffee grounds and will reach the user-set vacuum level and nitrogenation pressure if time allows. There will be a manually operated ball valve spout at the bottom of this chamber to dispense the cold brew once it is ready. The fittings for the vacuum hose and pressure sensor will be attached to the screw top lid of this chamber, allowing the chamber to be removed to add the water and coffee grounds. This also allows the chamber to be cleaned thoroughly.
## Temperature and Pressure Sensors
A pressure sensor will be threaded into the lid of the brewing chamber. Monitoring the readings from this pressure sensor will allow us to turn off the vacuum pump once the chamber reaches the user-set vacuum level. A temperature thermocouple will be attached to the side of the brewing chamber. The temperature measured will be displayed on the LCD display. This thermocouple will be attached using removable JST connectors so that the chamber can be removed entirely from the machine for cleaning.
## Vacuum Pump and Solenoid Valve
An oilless vacuum pump will be used to pull the vacuum in the brewing chamber. A solenoid valve will close off the connection to this vacuum pump once the user-set vacuum pressure is reached and the pump is turned off. To stay within the $100 budget for this project, we have been given a 2-Stage 50L/m Oil Free Lab Vacuum Pump on loan for this semester. The pump will connect to the chamber through standard PTFE tubing and push-fit connectors
If time allows and we are able to borrow a nitrogen tank, an additional solenoid and a PTFE Y-connector would allow the nitrogen tank to connect to the vacuum chamber through the same port as the vacuum pump.
## LCD Display and Rotary Encoder
The LCD display allows the user to interact with the temperature and pressure components of the brewing chamber. This display will be controlled using a rotary encoder with a push button. The menu style interface will allow you to control the vacuum level and brew time in the chamber, along with the nitrogenation pressure if time allows. The display will also monitor the temperature of the chamber and display it along with the time remaining and the current vacuum level.
# Criterion For Success
- A successful cold brew machine would be able to make cold brew coffee at or below room temperature in ten minutes at most.
- The machine must also allow the user to manually control the brew time and vacuum level as well as display the brew temperature.
- The machine must detect and report faults. If it is unable to reach the desired vacuum pressure or is inexplicably losing pressure, the machine must enter a safe ‘stop state’ and display a human readable error code.
- The reach goal for this project, not a criterion for success, would be the successful nitrogenation of the cold brew.
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