# Real Labs (/en/docs/labs)



Each lab changes exactly one variable and keeps everything else constant. When you finish, write down what you tasted in the lab log below.
If you can also explain in your own words *why* it changed, you have really understood the concept.

## How to run a real lab [#how-to-run-a-real-lab]

<Steps>
  <Step>
    **Predict first.** Before brewing, write down which cup you expect to be more sour, more bitter or stronger.
  </Step>

  <Step>
    **Change one variable only.** Apart from the item under “Change only”, keep everything the same: same coffee, same dose and water, same technique.
  </Step>

  <Step>
    **Taste side by side.** Let the cups cool to a similar temperature, go back and forth, name the difference first, then decide which you prefer.
  </Step>

  <Step>
    **Record it, then plan the next step.** Write down the result and taste, then pick exactly one variable to change in the next cup.
  </Step>
</Steps>

Records are stored only in this browser on this device. They also appear in the [Brew Log](/docs/brew-log); review and export them there or in [My Progress](/docs/progress).

## The six labs [#the-six-labs]

<LabIndex />