Halve <quantity>1</quantity> lime

Squeeze the lime juice into a jigger to measure <quantity>15<unit>ml</unit></quantity>

Separate <quantity>½</quantity> egg white from <quantity>1</quantity> egg and reserve the remaining for other preparations

Fill a coupe glass with ice cubes and let it rest to chill

Fill a cocktail shaker with ice cubes

Add the egg white

Add the lime juice

Add <quantity>1<unit>tsp</unit></quantity> of sugar

Add <quantity>30<unit>ml</unit></quantity> of white grape juice and <quantity>45<unit>ml</unit></quantity> of bourbon

Put the lid on and shake it vigorously until thoroughly chilled

Discard the ice cubes from the coupe glass

Sieve the liquid into the chilled glass

Cut <quantity>1</quantity> small slice of the lime peel

Express the peel over the cocktail

The Grape & Sour is ready! Cheers!