Do not interpret 'keep in touch' as a hidden promise of a referral. It is an invitation to maintain the relationship, not necessarily to ask immediately.

Reconnect when you have a natural reason, such as an application opening, an interview invitation, or a meaningful update related to the conversation. If the relationship has developed, asking whether they would be comfortable referring you can be appropriate.

Make it easy for them to say no. A direct but low-pressure request is usually better than repeatedly hinting. If useful, this guide on consulting coffee-chat questions gives more detail.