Ask HN: How does Google customize Search based on recent searches

Example: say you start a search on Google.com for "garage epoxy flooring". Then for subsequent searches Google is able to change the auto-suggest based on context of recent searches. If you type "best colors" the Google auto-suggest will show "best colors for garage epoxy flooring". In addition to auto-suggest Google also customizes the search results based on recent context. If I just type "best colors" then Google shows epoxy flooring colors.

It seems like Google is able to infer the context of Search and then user it to customize behavior in subsequent searches. I want to implement something similar to guide users of my app (It helps users find right gifts etc.)and I am curious if there is a specific tech Google uses to implement such customization.