You cannot build two rail links in a single Network action during the Rail Era if there is not enough beer available to pay the required cost for both links.

Explanation

• On page 12, it states:
  "If you performed the Network action to build rail Link A, it would be possible to build a second rail Link B in the same Network action (as long as you could pay the required cost, and consume the necessary coal and beer)."

• This means that each rail link built during the Rail Era requires you to pay the cost and consume the necessary coal and beer. If you do not have access to enough beer for both links, you cannot build both in a single action.

• There is no rule in the provided context that allows you to ignore the beer requirement if it cannot be met.

Source: page 12

Summary:
You may only build as many rail links in a single Network action as you can pay for and for which you can consume the required coal and beer. If there is not enough beer available, you are limited to building only as many links as you can pay the full cost for, including beer.

Source: Core Rulebook (pp. 12, 6, 8, 9)