What: Shares of craft beer maker Boston Beer Co Inc (SAM -1.97%) fell 11% in January according to S&P Capital IQ data, a move driven by an analyst downgrade.

So what: On January 8, Jeffries analyst Kevin Grundy downgraded the stock to a hold rating with a $210 price target. Between the stock's close on January 7 and the end of trading two days later, the stock had fallen 11%. The analyst pointed to increased competition from the liquor business and a further consolidation in the beer business. 

Now what: The danger with Boston Beer company has always been its high earnings multiple. Shares trade at 22 times forward earnings now, higher than the ratio of 16 for the S&P 500, and if the company can't continue to grow investors won't keep the multiple that high.

The drop in January due to an analyst downgrade may not be worth worrying about long-term, but investors should be watching for slowing growth and increasing competition. Boston Beer has ridden the growth of craft beer for a long time, and it may be entering a more mature phase as most major brewers do.