Fed Balance Sheet Chart ...there ...THEREisT...HERE THERE IS  good reason to worry about the ability of the Federal Reserve to prevent the massive build up of the monetary base from resulting in out of control inflation.

One of the sources of the growth of the monetary base has been the 
$1 trillion of purchases of mortgage backed securities by the Fed. Much of that hasn’t yet made its way into the broader economy, and instead sits on bank balance sheets. Actually, much of it is on deposit with the Fed itself, where banks can earn risk-free interest instead of lending it to home buyers at risk of losing their jobs or businesses still suffering from diminished consumer demand.

When the economy begins to recover, the Fed will need to reduce the monetary base to prevent all those dollars from flooding the market and triggering hyper-inflation. For some sources of monetary expansion this is relatively straight forward—the Fed can simply shut down various monetary easing facilities that operate like loans to banks. Banks will have to hand 
dollars over in exchange for the collateral they posted to participate in the lending facilities.

But things are not as easy when it comes to the mortgage backed securities the Fed purchased this year. These purchases increased the monetary base, which means they will have an inflationary effect when bank lending loosens. In order for the Fed to start sucking back these funds, it will have to sell these into the market. Unlike the repo and lending programs, however, the Fed cannot simply order the banks to repurchase the mortgage backed securities. It will have to sell them at market prices.

The market’s knowledge that the Fed has become a seller rather than a buyer for mortgage backed securities will likely result in the pricing of these securities falling. In order to bring the yield of these securities up to a level acceptable to the market, they will have to be sold at a discount. This discounting means that the Fed will not be able to withdraw as much liquidity as it added, leaving some portion of that $1 trillion (plus its multiplier effect) in the economy to create inflation.