Recent episodes

The Science of Making Great Beer How do yeast, water, hops and grain combine to form a lager, pilsener or ale? The process requires careful supervision and tightly controlled conditions. Expert brewmasters explain how temperature, timing and ingredients all factor into making an excellent beer.

Communities Take Action to Protect Great Lakes The five Great Lakes — Ontario, Erie, Huron, Michigan and Superior — are said to hold one-fifth of the world's surface fresh water. The lakes are threatened by fluctuating water levels, invasive species and pollution — and nearby communities are looking for ways to help.

Scientists Mark 25 Years of HIV Research In May 1983, the first scientific papers were published describing the possible connection between a retrovirus and the development of AIDS. The virus went on to become known as HIV. Experts discuss whether, 25 years later, scientists any closer to a cure for AIDS or to a vaccine to prevent HIV transmission.

Study: Sahara Gradually Dried Up Over 6,000 Years What made the Sahara Desert go dry — and are there ancient waters still hidden below the sands? In a controversial study published in the journal Science researchers argue that the drying of the Sahara took place over thousands of years — not suddenly as was previously thought.