Some say the grass grows toward water while others will tell you it grows toward the setting sun. Given that there is water everywhere on the golf courses and that most greens are not very flat, look for the grain to generally flow downhill. 

To determine the grain for yourself, take a look at the different shades of green you see on the putting surfaces. If you see light or shiny grass, you are looking down grain and the putt will be faster. Darker grass means you’re looking into the grain and the putt will be slower. Often you’ll see a putt where the first half might be light and the second half dark. (See Photo) This means it will be fast at first and then slower as it starts going into the grain. If you walk around to the other side of the hole you’ll see the colors will have reversed and what was once light has become dark. Now you know why sometimes when you think you’ve hit the ball hard and it comes up short and other times you may feel you “just tapped it” but the ball screams past the hole.

You can also look at the rim of the cup and will likely notice a “ragged edge” on the down grain side of the cup. It may appear to be brown and a little scorched. That means the grass is growing away from the cup unlike the other side where the grass may very well be growing over the edge into the cup.

Some players like to add a little loft to their putter by tilting the handle slightly to the right of the ball when they’re putting into the grain. This can get the ball more “on top of the grass” in hopes to dampen the effect the grain may have on the roll of the ball.

Needless to say, grain isn’t the only factor to consider when reading a putt but it can certainly make a difference, especially onBermudagreens. 

Here the ball is resting on the ragged edge of the cup

One can easily see the various shadeds of green that the grain produces

http://www.icontact-archive.com/ujqQxFvfuc4RnCzhkN8IDGYK1PBwp7WB?w=2.

Golf Ball Hitting Steel At 150mph – Slow Motion (70,000 fps).