"Barley grass" is just barley harvested for the tender young growth instead of letting it mature to grains. I haven't grown barley grass for juicing, but I have grown and started a lot of plants in pots using the technique below with excellent results.
Since you want to grow indoors, start with a sturdy tray at least 3" deep. Make sure the tray has drainage holes so there will be no standing water.
Get your seeds -- you'll have to decide what variety to use based on whatever you're trying to achieve. I would look for varieties specifically promoted for use in growing barley grass; some barley cultivars have specific cultural requirements that would seem to make them poor choices for your application.
Create a soil mixture using:
- .5 gallon peat
- 1/4 cup pulverized lime
- .5 gallon perlite or vermiculite
- .5 gallon finely sieved high-quality compost (1/4" mesh sieve)
Reserve a small amount of the perlite to use for top dressing after planting.
(Adjust the quantities if you need more or less, but maintain the ratio.)
Add this mix to your pot to a depth of 2". Water thoroughly -- slowly pour water evenly over the entire surface until water comes out the drain holes in your tray. Wait a while (maybe an hour or two) and then repeat this process. You want the potting mixture to be thoroughly wet.
(See note regarding chitting at the bottom of this post.)
Broadcast your seed across the surface of the soil. As you saw in the video, it should be planted rather thickly, but you don't want it so thick that there's a layer of seeds on the surface -- the plants need a little bit of space to breathe. Your experimentation and experience will be the best teacher here. (Or see the reference at the bottom of this post.)
Sprinkle the top with about 1/4" of the reserved perlite.
Set the tray in a cool, dark place.
Some people would tell you to cover the tray with plastic wrap at this point -- I don't like to do this because it creates the potential for problems with mold/fungus. It does have the advantage of holding moisture in, which the germinating seeds need.
During germination keep the soil moist -- mist lightly with water 1-2x daily. Don't let it dry out during germination! You should see sprouts within 1-3 days.
As soon as you see sprouts, move the tray to the light. Most of the time "a sunny window" is not sufficient. I would use fluorescent lights -- position the lamp 1" above the surface of the soil, and raise the light as the plants grow so that they stay 1-2" from the lamp. If you have a sheltered spot outside that gets all day sunlight, you can grow outside. (This will dry out the soil faster, adjust your watering accordingly.) It's harder to get sunshine all day indoors, but if you think you can provide it, give it a try.
Do not over water, but don't let the soil get dried out either. How often you will need to water depends somewhat on the environment you provide. (See notes above regarding outdoor sunshine vs indoors vs lights.)
Within a couple of weeks it should be ready to harvest at 6" or higher. You may be able to get a couple of cuttings if you maintain the light and water.
As I got to the end of writing/researching this post, I stumbled across this reference on growing barley grass, which confirms for the most part the advice I've given above. They have different recommendations regarding growing medium -- try both approaches and see which works better for you. They also have recommendations for amount of seed to use in terms of density. And they claim chitting (pre-sprouting) is required, but I'm skeptical about the need -- try it both ways to see whether one way is more work or provides more yield.
I'd recommend taking a look around their website -- especially this note on barley grass:
Many folks have been seduced by advertising, into thinking that Barley is the way to go. As we say - research we've seen does not indicate that - and frankly, the juice of Barley Grass is horrid! We will mix Barley with Wheat (4:1 wheat) as they grow at the same rate, but we have found no other way we can even tolerate Barley Grass juice.
In doing research for this post, I'd have to agree with their skepticism on the outcome you can expect from barley grass juice. The research does not seem to have confirmed much in terms of benefits.