How to choose a mate?
I suggest buying a traditional mate made of gourd. It mellows with age and absorbs the taste of yerba. The only advantage of a metal mate is that it is easier to pack while traveling. I personally prefer the gourd.
A new gourd must be properly prepared. First, you put yerba inside, then you pour hot water into the mate and leave it for one day. Next day you throw out all the contents, wash the mate and scrape the remains of the fibers of the gourd walls. You may repeat the whole process once again: put yerba inside the mate, pour boiling water and leave it for another day.
When you become addicted to this energizing beverage, you should think about buying a thermos. In South America there are special thermoses for drinking mate. They are equipped with a pipe that facilitates pouring water into the mate. Nevertheless an ordinary thermos is good as well. A thermos is especially handy while being outside, and people carrying thermoses on the streets are nothing strange in Buenos Aires or Montevideo.
How to prepare a mate?
Warm up water. It is important to remember not to boil it. The temperature of water for mate should be around 70°C. Lazy sipping of mate is so natural in the north of Argentina, that in the streets you may find machines with free hot water. An important element of such machine is a thermometer showing the temperature of water. Too hot water burns the leaves and makes mate watery and tasteless. According to some sources it is not only due to excesive temperature but also to the amount of oxygen dissolved in water, which is much lower in higher temperature.
Fill 3/4 of the mate with yerba. Tap the opening with your hand and turn the mate upside down, shaking lightly. Turn it back to its normal position, inclining slightly so that most of the leaves gather on one side of the gourd. Thrust bombilla into the side where there is less yerba. From that moment on don't move the bombilla. Next pour hot water inside. Do it slowly. You may pour it over the bombilla. Water should cover all the leaves. Wait a moment until the infusion get stronger. At last, drink!
Some people prefer to drink sweet mate. In such case you put some sugar into the mate before each pouring of water into it. You must however remember that a gourd used for drinking bitter mate should never be used for drinking a sweet one.
Yerba mate may also be drunk with cold water with addition of ice and some refreshing herbs. Such beverage is called tereré and is popular in Paraguay.
How to drink?
Drinking mate is not only a way to quench. It is a ceremony. A comparison to smoking a peace pipe will not be exaggerated. You often drink mate with a bunch of friends and invitation to the ceremony may be a form of social acceptance.
A host usually plays the role of a master of ceremony. It is him who prepares mate, pours water in and customary drinks first. He drinks until the mate is empty and the air starts to enter the bombilla. Nota bene the sound of slurping is very acceptable here. Next he pours new water in and gives the mate to first of his guests. According to the rules of Southamerican savoir-vivre, the bombilla should always point at the person to which mate is offered. The guest drinks until he empties the mate, which is signaled by slurping, and gives the vessel back to the host without saying “thank you”. If you thank your host he understands that you don't want more and will pass you over during the next round. All the guests get their mate, one after another. Then it is host's turn again, and then the second round starts in the same order.
When the mate starts loosing its taste, the host throws out all the contents (using bombilla) and fills it anew. The ceremony lasts as long as the last of the guests wants to drink. However drinking mate is not the focal point of the meeting. It is only a pleasant addition accompanying the meeting.
From time to time the bombilla gets clogged. Then some people rub the bottom of the mate with palm of their hand and the bombilla gets unblocked. I don't know how to explain this phenomenon, but it works.
Generally there is some magic involved in mate. The Argentineans say that you need a good hand for mate. And in fact there are some people, who will never prepare good mate!