Pulse brewing and what it means in the cup.
Brewed coffee equals hot water + coffee grinds + time for the two to mix.
And there is the rub—that combined time is called “contact” time, and if it is too short, the water will not fully “extract” the acids and other compounds that make up fresh brewed coffee. And if the contact time is too long the result is over-extraction—the pulling of too much of the bitter elements that lead to a marriage gone bad. Too weak in the one case, too harsh in the other.
One way to optimize contact time is through the technology of “pulse brewing”. Here is what that means: a portion of the total hot water that is going to be delivered into the brew basket is allowed to drip into the basket, over and into the grinds, and then the flow is stopped. The grinds that are receiving the water are said to be pre-infused. They absorb the incoming water more effectively than do dry grinds, just as a dampened sponge blots a spill more effectively than does a dry sponge.
After a 10 or fifteen second time-out, during which the grounds continue to “set-up,” more hot water is delivered into the brew basket. The pre-infused grinds are prepared to give up the flavor compounds and acids that make up the character of the coffee.
This cycle might be repeated several times. The resulting brew time may be extended by a minute or more. The grinds and water interact for the maximum extraction while avoiding drawing out undesirable acids which ruin the brewed result. It is a balancing act.
Some brewers have a less efficient, small spray head that does not deliver enough water within the optimum time to begin with. This is a good place to have a pulse brewing option. Or maybe you want to brew a particularly heavy load of grinds, for stronger coffee without the dark roast profile. Pulse brewing will allow the incoming water enough time to pass through the grinds without overflowing the basket.
Just as pulse brewing is good for heavy loads, it is useful also for very light loads, where there are not enough grinds to carry off a strong enough brew. Pulsing can be used to pull the last molecule of flavor from the light load. This is not recommended for good coffee, however, as it is perhaps a stretch too far.
Outside of these extremes, pulse brewing may be a complication without benefit. One of the great strengths of the Bloomfield spray disk design is that it is a large (several inches) plate with twice as many drain holes for the outgoing water to pass through compared to the conventional “spray head.” The result is gentle streaming, allowing saturation of the grounds and the correct agitation between the water and the grinds. Perfect coffee is the reward without fussy programming and menu set ups.
And of course, if you do need pulse brewing, well, we have that too.