Read this and answer the question. If the question is unanswerable, say "unanswerable".

A microbrewery, or craft brewery, produces a limited amount of beer. The maximum amount of beer a brewery can produce and still be classed as a microbrewery varies by region and by authority, though is usually around 15,000 barrels (1.8 megalitres, 396 thousand imperial gallons or 475 thousand US gallons) a year. A brewpub is a type of microbrewery that incorporates a pub or other eating establishment. The highest density of breweries in the world, most of them microbreweries, exists in the German Region of Franconia, especially in the district of Upper Franconia, which has about 200 breweries. The Benedictine Weihenstephan Brewery in Bavaria, Germany, can trace its roots to the year 768, as a document from that year refers to a hop garden in the area paying a tithe to the monastery. The brewery was licensed by the City of Freising in 1040, and therefore is the oldest working brewery in the world.

How often can a microbrewery produce 396 thousand US gallons?
unanswerable