I’m getting ready to brew my first pseudo-lambic. I opened two ounces of 1.9% AA Styrian Goldings pellets and stored them in a 100 °F (38 °C) greenhouse for the last two months so that they got good and stale. If the only reason we’re adding these hops is for the antimicrobial behavior, how long is enough and how long is too long? In fact, is there any reason to boil the wort past the hot break?
I don’t think there is a real science to producing old hops for the use in lambics. Your hops sound like they have been thoroughly abused and are probably in good shape for your intended use. If they don’t smell like fresh hops, don’t have the nice oil rub of fresh hops and are a tanner shade of brown, then your hops are probably not fresh hops. The hops are probably the least of the challenges most homebrewers face when they decide to embark on the pseudo-lambic voyage.
For the sake of this answer I will assume that you intend on purchasing a liquid yeast and bacteria blend from a yeast lab. Wyeast and White Labs both sell lambic cultures. The idea here is to inoculate sterile wort with a specially blended culture. This principle is no different than when you brew a “normal” beer and inoculate the wort with a single yeast strain.
Lambics, truly among the funkiest cats in the beer world, are not the products of total neglect. While the methods used to brew lambics in Belgium are (to say the least) odd when compared to brewing an über clean helles, one must remember that the native organisms required for lambic production are indigenous to the specific locale around this small grouping of breweries. Exposing un-pitched wort to other environments will probably result in a much different beer. And if I were a gambling man would wager that the end result would probably not be at all enjoyable. This means that when you boil your wort you also want to kill the usual suspects, mainly Lactobacilli.
The next challenge when brewing these types of beers is to simply leave them alone. Articles published about lambics often have graphs showing how microbial populations wax and wane during the course of lambic maturation. As populations come and go they leave behind key flavor components and set the stage for other populations to take over, often times the next population gets nutrients required for growth from the dead cells of the previous dominant organism. After considerable time the beer will become sour from the growth of certain bacteria. In addition to sourness, lambics have a complex aroma that is largely due to the growth of Brettanomyces species. Brett is known for its contribution of a variety of aromas including 4-ethyl phenol (classic phenolic aromas, such as medicinal), 4-ethyl guaiacol (smoked bacon, spicy, clove) and isovaleric acid (sweat, dirty sock, cheesy). Brett is also known to contribute aromas such as wet dog, creosote, plastic, horse-blanket and vinegar. Mmmmm — wet dog!
My advice is to keep in mind that what makes a lambic is the fermentation and aging process. You should aim to produce clean wort with the ingredients you have chosen, including your old hops, and exercise patience while your lambic culture goes through the various phases of this interesting process. Sampling is of course required, but I would wait at least 9 months if not longer to take the first sample. Continuous sampling does not speed things along and with these types of beers it is often best to stick them in the corner and forget them for a while.