|Basic recipe for preserving all types of truffles|
1 part truffle, coarsely chopped
3 parts fresh lightly salted butter
Drain all free juice from the truffles (hard truffles will not tend to "weep", though any soft truffles will); reserve juice and either salt the juice lightly to preserve or use immediately. Whip butter and truffles together by hand or in a food processor; pack tightly into a sealed jar. Do not can with heat. Make sure the top layer is entirely butter; do not allow any truffle pieces to be exposed on the surface. This product will keep in the refrigerator for up to one year in my experience, or indefinitely in the freezer, though some quality is gradually lost over time. If mold grows on the surface, scrape all traces of mold, discard mold and freeze the product.
Oil crocking recipe
Whole or cut Italian white truffles or unpeeled Perigord black truffles, brushed absolutely clean and dry
Enough light, mild flavored oil to completely cover truffles, at least 5× volume of oil per volume of truffle in jar.
For Italian whites, use a mushroom brush, a pastry brush or soft cloth to carefully remove all dust and dirt from the surface without using any water. Cut large Italian whites into chunks no bigger than 3/4" across for best preservation. For Perigord or Chinese (hard shelled) black truffles, scrub them with a toothbrush dipped in brandy, then dry them thoroughly. Cover completely with oil (surface should be at least 2" above truffles) and shake gently to eliminate air bubbles and to be sure the truffle pieces are completely covered. Seal the jar (do not use heat, but you might use plastic wrap or nitrogen gas to eliminate oxygen contact with surface), and refrigerate. Cut truffles will keep longer in butter or oil, but will not retain as much flavor. If you wish to preserve the truffle products for the long term and allow most of its flavor to leach into the preserving agent, chop the truffle very finely and cover it completely with enough oil to stand at least several inches over the cut truffles.
Preserving hard-shelled truffles (French, Chinese and Italian black)
Peeled or unpeeled black truffles (methods will differ) Butter, oil or pure good quality brandy, preferably alambic, 4–× volume per 1× of truffle To preserve whole black (hard shelled) truffles, scrub clean with a toothbrush dipped in brandy and dry thoroughly. Cover completely with butter or oil, and refrigerate or freeze. They may also be peeled, chopped coarsely and mixed with butter, and the resulting product will last longer under refrigeration. Another preservation method that can be used to greatest effect and economy with the peels alone, though it can also be used on the whole or halved product, is to cover completely with a good quality brandy, preferably alambic or armagnac, and refrigerate in a sealed jar. The intensely flavored brandy can be used in sauces or sprinkled as is on a dish for flavoring. It should be cooked only long enough to eliminate the alcohol (if that is desired) or flamed, though the peels themselves can be simmered into a sauce for up to an hour. Some early French chefs also cleaned and preserved black truffles in port wine or vinegar, but I believe brandy gives a better and more consistent result for preservation, though both port wine and good wine vinegar are very fine matches for the black truffle when it is simmered in a sauce.
Notes on preservation
These notes are the result of one year's worth of truffle preservation experiments; the recipes and techniques that survived the year are listed here along with the spectacular failures. Note that all of these methods also require supplemental refrigeration; room temperature is not good for truffles in any way, shape or form.
The following methods were tested: freezing in oil, freezing in alambic brandy and oil, crocking in cognac and oil, crocking in oil alone, storing in brandy alone, laying down in moisture-controlled sealed jars of rice or polenta, rubbing lightly with oil and/or alambic brandy and storing in rice.
Freezing truffles completely covered with oil—butter, duck fat or reserved foie gras drippings seem to serve best to fully coat and preserve the mushrooms—has yielded excellent results for Oregon truffles, Perigord and Chinese black truffles, with good product quality being maintained for up to a year. Frozen truffles are best cooked. Be sure that no truffle surface is left exposed; the mushrooms must be completely covered in fat to avoid freezer burn. And don't thaw the product before adding it to a dish; I found that frozen soft truffles turn into flavorless mush within an hour of defrosting, and the hard ones tend to dry up. Use them before you lose them.
Freezing truffles without oil is one of the spectacular failures. The product ends up dry and tasteless within days. Likewise, canning removes the majority of the flavor. I have found, in five years of searching, buying and experimenting, only one canned truffle product which I felt retained anything close to the genuine truffle aroma, a Tartuffon white truffle creme from a company in Italy. Urbani also makes an excellent white truffle cream product in a tube.
Refrigerating in brandy yields very respectable results with the hard-shelled black truffles, and poor results with most other types. Mixing a few drops of brandy in with the preserving oil before freezing again yields good results with hard shelled truffles and odd results with soft truffles. Truffled brandy is delicious to add savor to sauces or meats when added at the last minute.
Crocking in pure, unflavored oil such as grapeseed or a very light olive oil gives good results for the Italian white truffle as well as the hard shelled black truffles, and mediocre results for the Oregon soft truffles. The truffles infuse the oil with much of their aroma and taste, but I have noticed an interesting phenomenon: the oil can and does get supersaturated with the truffle aroma if you use enough truffles, at which point the truffles seem to stay much fresher and retain more of their properties. I know of no other preservation method that works well for the delicate Italian white.
Laying truffles down in a covered bed of rice or cornmeal yields good results for short term storage in the refrigerator, and also produce a delicious by-product of flavored rice or meal for risotto or polenta. This is a short term method and will not keep truffles for longer than two weeks at the maximum in reasonably good culinary condition. Some extension on this period can be achieved by scrubbing hard shelled truffles with brandy, and lightly oiling, as this inhibits mold spore growth on the outside of these truffles. This method yields mixed and uncertain results with Oregon soft truffles, and very poor results with Italian white truffles.
Cleaning and preparation
To clean and prepare truffles for storage, use a soft basting brush or mushroom brush. Carefully clean any mold and dirt off of them. Do not wash soft truffles such as the Italian white or any American soft truffles. For sturdier truffles (the hard-shelled black truffles, the Perigord and Chinese), use a clean toothbrush dipped lightly in a good quality brandy (alambic works best), then dry.
If you find serious mold on a hard shelled truffle's surface, it may still be salvageable. You can (as a last resort) scrub thoroughly under running water, or with a hard bristled "truffle toothbrush" dipped in alambic brandy. If you can successfully scrub off the mold and it has not penetrated the shell, and the aroma is still good, this truffle may still be preserved either by freezing in oil or butter or for a day or so by giving it a final scrub with the toothbrush dipped in oil and burying it in cornmeal or rice in a refrigerated container. If you are unsure, slice the truffle in half and look for soft or moldy bits, and smell again for off odors. Be sure to thoroughly dry off all truffles before attempting preservation.
Partially rotted truffles are best preserved by slicing off the rotted parts, chopping the remainder coarsely and whirling it into about 3× the volume of pure, lightly salted butter, then freezing the resulting truffle butter.