FRUITING & HARVEST

Forced fruiting

Throughout winter and spring of the spawn run year you may see robust white mycelium growing on the ends of bolts, mycelium popping some wax plugs out of their holes, and a few incidental “volunteer” shiitake mushrooms fruit spontaneously on some bolts (Figure 1). These are all signs of a decent spawn run and that your bolts are readying for their first forced fruiting. Forced fruiting mimics a seasonal change which incites the shiitake fungus to produce fruiting bodies. Soaking provides a rapid influx of moisture mimicking fall/spring rain, and the temperature of the water is used to mimic the onset of cooler weather. Typically, bolts are soaked three times per year for forced fruiting, beginning at the end of May or beginning of June to try and incite a fruiting for harvest, with seven to eight weeks in between soakings. Larger shiitake production operations may have enough bolts to alternatively choose to force fruit a subset of bolts each week during the fruiting season to try and supply their markets more steadily. Forced fruiting does not always result in a reliable harvest from each bolt each time, but what it importantly does is that it puts harvest timing in your control, and concentrates shiitake yield potential into those times of the year.

Typically, a good number of your bolts inoculated with wide range strains should be ready for the first harvest attempt by the end of May or beginning of June in the PNW. Warm weather strains are less likely to be ready at this point, but there is a possibility that some may be ready as well by this time and may fruit depending on the specific strain and weather at that time of year. They are more likely to be ready to fruit by midsummer or late summer/early fall though. If you are able, you can soak your warm weather strains along with wide range strains being soaked for forced fruiting, because at the least, this should help hasten spawn run along even if they are not yet ready to fruit. At best you may get some mushrooms out of it.

Getting ready to force fruit:

Before a forced fruiting, soaking tanks and A-frame racks need to be all set up and ready to go. If you have already gone through the process of soaking bolts in the spawn run year, you likely already have:

• Water lines plumbed in

• ground decently leveled underneath the soaking tanks,

• any leaks found in the tanks sealed

• cross-boards cut (usually ~24” long and ≥ 1/2” thick) and a ratchet strap for each tank

Also,

• clear out any forest debris inside the tanks that may clog the drain ports,

• re-level your tanks if needed,

• make sure you have all of your drain plugs, or that your drain hoses are clear and have working on-off valves.

Having your A-frame racks ready to go means that:

• they are fully constructed,

• the 4’ x 10’ ground space underneath each rack is flat and clear of debris,

• you have enough 14’ x 16’ pieces of fabric (some of these will be your crib stack covers) and enough landscape fabric to construct fruiting tents for 10’ A-frame (see section below, and instructional video)

• any holes in your fabric have been repaired with waterproof duct tape.

Soaking for forced fruiting:

Bolts are put in the tanks before you fill them with water. This is because the bolts are very buoyant. Putting the bolts in before filling lets you arrange to fit as many bolts as possible into the tank, get the cross-boards situated, and ratchet strap tightened before the bolts start to float. The extra space on each rounded end of the stock tanks is advantageous for dealing with bolts that are not straight, have protrusions etc. You can often “puzzle-peice” them in by sliding awkward parts of the bolt into the ends of the tank so that they don’t take up excessive space in the straight section of tank that could otherwise be used to fit in more bolts. Allow just enough space between the top layer of bolts and the tank lips so that you can fit the cross-boards underneath. Often this will also keep all of parts of you bolts below the water line. You also want to have some pieces of wood handy to fill in any gaps between the cross-boards and top layer of bolts that might otherwise allow some parts of the bolts to float above the water line. The sides of the tanks will need to be supported with a ratchet strap or something similar to keep them from bowing outward once the tank is filled. Tighten the strap just enough to secure the cross boards completely under the lip of the tank and restrict any outward bowing of the tank’s sides. Bowing sides will allow the cross-boards to pop out. Trying to re-submerge the bolts after a board breaks loose is very difficult, and can damage the bark of the bolts.

Once all the above steps are complete, the tanks are ready to be filled with water. Ideally the water used is able to drop the temperature of the bolts by at least ~12°F. This is why it helps to have water that comes from an underground source, and why it helps to minimize any sun-heating of water lines going to the laying yard. If your main water line runs above ground for a significant length (especially if it receives any sun along that length), purge any warm water from the line before you start filling the tank. This may take several minutes if the line is several hundred feet long. If you want to be more precise, a simple kitchen thermometer can help you keep tabs on your water temperatures; from an underground source this . With a tank full of bolts, fill the tank right up to the brim, so that there is some buffer for any leaks that might arise, and for any water the bolts absorb. The bolts won’t absorb enough water to significantly drop the water level in the tank, but expect the level to lower slightly over the 24hr soaking period. If needed, top off the tanks before nightfall. A 2 x 2 x 6’ tank full of bolts will typically require about 92 gallons of water (equal to ~5.1 gallons per 5”-diameter bolt) to completely fill the tank; 100 bolts will require ~1,528 gallons of water per year to soak for three forced fruitings per year. To put this amount of water demand in perspective, 1” of irrigation water applied to 1 acre of cropland is equal to 27,154 gallons, so the water demand of these shiitake production systems is relatively low.

Setting up a fruiting tent around the A-frame rack:

After the bolts have soaked a full day (~24 hrs) they are ready to be pulled out of the tanks and put into an A-frame formation and into a fruiting tent. When timing a soaking, make sure your schedule will allow you to pull the bolts out at approximately the same time the following day, and that you have enough time thereafter to set up your bolts into the fruiting tent(s). The fruiting tent completely envelops all the bolts in a A-frame. It serves a dual purpose of protecting the mushrooms from drying conditions as they are fruiting, and also serves as an insect pest exclusion barrier. The fruiting tent is a modified version of “fruiting blankets” that are sometimes used in other regions for forest-cultivated shiitake. The difference is that the fruiting blanket is only laid overtop of bolts in the A-frame, while the fruiting tent completely envelops the bolts, adding important insect pest exclusion and improved moisture protection for the mushrooms. When the tent used as intended, the mushrooms produced will often be 95-100% marketable, provided they are harvested at the right time.

The fruiting tent fabric is laid out just before the bolts are removed from the tanks. A 14 x 16’ piece of fabric is ideal for a 10’ rack. This can be the same 14 x 16’ fabric piece used to cover two adjacent crib stacks over the summer. If the fabric has been outside, it should be folded up and soaked along with your bolts to purge any pests that may be on the fabric (Figure 2B) . The folding should be done in a way that makes it easy to unroll when it is heavy from being saturated with water, and prone to getting muddy while setting up the fruiting tent; watch Video 1 below for an example of how to fold the fabric, along with the rest of the tent setup. The fabric is laid out so that the 16’ dimension is oriented lengthwise under the 10’ A-frame rack. Often there will be a sewn seam running down the center of the fabric that can be used to help you line it up centrally it underneath the A-frame rack. Medium and large binder clips (the same as used for paper, sold by office supply retailers) are used for holding tent seams together and/or tethering it to the rack. The extra 3’ of fabric on either end of the 10’ A-frame rack is tethered with a binder clip ~3’ up on the rack’s posts so that the center 10’ of fabric is then centered under the rack. A barrier of landscape fabric (or something similar) is then laid on top if the tent fabric to protect the tent fabric from being damaged by the the bolt ends. Without this layer, shiitake mycelium will often grow into the tent fabric, and “fuse” the bolt to the fabric, making it hard to detach without tearing the fabric. At the least, a 1 x 10’ strip is needed on either side, or a single 4 x 10 strip can be used to cover the full base of the tent. All but the center 4’ of tent fabric on either side is then rolled inward to the edge of the landscape fabric. The tent fabric is always rolled inward like this to keep soil/mud from your shoes off of the tent sides and consequently off of the mushrooms.

Once the base of the tent laid out, immediately start pulling your bolts from the tank(s) and putting them into the A-frame formation. Timeliness in getting the bolts wrapped into the fruiting tent minimizes time for pests to get at the bolts. Be sure that fabric stays centralized under the rack as you put the bolts on it, and that the bolts ends aren’t getting placed on any inadvertent folds in the fabric. This will help you avoid a situation where it is hard to get the tent closed because of short and/or uneven fabric on either side. Position bolts so that there is enough space between then for the mushrooms to grow. Ideally each bolt should be touching other bolts as little as possible, but they should touch each other just enough to be supported by something besides the A-frame rack alone. If bolts have the opportunity to fall laterally, there’s a risk of a domino effect. Prioritize leaning larger, heavier logs against the cross boards if you can. Also alternate stacking bolts onto either side of the rack to keep one side from getting too heavy and pushing the rack over. If possible, is helpful to put bolts of different wood species, strain, and age into discrete fruiting tents, as these factors affect harvest timing; keeping them grouped like this will minimize the number of times you will need to completely open up the tent for harvest, and opportunities for pests to get in.

Once the rack is full of bolts, close the fruiting tent right away, and make sure the tent is completely “buttoned up”. Each seam along the ends and across the top can be made by evenly rolling them together and keeping the roll closed tight along the seam with with binder clips placed every few feet. There should be no gaps or holes in the fruiting tent. Pests will find them. Give attention to making sure that the tent fabric is wrapped around the rack posts reasonably well. Roll the fabric to make a seam in the direction opposite of the dominant wind direction to avoid wind from catching it and unfurling the rolled seam.

A good additional measure to take is to always make sure you have a canopy (or at least a tarp) ready to set up over your fruiting tents in case of rain occurring during fruiting. Although it may seem counter-intuitive, rain-wet mushrooms incur a significant loss of market quality. Tarps and/or canopies can also alternately be situated to protect against warm summer winds that cold lead to excessive mushroom drying (see Figure 4). A minor amount of drying is less likely to affect mushroom market quality as negatively as rain will, but it will decrease mushroom weight and excessive drying can lead to ceased mushroom growth (termed “abortion”, Figure 6A), therefore threatening profit potential. Canopies can be semi-permanently situated in your laying yard over your a frame racks for the longer-term to lower the seasonal labor demands of a temporary setup. Once the fruiting is season is over, the canopy tarp can be taken off the frame and stored inside until the next fruiting season.

Fruiting:

Fruiting responses will depend on strain, species of wood, age of the bolt, and whether the fungus has “rested” for long enough (i.e. consumed enough wood) to be ready to fruit for the first time or since its last fruiting. Shiitake also needs at least some light to fruit; the amount of sunlight under the forest canopy and fruiting tent fabric is more than ample. Wide range strains are more likely to fruit in late spring and fall, whereas warm weather strains are more likely to fruit from early to mid-summer into fall (also refer back to Table 1 on the Strains page). Research has illustrated that the strongest and most uniform fruiting responses are typically within the first year or two of production, then afterwards yield will begin to decline and become less uniform. This is because initially there is ample readily digestible woody matter for the fungus to consume, whereas later on in the bolt’s production lifespan, the this fraction of the woody matter becomes more scarce to the fungus. After the third to fifth year after production begins, growers may choose to take bolts out of production altogether if the fruiting response starts to become uneconomical. On an annual basis, one of the three fruitings from a given bolt may typically be larger than the other two, and sometimes the bolt may not fruit at all. This may especially occur after a bolt produces a particularly large fruiting (e.g. 2-4 average harvests-worth in one fruiting. The “hangover” that a bolt might get after producing a large fruiting may persist through several forced fruitings, until it has consumed enough wood again to be ready for another fruiting.

Provided the shiitake fungus is indeed ready to fruit and weather conditions are conducive for your strain(s), the cold water soak should incite “primordia” to form on the mycelial mat underneath the bark of your bolts. Primordia look like small bumps in the mycelial mat. On alder, birches, and hazels, the bark is thin enough to sometimes allow the primordia to be visible, resembling warts or boils, or ripples on the bark of the bolt. A few days after soaking, some primordia will continue to grow through the bark or out of the inoculation holes and begin to form immature mushrooms within a few days. This is commonly referred to as the “pinning” stage. See Figure 1A, 1B, and 1C on the Fruiting & Harvest Gallery page for visual examples of these stages of fruiting.

The length of time from when the soaking is finished until the mushrooms are harvest ripe also depends on the same factors influencing the fruiting response, along with the temperatures during the fruiting period. Most typically, the time from when soaking ends until the mushroom is harvest ripe falls within a range of 5-14 days. The temperature during fruiting will be the primary driver of how long this period lasts for a given strain. Many wide range strains typically have a relatively fast growth rate that may be as short as 5 days to harvest-ripe if daytime temperatures commonly reach into the upper 90s higher during fruiting. Warm weather strains will comparatively take longer to reach harvest ripe stage (~1-3 days later) compared to wide range strains growing in the same conditions. Younger bolts will often produce mushrooms that grow at a more uniform and vigorous rate (varying by only 1 day or so), whereas as the bolts age, the rate of mushroom growth will decline slightly and become increasingly more staggered, where mushrooms reach a harvest ripe stage multiple days apart. In trials, mushroom growth rates on sweet cherry bolts and birches have been observed to generally to lag behind mushroom growth on other wood species. This has been may be an effect of the difficulty that the mushrooms have in pushing through the bark of these species, as it is a trait that both species share.

Harvest:

Harvest is fairly straightforward. Examples of shiitake harvest and harvest-related information are also covered in Video 2. The mushrooms can be picked from the bolts as preferred; they can be twisted off at the base (traditional), or for further ease (and to avoid ripping off sections of bark along with the mushrooms) cut off at the base with a knife or shears. In addition to gentle and-food safe handling of the mushrooms, the most important part of successful harvest is developing an understanding harvest ripeness. In traditional Asian markets such as those in Japan, there are commonly multiple market classes that correspond with different stages of harvest ripeness, thickness of the mushroom cap, aesthetic appearance, mushroom moisture content, and times of the year in which the mushrooms are produced. Most domestic shiitake markets tend to be far less discerning (especially if selling direct-to-consumer), but certain markets may still be. Besides delivering clean, pest free mushrooms, timely harvest is the main aspect of mushroom quality control management that is under your control. Mushroom moisture content is generally hard to manage in forest cultivated production systems, but critical degrees of moisture content flux can at least be moderated via your fruiting tents, and protection provided by rain canopies, and/or wind screens (Figure 4).

It’s generally advisable to refrain from opening the fruiting tents frequently to check on mushroom growth; this will minimize chances of pests getting inside, as they often will be lurking within the folds of the tent seams. Checking on your fruiting mushrooms four to five days after soaking is a reasonably conservative timing to make sure you aren’t opening the fruiting tents excessively, but still won’t miss an optimal harvest timing. If the weather has been very hot throughout fruiting, some wide range strains may be ready to harvest after five days. In this type of hot weather, the harvest-ripe window may also be no more than one day, especially with wide range strains. Otherwise, during most of the PNW shiitake growing season (early June-Early October), the majority of wide range strain mushrooms will be ripe 6-9 days after fruiting, with a peak harvest-ripe window of 1-3 days. These estimates may be several days later for warm weather strains. If you need to harvest with very close attendance to harvest ripeness because your market is very discerning, your harvest may need to entail doing a cutting each day over a ~3-5 day period. Otherwise for a less discerning market, two to three cuttings over the same 3-5 day period of time may suffice for capturing most mushrooms at varying degrees of harvest ripeness.

Identifying harvest ripeness:

The beginning of harvest ripeness is determined by whether the veil on the underside of the mushroom cap has begun opening to show the mushroom’s gills; this early end of the mushroom ripening spectrum is the the “waxing” stage (Figure 5A). When the the underside of the cap opens enough to show the majority of the gills, but the edges of the cap are still facing down and inward, this is “full” harvest ripeness. Full ripeness is when the mushrooms are around the peak size/weight that they can attain while still retaining desireable market quality characteristics. Generally, mushrooms on the waxing end of the fully ripe stage are considered to have the most desireable market quality (Figure 5B). Fully-ripe mushrooms with caps that have begun to flatten and thin are considered to be slightly lower quality, even if the cap edge is still curled down and inward (Figure 5C). Mushrooms allowed to grow further to a stage where the cap edge begins to turn down and outward may grow slightly larger than those at full stage (Figure 5D), but any weight gains are countered by a progressive decline in market quality as the mushroom moves deeper into this “waning” stage. Mushrooms allowed to wane further to the point where the caps have begun to turn upward and/or have begun dropping white spores (sporulation), are considered to have waned completely and are no longer marketable (Figure 6B). Sporulation is particularly damaging to market quality, as any mushroom caps below a sporulating mushroom can be covered in spores. The spores will then be wetted with moisture on the mushroom’s cap to form a thin, unappetizing layer of clear to grayish-colored slime (Figure 6A). Sporulation is likely to occur quicker when mushrooms are growing in temperatures nearer to the upper threshold of their fruiting temperature range. A short video of shiitake mushrooms sporulating can be seen on the Glossary page. Alternatively, when strains are fruiting at lower end of their fruiting temperature range, the mushrooms will usually show more apparent resistance to waning and sporulation. Some markets may even value mushrooms that are still slightly underripe, and be willing to pay a premium price for them.

Often the majority of fruiting mushrooms of the same strain, growing on bolts of the same age and wood species, will reach harvest ripeness on the same day, although some variability across any given bolt should be expected. Very generally, a mushroom’s potential to size up will correlate with the size of the stem; e.g., thin stems = limited growth potential and vice versa (Figure 5B). Sometimes the caps of mushrooms of certain strains and those growing on younger bolts at the lower end of their fruiting temperature range will get relatively large before the veil begins to open. In some more traditional shiitake markets, mushrooms with caps that have grown to a reasonable size but still retain a closed veil are considered to be premium quality. The premium is justified by the fact that the mushroom could have otherwise been harvested at a slightly later and sold with a higher market weight. The parameters of what constitutes “quality” shiitake will be relative to the demands of your specific market, but in general, shiitake that have been damaged by insects, have been overly desiccated by wind (Figure 6A), have been overly-exposed to rain, have become over-ripe (Figure 6B), or have had spores deposited on them (Figure 6C) are commonly considered to be non-marketable. Of these, rain-wet shiitake may be the most redeemable because they may still be harvested at a good harvest-ripe stage, but their post-harvest lifespan and their culinary application will be limited. For other examples of variability in mushroom fruiting (and potential causes) that might be encountered, see the Fruiting & Harvest Gallery page.

Harvest food safety fundamentals:

Although shiitake mushrooms should always be cooked, killing pathogens in the process (therefore they are type of produce with a “kill step”), taking simple measures during harvest to avert any potential food safety issues or grey areas regarding shiitake mushroom exemption from produce safety regulations is advisable. Harvesters should adhere to good hand hygiene and avoid harvesting while ill with communicable bacterial or viral infections. Use of disposable gloves (and/or masks) during harvest can also be considered. Harvest mushrooms with clean implements and harvest into clean harvest receptacles to avoid cross contamination with human pathogens. Avoid having any sides of your harvest receptacles that are touching the mushrooms also come into contact with the ground/soil, or anything else that could get mushrooms in contact with a fecal-oral contamination pathway (for example: restroom floors > shoe bottoms > ground > mushroom dropped on the ground where people are walking during harvest). Also because inner side of the fruiting tent material touches the mushrooms, the sides of the fruiting tents should be rolled or folded inward for harvest, to avoid walking on the side of the fabric that will again potentially touch mushrooms when the tent sides are put back up between cuttings on different days. A common food safety faux pas to be aware of regarding forest-cultivated shiitake is avoiding the impulse to blow off (with one’s breath) any bark or moss that may be on the harvested mushrooms. These residues can alternatively be gently brushed off with a clean (or gloved) hand, or with compressed air later on, post-harvest if they are not tolerated by your market.