When it comes to selling mushrooms, two of the recurrent questions of new customers at the farmers market are “How do I store them?” and “How long can they be stored?” Many farmers will answer with “You can store them in your fridge inside a paper bag for up to 5 days,” and that’s fine as a rule of thumb but you may be leaving money on the table.
What do I mean by that?
The shelf life is, in the end, the main parameter of the overall quality of your mushrooms.
Why is that?
It’s because the actual shelf life is determined by the change in color and weight loss of the mushroom itself. The faster these two changes are happening, the shorter the shelf life. The change in a color called browning is caused by spontaneous oxidation, and the activation of an enzyme called tyrosinase.
Other causes are bacterial blotch and or yeast. As well as bruising.
Weight loss is impacted by the storage temperature as well as the atmosphere (O2/CO2 ratio). Both temperature and atmosphere will affect the respiration and transpiration rate of the mushroom.
With this in mind, I realized more and more that the shelf life of mushrooms depends not only on how you store them. It already starts with the strain selection.
With that said let’s dive into the 8 aspects and best practices that will impact the shelf life of your mushroom.
Overview of the 8 aspects
Mushroom strain selection
If you keep the change in color and the weight loss of your mushroom in mind, then the earliest impact of the shelf life starts with the strain selection. This is because all strains behave differently during the cultivation stages and especially during storage.
Because of these behaviors, researchers are breeding new strains in order to increase shelf life. In such an attempt, the researchers crossed two strains to create a new hybrid which showed an improvement of the shelf lifetime (Figure 1).
In Figure 1, we can see four different strains that were stored at 4°C for 40 days. While the control and the two parental strains are showing browning, the new hybrid seems to be not affected at all.
Figure 1: Fruiting body after storage at 4°C for 40 day. A: Control, B: Parental strain 1, C: parental strain 2, D: new hybrid strain[1]
This behavior can be shown by measuring the L values and b values of the mushrooms (Figure 2). While at the starting day all four mushrooms have similar L values (Fig. 2 A, black) and b value (Fig. 2 B, black) these values are changing after 40 days at 4°C (Fig. 2, grey).
While the L value is an indicator for the whiteness of the mushroom the b values reflect the yellowness of the mushroom. In this sense, a high L value and a low b value are meaning a whiter mushroom.
The L value of the new hybrid is after 40 days (55-60) higher than the L values of its parental strains (40) and even higher than that of the control strain (50-55). While the b value of the new hybrid is lower (17) after this period while the others are above 22.
Figure 2: Changes in (A) Hunter L values and (B) Hunter b value of the pileus of the fruiting bodies after storage at 4°C for 0 and 60d[2].
Besides these two values (L and b) the weight loss during storage is as mentioned as another factor. The impact of different strains on the amount of weight loss can be seen in Figure 3.
Figure 3: Weight loss of different Agaricus bisporus strains stored at 2°C
In my article 26 Delicious Mushroom Species You Should Cultivate I give you an overview of a variety of mushrooms of what other mushroom farmers are growing and selling.
Additives to the irrigation water
To reduce the bacterial blotch and yeast population, respectively keep them in check, several studies focused already on the fruiting phase. It could be shown that adding of 0.3% CaCl2 (Dow Flake, Process R Grade) to all water applied to the casing layer after pinset through the end of the crop resulted in a better mushroom quality (Figure 4 and Figure 5).
Figure 4: Influence of 0.3% calcium chloride added to irrigation water on (A) yield and (B) initial color (L value) of off-white hybrid mushrooms[3]
Figure 5: Influence of 0.3% calcium chloride added to irrigation water on postharvest browning of mushrooms stored at 13°C in PVC-overwrapped packages[4].
A different approach was used by Chikthimmah in 2005. In his article, he compared 0.3% CaCl2 with a solution of 0.3% CaCl2+ 0.75% H2O2, and a solution of 0.75% H2O2 alone added to the irrigation water (Figure 6 to 9) and showed that adding them could reduce both the bacterial population (Figure 6) and yeast population (Figure 7).
Figure 6: Aerobic bacterial populations in fresh mushrooms grown using alternate irrigation treatments and followed by postharvest storage in overwrapped Styrofoam tills for 6 d at refrigeration (4°C/39.2°F) or abuse temperature (12°C/53.6°F)[5].
Figure 7: Yeast populations on fresh mushrooms irrigated with various antimicrobial irrigation treatments and followed by postharvest storage in overwrapped Styrofoam tills for 6 d at refrigeration (4°C/39.2°F) or abuse temperature (12°C/53.6°F)[6].
In Figure 8, we can clearly see the impact of the different irrigation treatments with 0.75% H2O2 or 0.3% CaCl2+ 0.75% H2O2 delivering the best results.
Figure 8: Photograph of postharvest mushrooms (12 d of storage at 4°C) from initial blotch-free crop irrigated with alternate irrigation treatments[7].
The impact of the storage temperature can be seen in Figure 9. Here the storage at 4°C delivers a way better results than stored at 12°C. Within in one temperature regime, the treatment with 0.3% CaCl2+ 0.75% H2O2 again improved the outcome quite a lot. Especially if we keep in mind that for this test, the author used a crop with mild blotch symptoms.
Figure 9: Photograph of postharvest mushrooms (6 d of storage at 4°C or 12°C) from a crop with mild blotch symptoms irrigated with tap water (top) or 0.3% CaCl2+ 0.75% H2O2 (bottom). [8]
Harvest timing
The third factor which will impact the shelf life of your mushrooms is the day of the harvesting. This effect is shown in Figure 10 (A). Here a higher maturity index indicates a late harvest. While the development of the cap seems to be affected by the timing of the harvest, the color ΔE is showing an inconsistent effect.
Figure 10: Influence of maturity at harvest on postharvest shelf life as indicated by (A) cap development (increase in maturity index) and (B) browning rate (increase in DE) in storage at 13°C. Means followed by the same letter on the same day are not significantly different at p=0.05[9].
Nonetheless, these results indicate that harvesting mushrooms at an earlier stage of maturity can improve the quality of the mushrooms and thus the shelf life without sacrificing yield.
Number of flushes
But not only the timing of the harvesting itself has an impact on the shelf life but the number of flushes as well (Figure 11). While this test was done at room temperature, it still indicates that for a second or third flush, the discoloration is higher than for the first flush.
Stipe Trimming
The fifth factor is stipe trimming. Stipe trimming is the process of cutting off a portion of the lower stipe and the attached mycelium and casing material at harvest. Some mushroom growers instruct pickers to leave as much lower stipe as possible on the fruiting bodies (up to about 35mm) to maximize yield and consequent economic return.
However, one noticeable feature of harvested mushrooms during storage is the elongation of the stipe; hence, mushrooms with short stipes results in proportionally less stipe after storage when compared to mushrooms with initial long stipes.
Therefore, some growers trim stipes closer to the cap to minimize the change in appearance after storage.
To paraphrase Ajlouni[11] “Recently, experiments in our laboratory have demonstrated that trimming stipes closer to the cap at harvest can also improve postharvest shelf life.”
Mushrooms were harvested from the first flush at the MTDF by four different methods as follows:
- SS (short stipe)-stripes were trimmed to 5mm immediately at harvest.
- LS (long stipe)-stripes were trimmed to 30-35mm immediately at harvest.
- SS2 (short stipe cut twice)-stripes were trimmed as LS at harvest and then trimmed again like SS about 3 hours later before packaging.
- Whole-mushrooms were pulled from casing and were not trimmed but package with some mycelium and casing material attached.
The results of this test can be seen in figure 12. While after 3 days after the harvest, all mushrooms were had still the same maturity index and color (L) both parameters changed after 6 days and 9 days respectively.
Figure 12: Influence of extent of stipe trimming at harvest on postharvest shelf life of mushrooms stored at 13°C in PCV overwrapped packages as indicated by (A) cap development and (B) browning (decrease in L). Whole: whole mushroom picked; LS: trimmed mushrooms to long stipe; SS: trimmed mushroom to short stipe; SS2: mushrooms trimmed twice[12].
This impact can even be seen visually (Figure 13).
Figure 13: Photographs of mushrooms with stipe trimmed to 5 mm from the cap and those with stipes left untrimmed (35 mm) after 6 days storage at 12°C[13].
Washing solutions
As mentioned earlier, the shelf life of fresh mushrooms may be limited by bacterial spoilage or enzymatic browning, depending on condition at harvest and on handling and storage conditions. Hence washing mushrooms to remove adhering compost or casing residues produces an attractive product for the fresh market but may accelerate browning or development of purple blotches.
But washing also predisposes mushrooms to spoilage by Pseudomonas tolaasii and other bacteria because of mechanical injury to the mushroom surface and water absorption that results in high internal humidity. This defect is described as “brown” or “bacterial” blotch.
Therefore, researchers starting to develop washing solutions to prevent this spoilage. One of them Hughes described in 1959 a washing solution containing 0.05% sodium metabisulfite and 0.05% sodium chloride that could be used to clean mushrooms without aggravating browning.
However, the treatment of mushrooms with sulfite is no longer permitted (FDA, 1986).
Another washing solution containing hypochlorite was only partially effective in delaying spoilage. Hence the research continued and found that hydrogen peroxide vapor which has been used to sterilize medical supplies and equipment, aseptic packaging systems, and fresh table grapes is a useful tool.
During my research I found two other washing solutions which:
- 1% H2O2 + 0.1% EDTA (McConnell 1991)
- 3-5% H2O2 + dipping in a browning inhibitor (Sapers 1994, 1995)
I took the results of the first scientific paper (Table 1) and put them in a spreadsheet. In doing so, we can easier see the different effects of the washing solution.
Table 1: Effect of H2O2 and browning inhibitor dips on discoloration of external mushroom surfaces during storage at 4°C[14].
As table 2 indicates, adding H2O2 and browning inhibitor to water reduces the number of lesions.
Table 2: Influence of different washing solutions (translation of table 1).
The next results were that increasing the additive (0.2% cysteine*HCL + 0.1% disodium EDTA) has no impact (Table 3).
Table 3: Influence of different additive levels on the number of lesions.
On the other hand, increasing the H2O2 content increased the browning (Table 4).
Table 4: Influence of different H2O2 levels on browning.
The last thing which we can learn from this first test results (Table 1) is that using 0.1% NaCl instead of the combination of 0.2% cysteine*HCL + 0.1% disodium EDTA makes no difference. But the access to NaCl (salt) is way easier throughout the world than the access to HCL and EDTA.
Table 5: Comparison of 0.1% NaCl and 0.2% cysteine*HCL + 0.1% disodium EDTA.
Besides testing different washing solutions, the researcher also tested the duration of the wash itself (Table 6). Again I transferred these results in my own spreadsheet to increase the visualization of the differences.
Table 6: Effect of H2O2 concentration and treatment time on storage stability of whole mushrooms at 4°C[15].
Table 7: Translation of Table 6.
As table 8 clearly shows increasing the time of the wash itself from 30 minute to 45 minute (+ 50%) increases the lesion on day 8 and browning on day 0 after the wash.
Table 8: Influence of the time on the number of lesions and browning.
If we increase the H2O2 concentration from 3% to 5% it reduces the lesions on day 0 and day 8, as well the browning on day 0 (Table 9).
Table 9: Influence of different H2O2 concentration on lesions and browning.
If we increase at the same time the H2O2 concentration from 3% to 5% and the washing time to 45 minutes we see an increase of the lesions on day 8 and the browning on day 0.
Table 10: Influence of the time on the number of lesions and browning at different H2O2 concentration.
Packaging
The next factor on our list is the packaging itself and to be more precise the atmosphere the mushrooms are stored in. As mentioned in the beginning, the O2/CO2 ratio has an impact on both the respiration rate and the transpiration rate.
While the respiration rate is the intake of O2 and the output of CO2, the transpiration rate indicates the water loss of the mushroom.
It could be found that the magnitude of reduction in respiration rates and the delays in the onset of the respiratory climacteric is proportional to the decrease in O2 concentration and the increase in CO2 level (Table 11).
Table 11: Effect of CA composition on respiration rate of mushrooms. The mushrooms were stored for 7 days at 10°C under various CA and RR was measured under air at 10°C after removal from CA cell[16]
To make this effect more visible, I translated the results from table 11 into a plot (figure 17). As we now can see, the higher the CO2 and O2 content within the atmosphere, the higher the respiration rate and vice versa.
Figure 17: Effect of CA composition on respiration rate of mushrooms[17].
To reduce the transpiration rate researcher started to use, for example, sorbitol in packages. It could be shown that mushrooms which were packed with 15g sorbitol per 100g mushroom in a polystyrene tray and wrapped with PVC had an improved L value and a lower maturity index in comparison with the control (Figure 18).
Figure 18: Effect of sorbitol on the maturity index of mushrooms during storage in conventional packages at 12°C (largest standard error of mean = 0.183)[18].
For further readings about How to Store and Transport Your Mushrooms Properly. I put some great information together in this article. The article talks about different kinds of packages and the latest development in research.
In the following video, I talk about a research project which investigated the use of different modified atmosphere packaging material and their influence on the shelf life of mushrooms.
Storage
And finally, storage in general and the storage temperature precisely. As you learned throughout this article, storing mushrooms at a lower temperature improves the shelf life of them. This is as mentioned due to the effect that at lower temperatures, the metabolism of the mushrooms is slowed down.
This impact can be seen in figure 19. Here the mushrooms which were stored at 5°C are showing a slower cap development than stored at 18°C. At 5°C, they reached after 7 days a cap development index of 3 while at 18°C this index was already reached after 1-2 days.
Summary
Having these 8 aspects
- Mushroom strain selection
- Additives to the irrigation water
- Harvesting time
- Number of flushes
- Stipe trimming
- Washing solution
- Packaging & packaging atmosphere
- Storage
in mind and acting on them helps you to provide your customer with a better experience and quality. In doing so, it positions yourself against your competitors.
Everything you just read is part of the How Do I Increase My Mushroom Yield? If you want to read more about that, just hit the link to my article. In it, I address the four factors, strain, substrate, supplement, and spawn rate.
With that said I hope you found this article helpful. See you on the next page.
