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Mushroom Yield and Biological Efficiency

Mushroom yield and biological efficiency are important parameters that need to be understood and optimized by the mushroom cultivator. When you first start out growing mushrooms, you might not be all that concerned about how many mushrooms you get. At first, just getting some nice looking fruits is a huge success! But as you get more proficient at growing mushrooms- and especially if you want to turn your hobby into a business– you should be increasingly concerned about how many mushrooms you can grow with the substrate you have.
Pink Oyster mushrooms after harvest, ready for the frying pan!

What is Mushroom Yield?

Put simply, mushroom yield is the amount of fresh mushrooms you can produce with your space, substrate and other constraints. The larger your yield, the more cost effective your grow. Yield should be determined using the total weight of fresh mushrooms from all flushes until the substrate block is completely spent. You may find that the yield for your mushrooms can vary wildly between flushes, which are why using the total yield is a better indicator of performance. That being said, it is sometimes better to go for a larger yield on the first flush, and future flushes may have diminishing returns.

What is Biological Efficiency?

Biological efficiency, often referred to as BE, is simply a way to calculate the effectiveness of a mushroom strain and substrate combination when growing mushrooms. It is a measure that was originally developed by the button mushroom industry in order to grade certain strains of mushrooms.
By definition:, 100% biological efficiency occurs when 1 lb of fresh mushrooms is harvested from 1 lb of dry substrate, over multiple flushes.
BE=(weight of harvest / weight of dry substrate)x100%
Because the calculation uses the weight of dry substrate, it is possible- and actually quite common – to achieve a biological efficiency greater than 100%. The calculation uses the weight of all mushrooms harvested from a substrate over multiple flushes. The fact that the calculation uses the dry weight of the substrate throws many growers off, since much of the weight of a fruiting block or straw log will be water. Usually it easier to weigh your fruiting container after it has been inoculated and compare that number to weight of fresh mushrooms harvested. Although this is not technically “biological efficiency”, using the “wet-weight” it is still a useful measure for mushroom growers to quantify the efficiency of their grows.  

An Example of Calculating Biological Efficieny

Let’s say that you are able to harvest 2lbs of King Oyster mushrooms from a 5lb supplemented sawdust fruiting block. Each fruiting block contains 1.4 liters of water, which weighs about 3.1 lbs. Therefore, the total dry weight of the substrate is 1.9lbs. In this case the BE would be 105% (2lbs/1.9lbs), and the wet-weight efficiency is 40% (2lbs/4lbs). These numbers are vastly different in magnitude, but are representing essentially the same thing. One reason that true BE is important to understand, however, is because this number is what is commonly reported by spawn producers as a way to grade certain strains of mushrooms. You can use this number to predict how many mushrooms you can grow for a given weight of bulk substrate.
A nice harvest of King Oyster Mushrooms.

Expected Yields for Different Mushrooms

Different mushrooms, and different strains of the same species, will have a wide range of potential biological efficiencies. Typically, Oyster mushrooms which grow well on straw, such as Pearl Oysters and Blue Oysters have a high BE. More delicate mushrooms, such as yellow oysters and slower growing mushrooms, such as Reishi, tend to have lower BE values. Let’s look at some different mushrooms and their BE’s, and expected yields.
blue-oyster-mushroom-yield BLUE OYSTER B.E.:100-200% Yield: 6-12 lbs from a 25 lb straw log, up to 3 lbs from a 5 lb supplemented sawdust fruiting block. king-oyster-mushroom-yield KING OYSTER B.E.:100-150% Yield: 6 – 8 lbs from a 25 lb straw log, up to 2.5 lbs from a supplemented sawdust fruiting block. PINK OYSTER B.E.:100-170% Yield: 6-10 lbs from a 25 lb straw log, 2.5 lbs from a supplemented sawdust fruiting block. lions-mane-mushroom-yield LIONS MANE B.E.:90-140% Yield:Up to 2.5 lbs from supplemented sawdust fruiting blocks. reishi-mushroom-yield REISHI B.E.:80-120% Yield:1.5-2 lbs on a supplemented sawdust fruiting block. yellow-oyster-mushroom-yield YELLOW OYSTER B.E.:50-90% Yield: 4-8 lbs from a 25 lbs fruiting block, up to 1.5 lbs from a supplemented sawdust fruiting block. shiitake-mushroom-yield SHIITAKE B.E.:100-200% Yield:1.5-2.5 lbs on a supplemented sawdust fruiting block.

How to Increase Mushroom Yield

There are a number of different ways to increase your yield and make your mushroom harvest more fruitful, more efficient and more profitable.

1. Choosing a High Performing Strain

The strain you choose for your grow can have a huge impact on yield. Different strains within the same species of mushrooms can produce vastly different results. Think for a second about the mushroom life-cycle. A mushroom culture starts when the hyphae of two compatible germinating spores mate and start to grow out as mycelium. This means that when starting a grow from spores, there are untold gazillions of different possible combinations or “strains”, all with minute genetic differences that can have an impact on yield. Luckily, top-performing strains have been carefully developed and optimized over the years to produce good and reliable yields. These strains are preserved as cultures, which are commercially available. Of all the factors involved in trying to maximize yield, choosing a good producing commercial strain is probably the most important.
Different strains will have different yield characteristics.

2. Supplementation

Supplementation is the process of adding a nitrogen rich nutrient to the mushroom substrate in order to increase the potential yield. This works by providing the mycelium with a larger nutritional base in which to support stronger mycelium and produce larger, healthier fruits. Supplementation is usually achieved by adding bran to the substrate, typically wheat bran or oat bran. Adding too much supplementation, however, will actually have detrimental effects. With increased supplementation comes the increased probability of contamination, and thus diminishing returns on your yield. Use supplementation carefully, starting small and increasing slowly to achieve optimum results. In a way, increasing your spawn:bulk substrate ratio is a way to increase your nitrogen content, and is a form of supplementation. Again, too much spawn will eventually lead to diminishing returns. You need to find your sweet spot.
King Oyster Mushrooms harvested at different stages of growth.

3. Timing Your Harvest

When you choose to pick your mushrooms obviously has a huge effect on overall yield and biological efficiency. Picking mushrooms when they are small, such as Agaricus species in the button stage, will decrease your BE. Picking mushrooms late will allow for a larger overall yield, but the quality of the mushrooms may be less due to the fruits being past their prime. Every cultivator should be able to find the sweet spot for when to harvest their mushrooms in order to achieve the best yield for the desired quality. The right time to harvest mushrooms will depend highly on the species of mushrooms, and the different ways you plan to store your mushrooms before consumption.
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