Longer pre-wetting of straw to preserve structure during mushroom composting

In my 'Pre-wet' blog, I already wrote about the importance of pre-wetting for good mushroom substrate. In this blog, I would like to discuss the structure of straw. I often hear customers say: "We are shortening the pre-wetting time because the structure of the compost is too short." But I disagree with this statement. Why? Read all about it in this blog.

If the straw has a shorter pre-wetting period, the micro life is less likely to damage the hard wax layer of the compost. The idea is that the straw and, therefore, the compost stays longer.

The problem lies in the machines that process the straw. Proper mixing is done by rapidly rotating shafts that pick up the compost and spread it mixed, to optimise blending. Hard straw breaks in these machines, however, which results in shorter structure.

Further opening up the straw, by way of a longer pre-wet or by adding an additional dose of water a few days after the start of the pre-wet, softens the straw. Softer straw breaks less easily and therefore retains more structure.

We can compare straw with spaghetti. If we want to put spaghetti in a small pan, we can break it and it will fit, but the structure becomes shorter. Allowing the spaghetti to warm up a little first makes it soft, so you can get all the spaghetti into the pan without breaking it.

If the growing room is filled while there are still yellow straw sprigs in the compost that have not been opened up, this is a problem. The water is not absorbed by the compost; and in addition, the mycelium literally cannot grow in the straw. This prevents the mushrooms from getting any nutrients from the straw. You also continue to see the same yellow straw sprigs in the compost in the second/third flush. Non-opened compost only provides filling weight, but the mycelium cannot feed the mushrooms from it.

Mark den Ouden

Mollier Diagram

Jun 29, 2022

What is the absolute moisture content of the air? Or the enthalpy of the air? More and more growers have a handy app that reads out these values. I always ask: “What do you do with this data?” I don’t always get an answer. Because it’s not about the numbers. The best way to understand this is to use a sponge as an example. It’s much clear and you can combine it with the Mollier diagram. Use this link to download the coloured Mollier diagram (pdf).

A sponge?

Air can be compared to a sponge. As air cools, it shrinks. This means its holds less moisture. The same thing happens if you squeeze a wet sponge. So how does this work in the Mollier diagram? Trace the blue line straight downwards and the diagram will literally show you what happens. The temperature drops and the RH rises. Following the lines in the Mollier diagram gives you insight into what happens to the climate. Simply reading values in an app doesn’t give you the same understanding. My philosophy is to draw lines on the diagram. Doing this will teach you much more about the effects on the climate that just reading some figures!

Conclusion: download the Mollier diagram and place it close to the climate controller so you gain a better understanding of what the climate controller does. If this doesn’t work, there are two options:
The basic settings in the climate controller are incorrect. In my consultancy role I often ask: “Why is the growing room climate set this way?” The answer is sometimes: “The computer controls and regulates the climate”. But who controls the computer? You do, so you have to understand how it works! If not, ask your advisor or installer for help.


You don’t understand fully how the Mollier diagram works. For a good, step-by-step explanation take a look at chapter 6 about the Mollier diagram in the Mushroom Signals book. This chapter clearly explains all the principles of how to read and understand the diagram.

Mark den Ouden, Mushroom Office

Picking mushrooms is more than just removing them from the beds. The handling and picking the right mushrooms is vital. Creating space to allow them to grow bigger is not only for yield. A mushroom with enough space has better evaporation and will hold the quality better, longer and will have a better shelf life as well. Handling of mushrooms can affect quality and shelf life.

Damaging mushrooms at picking is affecting the quality on the shelves and can be avoided by good training and supervision of the pickers. Especially at the start of the flush when the mushrooms need to be separated damage is easily done. At that stage it is important that the focus is on the quality of separation instead of the speed of picking. Separation needs time and the picking will be low. At some farms pickers are being paid at an hourly rate, which will get the pressure away of making the right amount of kilos and let the picker focus on the quality of the separation. As you can see on the picture below is what is commonly seen after separation.

  image 2019 01 17 2


With removing just a few mushrooms several others are damaged and will never grow to top quality anymore.

What is a good separation? Well, of course that depends on what kind of size of mushrooms you want and also on how many pins are developed. When you want big sized mushrooms of course you give them more space and when you aim for smaller sized mushrooms, leaving them a bit tighter will be more beneficial. What really matters is the way you do the separation.

In practice it happens often that too many small mushrooms are being picked to separate where they could have got the same result with picking less.

First rule for the separation is; always pick the mushroom in the middle of the tight area. When you do that you will see that with just picking one single mushroom you can create space for many others around. When you still see lack of space, of course you pick more but start from the middle and you will minimize the numbers of mushrooms you need to pick to separate. Which size is getting picked while separating is not the main thing, as long as you only pick from tight areas.

Once the space is created we have to allow the mushrooms to grow to their maximum size to get a good yield. However, that means we need to pick them exactly on time if not we will lose the quality. Therefore, many farms trained the pickers the selective picking method. That means selecting the right mushrooms to pick and leave the others to give them the change to develop more. That we can achieve by over picking rooms several times a day and every pass pick the biggest mushrooms away and create space where needed. Harvesting all day mushrooms of 60mm is achievable if done in perfection. A mushrooms doubles in size every 24 hours, and will grow in weight 4% every hour, in weight, not in size. Doing a pass every 2 hours can give stunning results and can be done a lot easier with electric picking trolleys. A good planning need to be made for every picking day to ensure to have the right amount of pickers. Short of pickers can cause quality loss, too many picking cost yield as the mushrooms don’t get the time to grow to their full potential. Make the right choice daily!!

Just to get an idea of the growth of the mushrooms. We all know they double in weight every 24 hours. That means that we get 4% extra every hour, look at table below how that develops with a single mushroom of 40mm, that on average weights 22 grams.

40 mm = 22 gram = 100 %
45 mm = 28 gram = EXTRA 27 %
50 mm = 34 gram = EXTRA 54 %
55 mm = 40 gram = EXTRA 82 %

So we get 27% more weight from each mushroom if you let it grow 5mm more. Looks clear to me that it will be beneficial to do more passes on a daily base and let the mushrooms, that have space and are still strong enough, grow. Of course only if you did the right separation at the start.

Making a good harvesting team is therefore very important and every farm needs a good leading example with eye for the details to lead that process. A good harvest management can make or break all the efforts from earlier stages. Training and a good system will bring you many advantages and a quality that stands out. Every farm should have a designated trainer that will train new pickers into perfection. Remember that it’s easier to train a new picker when you spend the time then retrain pickers with bad habits.

Erik de Groot

GLAGS Global Agriculture Services

This email address is being protected from spambots. You need JavaScript enabled to view it.

Glags logo

My previous blog described what the pH should do during the composting process. This blog examines the role of the raw materials, such as ammonium sulphate, gypsum and water.

Ammonium sulphate, (NH4)2SO2

During indoor composting, NH3 is removed from the air by a reaction of the air to sulphuric acid, H2SO4. The by-product resulting from this process is ammonium sulphate, (NH4)2SO2. ammonium sulphate can be added to compost as a source of nitrogen. This reduces the pH value of the compost.


What is the principle property of gypsum? The acid binding capacity of gypsum neutralises the pH in the compost. So what does gypsum actually do? Gypsum also makes the chicken manure less sticky. The advantage of this is that the manure can be mixed through the decomposed straw better. The gypsum ensures the compost structure stays open and airy and is less inclined to become anaerobic. As the previous blog explained, this is a very important condition to ensure the pH falls during the process.


Gigantic amounts of water are applied during phase I. The moisture content of the straw rises from 5- 20% to a moisture content of 74- 76% at the moment of filling into the phase II tunnel. That moisture is created by the added water. The pH of the water therefore has a far greater influence than you might think.

Rain water/groundwater

If a lot of rainwater, with a pH of 6 or even lower, is used during the rainy season, and more groundwater, with a pH of 7, during the dry season, you will also notice that the pH value gradually changes over time. The water is recycled at the composting plant, which explains the gradual change.

Anaerobic water

If the recycled water, or process water, is stored in a reservoir, it must not be allowed to become anaerobic. If water does become anaerobic, all the micro-organisms in the water will be destroyed and the pH value of the process water will fall sharply. This will cause poor results at the end of the composting process.

Mark den Ouden

It looks like we are not going to have any winter this season in Europe. On the contrary. It is very wet and humidity is very high.
This has its reflection on compost and casing.
If raw materials for compost are stored outside or under just a roof, they are evaporating less water and in the same time some materials get wet by the rain.
If the materials are not checked regularly (meaning every batch) before they are going into the system the compost manager cannot interact on this. If the composting is not adjusted this will result in a few percentage points more moisture. By itself no problem at all If the grower knows about it.
It gets more difficult though if also the casing is getting wetter.
As a normal result of the rain the peat gets wetter during storage.
And many casing yards have a big stock laying outside. Because of expected frost during winter they tend to build up stock. A normal procedure every year around this time.
Getting a casing wetter during production is fairly easy. But getting it drier is more difficult.
Mixing in dry white peat is normally the answer but this generally results in a finer mixture which most growers do not want.
Result for many growers is that first flushes have problems growing out. The numbers are too low and second flushes have a problem with quality. They mature too fast and picking time is too short.

So what can be done?
If a grower knows the compost is already a bit wetter he can adjust the watering schedule immediately. Less or no water during filling and a change in schedule of watering on the casing during case run.
Also the filling can be changed technically. A wetter casing can be more lumpy or even slightly anaerobic. Especially if casing is stored a while before filling.
It is possible to run the caccing spinner a bit faster to open up the layer of casing. More caccing, by putting the spinner deeper, is not always necessary. Caccing more has a fairly big impact on the growing.
At the same moment the levelling spinner should run slower to create a sort of “digging” effect. This is done to keep the surface of the casing open.
After filling and casing the total amount of water can be around 20 to 25 litres per m2. Depending on the amount of mycelium that is desired.
In outgrow make sure enough fresh air is taken in. especially on day 7 of the break this is essential. Rooms which have a hard time in growing out have a very low demand for fresh air because of lack of activity of compost. Make the minimum fresh air setpoint is at least 15%.

At the end of a year or at the start of a new one it is always a good thing to look back and forward. Look at it as an evaluation and re-focussing of targets. It is also a good time to give yourself and your team a feedback.
Looking back to 2021 it was a year of great challenges. We had our normal variations in compost and casing soil quality. It still is impossible to predict the weather so we still will have to cope with changes in raw materials due to the weather. And reacting to that always comes too late.
Another thing that kept us busy was Covid. Supermarkets stayed open but restaurants and hotels got closed down. For those delivering mushrooms to that restaurant sector life was hard. Due to that closure the demand of restaurants almost fell back to zero for those places who did not do food deliveries at home. Read catering. On the other hand, due to the closure of those restaurants the supermarket sold more. People preparing their own food tend to use more mushrooms in a dish. So farms who depended on supermarket supply had a benefit there. Plus we had the effect that people where looking for healthy food. The only thing was that demand was unpredictable. Sometimes supermarkets demanded a lot, sometimes they just cancelled the orders. A reason for that was the government of each individual country. The rules where different everywhere and nobody knew what was coming the next week. This was also the reason that many farms got in trouble with their workforce. Depending on foreign labour, many farms did not know if they had the pickers for next month. A test for negative result in their home country made sure they could come to your country. But on entry of the country or even your farm another test often gave another result, resulting in a quarantine for a week or so. A positive result on the test had big negative effects on the farms concerning picking. Another result of covid was that consultants like me had great difficulties traveling and visits where often cancelled. The sparring simply did not take place and many developments on farms where put on hold.

Look forward though we are facing a lot of challenges again. Covid will not go away for a while so restrictions will stay in place. A good reason to look very critical at the labour supply of the farms. Other countries? Fixed contracts to keep people there ? Find people in your own country despite of the mostly higher costs? In that case security of labour comes with a price but at least with a steady labour base. Already announced are the higher energy costs which will have an effect on the whole business. Because of transport costs rising everything will be more expensive. Direct energy costs will rise so your cost price will go up.
Talk to your clients about that before it really turns into a problem. Make good prognosis and a business plan based on the new situation. Experience of last year has learned me that supermarkets do think with you as long as you can present good figures, based on facts. So keep an eye on the ball and remember. Act before it is too late and do not act on emotion. Remember, you make a good product and they need it.

This leaves me with wishing you all the best for 2022. If traveling restrictions will loosen up we will probably meet again physically, if not we always have zoom.

Henk van Gerwen
Akkie's tuin

Cookies make it easier for us to provide you with our services. With the usage of our services you permit us to use cookies.