I wasn't happy with the 4% honey liquid culture (LC) recipe, which is recommended by most people. So I decided to try out a few popular recipes and share the results with you. Turns out 0.75% light dry malt extract (DME) works best. It's not exhaustive but a good start I'd say. But see for yourself.
Reasons why I don't like the 4% honey recipe were a slow growth and bad visibility. The first time I recognized mycelium was after 1.5 weeks. In addition, there are sediments after pressure cooking. You can filter out these sediments and pressure cook again, but who wants to do that much work.
So I set out to the www to pick five popular LC recipes for my little study. The candidate LC recipes were 4% honey, 4% maple syrup, 4% light corn syrup, 0.75% light dry malt extract (DME), and 5% DME (1 teaspoon DME is 4g). The LC's are topped up with water to 100% (weight percent).
Protocol: Five pint jars were filled with the respective candidate ingredient and filtered water (Brita filter, to filter out chlorine, mycelium doesn't like it), to give 400 ml total. A magnetic stir bar was inserted into each jar for mixing. Each lid had a hole sealed with micropore tape for air exchange and a self healing injection port (not used here). Each LC solution was stirred on a magnetic stirrer before pressure cooking yielding a homogeneous solution. The jars, whose tops were covered in aluminum foil, were sterilized in a pressure cooker for 15 mins at 15 psi. After cooling down to room temperature the jars were inoculated with a ~0.5x0.5cm piece of agar colonized with psilocybe cubensis (B+ strain) in a clean glove box. The solutions were kept at room temperature ~70F and stirred twice every day for about a minute. The pictures below show the liquid cultures after five days (sorry for the quality).
 Pictures in this order: 4% Honey, 4% Maple, 4% Light Corn, 0.75% DME, 5% DME
 Table: Qualitative comparison of liquid culture recipes, on a 1 to 5 scale, with 5 being the best. DME: light dry malt extract. Weight percent.
I was most happy with the 0.75% light dry malt extract solution. It's not so clear in the picture but the mycelium was clearly distinguishable despite a few sediments. It also showed the fastest mycelial growth. Neither maple nor light corn syrup had any sediments and the mycelium was easy to identify. Growth rate was also good for these two candidates. 4% honey and 5% DME had many sediments so visibility was impaired, and they didn't show any sign of growth after 5 days. After a week there was growth in honey and 5% DME, it's just slower compared to the other candidates.
Wild speculations:
In my limited understanding the optimal sugar to water ratio is what matters most for mycelial growth. The sugar contents of honey, maple syrup and light corn syrup and, light dry malt extract are 81g, ~68g, 56g and, ~60g per 100g respectively. So for a fair comparison the sugar content would have to be equal for each LC.
Just to confirm that theory I'd like to see a chart for each ingredient that shows mycelial growth versus ingredient content in water. Maybe there's room for improvement. Light corn syrup or maple syrup would be good candidates as they didn't show any sediments after pressure cooking.
Another aspect to consider is the antimicrobial property of honey. On one hand it slows down mycelial growth, however it might keep contaminants out in the long term. But I'm only speculating here. Maybe someone smarter than me can weigh in here.
Edited by deda_mraz (05/17/20 08:35 AM)
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