I normally make kombucha with regular white sugar (sucrose), and I’ve made a few batches using glucose as the carbon source for the microbes. This time, I used half-sucrose, and half-glucose. Once it was done, I flavored it with hops.
- 14 days: pH 3.2. Mild flavors all around, despite the acidity, though it did have a light fizziness. I decided that I didn’t really want the acidity to go below 3.2, so I bottled it.
This was the first use of my new autosiphon, and it worked beautifully. I decided that the mild flavors would make for a good test of different hops varieties, so I bottled 1 pint plain, one with 1 oz Motueka, one with 1 oz Vanguard, and one with 1 oz Simcoe. Daughter #2 likes the plain, but I find that to be drinkable but uninteresting.
- After 7 days steeping, there was a marked difference between the three varieties of hops.
- Motueka: light bitterness and relatively fruity.
- I added 1/8 tsp gypsum to 1/2 qt.
- I should have split this so that I could taste some with and without gypsum side by side. As it was, I think the hop flavor may have been a bit more focused and clear, but I’m not sure.
- This was most like when I’ve used Mosaic hops, but with a more subtle flavor. In the end, I can’t think of any reason I’d choose this variety.
- Vanguard: sharp, woody bitterness that lingers for 15-30 minutes. This flavor was relatively unpleasant, and doesn’t blend well with other flavors.
- I added 1/8 tsp gypsum to 1/2 qt.
- I should have split this so that I could taste some with and without gypsum side by side. As it was, I think the hop flavor may have been a bit more focused and clear, but I’m not sure.
- I won’t be trying this again.
- Simcoe: strong bitterness that seems most stereotypically beer-like of any of the hops I’ve tried. The bitterness lingered, but no so long as to be annoying.
- I eventually combined the bottles with Motueka and Simcoe, and that flavor combination worked pretty well. I used that to create a few 50/50 blends.
- Apple kombucha 1: This worked pretty well.
- Apple kombucha 2: This was a sweeter blend, and didn’t work so well for me.
- Inulin: This worked well, though not quite as well as it did with the yeast nutrient.
- Yeast nutrient: this worked really well.
- Two of these had added gypsum, which might help the hops taste cleaner, crisper, and sharper.
- Motueka: light bitterness and relatively fruity.
I’m finding that this sugar formula makes a nice clean base for hops. It’s not the most interesting, but it allows the differences between different hops varietals to show, and it blends will with other, more interesting kombuchas.
:| 
I have another question, if you don’t mind. Seeing that a fructose polymer like inulin/Jerusalem artichoke extract and black tea substrate apparently works, I wonder what a glucose polymer like potato starch/potato extract would be like as a substrate! Do you think the microorganisms in kombucha can break down starch sufficiently?
I might try this when I get enough scobys.
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Thanks for the comments, I’m glad to know someone finds it useful. I hadn’t heard of fermenting stinging nettles, do you have any online references? It sounds like something I should be able to find dried in bulk, and it should be easy enough to whip up a 1 quart batch.
I’ve gotten way behind in blogging about what I’ve tried, but next up is fermented inulin. I’m not sure what the final fructose content is (though I’ll be referencing a study), but I can’t taste any sweetness at all. I hadn’t thought of potato. I have no idea if starch will work, but I’d think it should be easy to test. More ideas for to research… :)
You may have already read that I don’t always use a scoby when starting a new batch. If you want to try new things without risking your scoby, I’d suggest mixing some portion of your four current batches, and using that to inoculate the “risky” experiment. I find 1/4 cup kombucha starter is sufficient for a 1 quart batch, or 1 cup kombucha for a 1 gallon batch.
I’ve not done much with long-term sustainability testing, really only my sans-scoby series. But I always cycle everything successful through my scoby hotel, solera style, so it can change over time but I think the chances are low that I’ll ever kill it off.
Will you be documenting results anywhere? I’d be interested in reading about it.
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Looking forward to your next writeups!
I continued reading about starch fermentation after I wrote that comment, and I’m quite certain that in home ferments (in contrast to an experimental, non-food lab setting with rare microbes) the only way to ferment starch without using added amalyse/amylase-rich malted grain is to use amylolytic fungi such as the ones present in Asian rice/cereal ferments. A search for koji and jiuqu is a good starting point in exploring the different amylolytic molds and yeasts, the major of which being Aspergillus oryzae. They saccharify starch to enable glucose fermentation. It is necessary to gelatinize the starch prior to fermentation.
I live in Norway (hence my interest in potatoes and stinging nettles!), so getting hold of koji or jiuqu might prove a challenge, but at least now I know how to begin my potato experiments. The cultures are sold on ebay and Amazon, but I haven’t found anyone shipping to Norway yet.
I have dry stinging nettles in the cupboard, so we’ll see who manages to get some experimental results first 😉 It’d be great if we both gave it a shot. Thanks for the tip on fermenting without a scoby. I don’t have any handy now, I have only done microbatches and I’ve consumed it all, but I’m brewing up about 5 litres in total at the moment, ready in a week or two.
I won’t be documenting results anywhere at the moment, and they’d be in Norwegian in any case, but I’ll gladly posts some of them here if I find them noteworthy.
Here are some of the studies that put me on the trail of stinging nettle kombucha:
http://journals.sbmu.ac.ir/afb/article/view/11138
Click to access 1450-71881243051M.pdf
https://link.springer.com/article/10.1007/s13197-014-1648-4
I’m curious about the peppermint, winter savory and other herbs as well, but my intuition tells me they contain too much anti-microbial essential oils to support microbial diversity in the culture long term. I have no proof of this of course.
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Here’s some stinging nettle, by the way: https://no.iherb.com/pr/Frontier-Natural-Products-Organic-Cut-Sifted-Nettle-Stinging-Leaf-16-oz-453-g/30938
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I just got back from my local coop, where I noted that they have potato starch, but not nettle leaf. Frontier Coop is carried at several local stores, and it seems likely that one of them will have the nettle leaf.
I can get a 1oz bottle of amylase from my local homebrewing shop for $1.09, there may be a similar inexpensive option near you. It’s not as sustainable as a fungal culture, but easy to experiment with. But your scoby may already contain what it needs, and there’s a cheap and easy way to find out! I’ve been surprised at how flexible my kombucha culture is.
Aspergillus Niger is the dominant microbial contributor in the production of Puerh Tea. It look like A.N. produces produces amylase and protease, so it may be interesting to add some Puerh to a batch, if that’s easily available. However, I seem to recall that A.N. can also produce butyric acid, which is unpleasant, so make sure you avoid cross contamination until you’re sure you like the results. I have a block of Puerh in the cupboard, and it’s on my long list of things to try.
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This was my first comment that didn’t seem to get through:
I’m reading about your experiments with great interest. I’m experimenting with dextrose at the moment and currently have a 2/3 dextrose, 1/3 sucrose batch, a 50/50 dextrose/sucrose batch and a 100 % dextrose batch going at the moment. About 7 % sugar and green tea as the substrate. The prior batch was 50/50 dextrose/sucrose, with a scoby aquired from a friend who used sucrose and green tea.
I’m a novice kombucha fermenter (these are basically my first batches ever), but I take a great interest in microbiology and the science behind kombucha fermentation. My goal is to produce a pleasant, dry kombucha with low amounts of residual sugar and as little total fructose as possible, and preferably with a diverse microbial population. It should ideally be a sustainable culture that can reproduce itself just as well as a normal kombucha culture. I’d be happy to hear any insights you might have about how I can achieve this.
I’m also interested in trying other substrates than tea, and in the literature I’ve seen stinging nettles mentioned. Have you tried this? I imagine the high nitrogen and mineral content of nettles would support proper kombucha fermentation. It’d be great to use a native plant.
I’m excited to try out your cocoa kombucha recipe!
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Alright, I’ve sampled this round of experiments after 9 days of fermentation.
I used pure dextrose powder and pure sucrose powder, and green tea for #1–3.
#1: 50 % dextrose, 50 % sucrose. The pellicle was about 1 cm thick, firm, white and opaque. Some sweetness and mouthfeel, tart taste, quite regular kombucha aroma. A bit vinegary.
#2: 70 % dextrose, 30 % sucrose. The pellicle was about 0,5 cm thick, firm, white and opaque. Trace of sweetness although quite dry, very mild taste. Thin mouthfeel, rather uninteresting. Not very vinegary.
#3: 100 % dextrose. The pellicle was about 0,5 cm thick, firm, white and opaque. No trace of sweetness, very dry and mild. Thin, watery mouthfeel, very little aroma, an uninteresting taste. Not very vinegary.
#4: 1/3 dextrose, 2/3 sucrose, black tea. The pellicle was about 0,5 cm thick, semi-firm, white-spotted and transparent. Quite sweet tasting, full bodied, with regular kombucha aroma and taste. Too sweet for my taste. Pleasant acidity.
The high-dextrose batches stood out by having a rather watery, thin mouthfeel, while the low-dextrose batches had more residual sweetness and a more viscous, pleasant mouthfeel.
There was very little acetic tang in the high-dextrose batches. I suppose it’s a successful attempt at creating a dry kombucha, but it was not a very palatable beverage. I’m going to try a second ferment with some berries, haven’t done that before.
I’ll cook up some nettle kombucha with some different sugar setups in a few days.
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Thanks for the report!
Your findings seem to mirror my own with regard to the effect of glucose on flavor, mouthfeel, and acid production. You may find your happy medium in acidity, mouthfeel, and dryness by using a higher proportion of sucrose, but less sugar overall. Maybe #1 slightly less sugar and fermentation time, or #4 with less sugar and more fermentation time? You could also take #1 and substitute some of the green tea for a nitrogen source that may cause the production of citric or lactic acids in place of acetic.
Your batches finished far more quickly than mine typically do. I’m curious if mine is simply slower, or if you prefer less acid production. Personally, I don’t find gluconic acid (or lactic) to be very interesting flavors, so I let mine ferment long enough to have a definite acetic bite.
Do you have access to litmus paper or some other way to measure or estimate acidity? Since different acids have widely different detection thresholds and flavor profiles, I find ph measurements really helpful in tracking what’s happening beyond my ability to taste it. In some cases, I found that the transition from kombucha mildly-flavored to one that was obnoxiously-flavored was just a couple days of late-produced acetic acid in addition to the existing gluconic acid. I think I can prevent crossing that threshold by measuring pH.
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Alright!
Results are in for the nettle tea experiment, at least for the first generation. I’ve been away on holiday so the ferments have been going on for longer than previously, 31 days. I think they came out good so I’ll take your advice on leaving my kombucha to ferment longer in general.
I boiled the nettle tea for a few minutes and let it cool down for 6 hours before straining. I used about 8 grams of dried nettle leaf for 2,5 litres of water. The tea had a dark brown earth-like colour. All the ferments have turned translucent with a light, golden colour, so nearly all of the pigments have been metabolized.
Nettle tea #1: 100 % dextrose, about 7 % sugar to tea ratio. Produced a very thick and dense scoby, half an inch to an inch thick. The taste was only a little bit sweet, it had a thin body and mild acidity. The taste itself was rather pleasant.
Nettle tea #2: 50/50 dextrose and sucrose, about 7 % sugar to tea ratio. Produced a thick and dense scoby, although not as thick as the other two. The taste was slightly sweet, it had a bit more body, and tastes slightly less acidic than #1 (probably due to the sweetness). The overall experience was not as good as with #1.
Nettle tea #3: 50/50 dextrose and sucrose, 10 % sugar to tea ratio. Scoby thick and dense like #1. Sweeter than the other two, and with a significant acetic punch. Rounder body, offset by a lot of fizz that must have developed under the thick scoby acting like a tight lid.
I don’t think the trace sweetness complements the general characteristic of the nettle brew, I think the taste profile became a bit flat. I preferred the 100 % dextrose variety with little trace sweetness which let the subtle natural aroma of the brew shine through. Actual tea has a lot more aroma that wrestles nicely with some trace sweetness, but nettle tea just doesn’t have that and becomes overpowered in my opinion.
I will continue this purist experiment of brewing kombucha on nettles only.
I don’t have any litmus paper at home, and I don’t think I’ll prioritize getting any either, but I certainly would use them if I had some on hand.
I also did a second ferment with blueberries (bilberries), and had some great results taste-wise and with carbonation, so that was a lot of fun.
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