Tropical Fruit Forum - International Tropical Fruit Growers

Citrus => Cold Hardy Citrus => Topic started by: jim VH on December 22, 2020, 10:18:28 AM

Title: Kabosu
Post by: jim VH on December 22, 2020, 10:18:28 AM
Kabosu is one of the three citrus commonly used by the Japanese to create Ponzu sauce, along with Yuzu and Sudachi.  Kabosu is said to be closely related to Yuzu.  The Yuzu is quite hardy in the Portland Metropolitan area, easily surviving freeze in January 2017 where the temperature dropped down to 8F (-13.3C) and the temperature never rose above freezing for 14 days.  Because of the close relation I was wondering if the Kabosu was also as hardy, but was unable to find any definitive  information.

So, a few years ago I found a Kabosu at Mckenzie farms.  It was, unfortunately, on a Citrange rootstock  These rootstocks do not survive the extended freezes here in the Portland area, and in fact the rootstock did die in January 2017.   Before the rootstock died, however, The top looked pretty good, with little defoliation and no obvious damage.  This gives hope for it's hardiness.

Fortunately, with foresight, before that freeze, I grafted the Kabosu onto a Poncirus Trifoliate (PT ) rootstock and put it in the ground and it is now about 4 feet tall.

( (

This is also the first year with a significant crop of fruit, 22 in total.  Three were given away, the remaining 19 weighed a bit over 4 lbs (1.8 Kilos).  Segments of the fruit are surprisingly sweet, given that it is an acid fruit.  About grapefruit sweet, without the grapefruit bitter.  The flavor is milder than a Yuzu without the slight 'skunk' that some people find offensive.  It would make a good Meyers lemon substitute, with some extra overtones that- not being a gastronomical expert- I won't attempt to describe.  The fruit also appear to be larger on average than the Yuzu, as shown in the image.  From left to right below are

Kabosu   Yuzu  Sudachi

( (

The fruit are surprisingly seedless, with only two fruit out of the 19 having seeds for a total of six.  Shown below are a few of the fruit and a ruler, with three cut open.  For comparison, at the bottom are also a cut open Yuzu and Sudachi.

( (

The fruit were then converted to marmalade, a process which involves separating out the juice, membranes and peels.  I took advantage of this by measuring the Brix level of the juice with a calibrated wine testing hygrometer and the acid level by titrating 15 ml of the juice with a o.2N NaOh solution.  The results are :

           Brix:  10.2%
           Acid level: 4.3%
           Sugar to Acid ratio:  2.37

When I sampled the juice I found it quite sour, which made me wonder why a fruit segment tasted so sweet.  So I sampled some of the chopped up membranes and found them quite sweet, with surprisingly little bitterness compared to most citrus, including the Yuzu and Sudachi.  I then sampled the chopped up peel and found it also relatively sweet and low bitter, though not quite as sweet as a Kumquat.

It made four pints (4 lbs.-"a pints a pound the world around") of very good marmalade, which tastes like lemon pie..  The nice thing about marmalade is that there is very little wastage. 

So now I wait for the next arctic blast to test the hardiness.  A significant freeze typically comes along every three-four years here, so we're about due.  But of course, they don't come along on demand, unless you can borrow a very large freezer, so it may be a while to know for sure.
Title: Re: Kabosu
Post by: Sunmicroman on December 22, 2020, 02:27:16 PM
Nice Kabosu write up Jim. The fruit you gave me was pretty good, nice mellow lemon flavor with no off flavors.

Awesome about the marmalade. Sounds great.

It also seems to be a good candidate for long term in our Pac NW climate. I look forward to hearing how it continues to do for you over the years and might give it a shot in my yard too.
Title: Re: Kabosu
Post by: tedburn on December 22, 2020, 02:31:17 PM
Thanks, very interesting topic and very good explanation. So Kaboshu, if similar cold hardy to yuzu could also be a good choice for middle Europe. But I'm currently not sure if Kaboshu is sold in Europe. At least it is not widespread.
Title: Re: Kabosu
Post by: SoCal2warm on December 23, 2020, 12:24:44 AM
I personally sampled one of the fruits from jim VH. The peels of the fruit were moderately edible, in fact I kind of enjoyed eating, or at least nibbling, on them. They were not as soft/edible as Yuzu, but definitely more edible than regular lemon or mandarins.

When I first cut into it, I noticed it had a smell like a very high quality Meyer lemon (maybe a little bit better) mixed with some very aromatic Satsuma smell. There might also have been a tiny hint of Yuzu aroma in there, barely on the edge of being perceptible.
The inside is a little bit more fragrant than a lemon.

Eating it, it tastes like a lemon. It's not bad at all, but it doesn't have the most flavor, maybe not the best quality lemon, kind of watery, maybe just a little insipid, mixed with a little bit of tangerine and Satsuma flavor.

Keep in mind, in Japan the fruits are usually picked green when they are more sour.

The inside part of the fruit is not bad, but in my personal opinion the peel is where most of the flavor is, for Kabosu. It's a similar situation for Yuzu.
Title: Re: Kabosu
Post by: Ilya11 on December 23, 2020, 04:16:51 AM
Thank you very much for a detailed report. I was never aware of sweet taste of internal membranes of Kabosu. I also noticed that older leaves are yellow now. Is it a regular feature of this variety?
Title: Re: Kabosu
Post by: jim VH on December 23, 2020, 10:00:57 AM
Hi Ilya11,

No, I think the yellowing of the older leaves in the winter seems to be a general feature of the climate here; Pretty much all the citrus at my place do that to one degree or another.  Some, like Satsumas don't have quite so much.  Others, like seem to have it more.  The Kabosu is about in the middle. 
The effect is more profound when the tree has a heavy fruit load.  In that case even the newer leaves can yellow up in the winter to a lesser degree.  Come spring, the newer leaves green up again and the older ones fall off.