Rehydrating beans - any experience?

[nrdlnd]

Hi and a Happy New Year!
This has been up before in a couple of threads. I didn't take it seriously as I thought I had fresh beans. With a roast a week ago I noticed that the roast didn't work as expected. The beans were "left overs" from 2019. They didn't develop so well inside. I have more beans that are becoming "old" as the pandemic made me buy more than I needed as I thought there may become a shortage of coffee.

@benjaminfleon mentioned rehydrating coffee when he introduced his Raost profile. He gave a link: https://christopherferan.com/2021/03/15 ... -protocol/ . In this link the author recommends to rehydrate coffee to about 16% humidity to get better taste. In the trade it isn't it recommended that green coffee should have more than 12% humidity. In the article he gives an example howto humidify beans from 9% to 16%. I have no moisture meter (yet!) so I supposed what was left of my beans had that humidity so I added the water needed in a container with the beans and waited 9 hours before roast. I used the same amount by weight of the beans as 10 days before but in reality there were less beans and more water of course. I used the same D-Light profile that I had modified with a different fan profile to lessen the power demands as I'm on 230V (not 240V). https://kaffelogic.com/community/viewto ... =318#p2320

The screenshot of the roast with this 2019 bean is with a washed Peru Tropical Mountains that was roasted 7 days ago. The ROR curve is X5 on the Y-axis and the smoothing is the default 30 sec. I've had a discussion with @Geronimo in another thread about the smoothing and I think it could be of value to have less smoothing maybe below 15 sec or even lower to more easily see changes in the ROR curve. This roast is modified by me to suit beans for more normal moisture beans (10-12%) and I think it looks rather ok.

211226_PeruTropicalMountains2_D-Light1Fanmod_1.png (74.96 KiB) Viewed 6609 times

This is the roast today with the rehydrated beans:

220103_TropicalMountainsRehydrated.png (73.95 KiB) Viewed 6609 times

This is a bit different. The important developing phase after 1st crack looks very nice with the rehydrated beans but the ROR is dipping a bit before 1st crack and I can see the need for some modifications. The profile used has a second +2 zone but it needs to be extended to between 5-6 minutes and the third -3 zone should start directly after that. I think this could make the ROR curve even better even if it's already nice after 1st crack.
EDIT 4th of Jan: Both roasts were 100g. The drier beans lost 14.5g in weight. The rehydrated beans lost 21.3g. They had got 8g water 9 hours before the roast. If I subtract the water did the rehydrated beans loose about 1g less in weight. The end temp for the dry beans were around 219 C and for the rehydrated around 217 C. This difference can explain the difference in weight loss. Both roasts were stopped around DTR 21%. The rehydrated got a lower L=1.4 and the dry beans L=1.7 (mean of two roasts). The two roasts look very similar Light/Med Light. They are both evenly roasted inside maybe the rehydrated a little more even but its difficult to see any differencies. The rehydrated beans seems to be a little bigger in size after the roast.

Rehydrated_beans.JPG (102.25 KiB) Viewed 6595 times

I tasted the dry beans today 9 days after the roast and they had a nice acidity, rather nice sweetness, some fruit and the taste hold together after the coffee had cooled. Actually the coffee (drip coffee) tasted better than expected. End EDIT
Anyway it will be interesting to taste and compare the two roasts. I will taste the first roast and in about a week the rehydrated roast from today and take notes. It's not possible to make a blind taste. I have no more of this bean but I have other beans that are becoming out of date. If I want to take this further I may need a moisture meter. I will see if I can find a not so expensive one. Any tips?

[nrdlnd]

Is there any physical differencies between the two roasts? I had a feeling that the size differed and that the rehydrated beans may have "swollen" and became bigger because of more steam enlarging them. I measured 20 beans from each batch and I couldn't measure a significant difference. When I cut the beans to see if they were evenly roasted inside I noticed a difference. The rehydrated beans were more evenly colored inside (slight) and they kept together better when I cut them in half. They seemed to be more homogeneous. Rehydraited beans to the right.

Rehydrated_beans2.JPG (98.36 KiB) Viewed 6588 times

I also have a picture of two cut beans and the rehydrated bean to the right. Maybe it's difficult to see but the rehydrated bean is slightly more homogeneous in color.

Rehydrated_beans3.JPG (78.39 KiB) Viewed 6588 times

What I can say this far is that there is a difference between the two roasts. They are not quite comparable though as it was less beans and more water in the rehydrated roast and the end weight became less beacause of that. I can't for sure say if it was the difference in the amount of beans or the rehydration that made the differences I have observed. The batch size by weight was the same. The rehydrated beans were more evenly roasted and more homogeneous in color and consistency (the differencies are slight but observable by eye). I have tasted the bean without rehydration as filter coffee after 9 days rest and it tasted good much better than I thought it should. I will taste the rehydrated coffee one week from now but can't make a direct blind comparison. For that I need to make more roasts and I also want to have the ability to measure the moisture of the beans before i add water to moisture them. This time my assumption was that the moisture of the 2019 beans were around 9% and I added water to get 16% moisture. This moisture level was recommended in the above article but fresh beans usually shouldn't have more moisture than 12%. I will come back to the taste of the rehydrated beans.

[nrdlnd]

I couldn't wait one week before tasting the roast with the rehydrated beans so I made a test today as filter coffee. The beans had 2½ days rest. The same grind setting as with the original drier beans and 20g.

The original brew weren't bad and I wrote 2 days ago: "I tasted the dry beans today 9 days after the roast and they had a nice acidity, rather nice sweetness, some fruit and the taste hold together after the coffee had cooled. Actually the coffee (drip coffee) tasted better than expected."

This is my impression today of the rehydrated beans: "Taste after 2½ days rest. A lot of taste and very fruity and also sweetness. No burned taste. Will taste again in about 5 days or more." Well this is very promising. I really enjoyed the coffee I made today! Hours after I can still feel the sweet taste!

I will try to find a moisture meter. The well known brands are very expensive so I will probably go a middle way and buy a cheaper alternative but from a supplier with a good reputation. It's almost impossible to find good tests or reputable reviews from these cheaper devices. A possibility is to go to a commercial roastery and calibrate the device against their professional device.

[nrdlnd]

My first experience rehydrating beans went well. I tasted them after 2½, 5½ and after 7½ days. The best was after 2½ days when it was more fruity and sweet. It was also very good after 7½ days.
Yesterday I prepared two batches 100g Sidamo Wendo beans. I had a moisture meter and added water so the beans got 15% moisture. I made 5 measurements of the beans before adding water and they varied about 1% and I used the mean value to calculate how much water I should add. After about 12 hours in a closed container I had 200g of beans with 15% moisture. I noticed that the first cracks came at a lower temperature than usual and I had to wait to get more concecutive cracks. It could be the Sidamo beans as they have varying sizes. I had made some changes with the zones and the log of the two roasts looked rather ok but I want to make more adjustments.

I tasted one of the roasts after 4½ hours with a V60 like brew and it was one of the best results that I have got from this bean and this was only a few hours after the roast. It was medium light. Balanced acidity, fruitiness and a nice aftertaste. I was very sweet. The Sidamo beans are known for their sweetness but I have never tasted them this sweet. Edit 220115: I tasted the other roast after 24 hours rest. It was not as fruity and sweet as the first roast. I have not adjusted the scale for roast degree. The first roast stopped at L=1.3 (215.9 deg C) and the second at L=1.7 (219.2 deg C). I should have cupped both yesterday after the roast. The developing is happening very fast in the developing phase. There were only 33 seconds between the roasts. The first roast became medium Light and the second Medium. The difference in end weight were only about 0.5g.

I think this could be a way to standardize the roasting process if the beans have about the same moisture content when you start the roast. It seems to have other effects also. The higher humidity may affect the caramelization of the sugars. I don't want to publish the profile now as I'm working with it and have made some changes that I haven't tested yet. I'm coming back when I have more experience!

[Geronimo]

Hi

Great reading on your rehydration testing.

Assume you found an affordable moisture meter, and if it is an affordable device, can you let me know what you purchased please. I don’t want to have to sell a kidney for one.

Cheers
G

[nrdlnd]

No I did bite the sour apple and bought one of the more well known meters. First I decided to buy the meter that is recommended in the link above an Agratronix 08150. I had to buy it from the US. I then got a good price on a Wile 55 when I bought it together with some other equipment. It did cost me about the same as the Agratronix but it's a product from Finland and I live in Sweden. Easier if something goes wrong. I think these meters are rather similar maybe the Agratronix is more advanced. I could have bought a meter from China for 2/3 of the price. I still have my kidney ! It's important to follow the instructions how to measure and preferably make several measurements. It varies some between the single measurements. I think it's important that the beans and the instrument has the same temperature even if the instrument has temperature compensation. I still think it could be a good idea to calibrate the meter at a professional roaster. Now in the beginning I rehydrate to 15% to have some margin. In the article he recommends 16% (or even 16.8%). This evening I will make a new roast with another bean and the moisture differed +1.5% compared with the roast a couple of days ago even if this bean was older. I thought it should have been the opposite!

[Geronimo]

Hi

Thanks for useful information. Makes sense to buy a reputable device, better long term reliability investment.

Cheers
G

[nrdlnd]

Hi again @Geronimo,

Very nice that you are following this. I made the roast this evening that I prepared in the morning. This time with another bean I wanted to experiment with as I wrote before. This is an older bean but also Ethiopian a washed Yirgacheffe grown at a similar altitude as the Sidamo Wendo I roasted before. I dehydrated it from 11.4% to 15% moisture and used the profile modified after the former roast. 1st crack came at a lower temperature and was more difficult to "nail" compared to beans that aren't rehydrated. The development seems also to be faster and I stopped the roast at a lower temperature. This must be aneffect of the heating being more efficient with more hot steam. I think the roast this time became light instead of medium light. End weight was also higher. DTR was around 21%. This is very interesting as I've had difficulties roasting well developed light roasts before. There were a tendency to a crash and a flick at the end. Otherwise the curves looked good. I don't think this affects the taste very much. Anyway I've made further changes with the profile and I've prepared a new roast for tomorrow. The roast I'm preparing for tomorrow had 11.5% moisture after three measurements compared to 11.4% for the roast I prepared for today. That's very consistent. I added 4g water to 96g of beans to get a 100g batch with 15% moisture.

I really recommend reading Christopher Ferans blogs (link above). He seems to be using hot air/fluid bed roasters similar to the principle of the KL. This is a lot of fun and the coffee taste good!

Cheers,

[Geronimo]

Hi

I read the linked article, and looked at prices of the moisture meter you got, and the Agratronix. A bit more than I expected, therefore might have to put on next year’s Christmas wish list.

Cheers
G

[nrdlnd]

Hi Geronimo,

Yes the meters are rather expensive but green coffee is also expensive. If you can make the roasts taste even better and if you can restore stale beans then it may be worth it. As Christopher Feran says beans are best dried to 10% moisture as they keep better. He says the beans need more moisture during the roast to get more taste and restoring their original taste. Is it possible to get more consistent results? I want to see if this is true.

I'm just in the beginning trying this out and I've used a profile I've had good results with before but I've had to to modify it when I use dehydrated beans. This profile is rather power hungry and with dehydrated beans it needs even more power. Just now I'm using the last beans of a washed Yirgacheffe to adjust the profile. I've never liked this bean very much but I can use it to experiment with. I'm also going to try it rehydrated with another profile I've had good results with before. This profile is less power hungry and that means more margins for the roaster. Later on I will try cuppings.

Cheers