Fruit Glue

While the idea of gluing fruit together may sound novel, it was pointed out that the process is nothing more than an extrapolation of a fruit terrine.  Still, we find that the ability to layer fruits and vegetables together is really exciting.  Especially when we look beyond using just gelatin, which is the traditional bonding agent in fruit terrines and only effective at cold temperatures.  Instead, we were inspired by the synergy of hydrocolloids.  The first combination of ingredients we played with utilized the gel which occurs when alginate is introduced to a calcium.  The product, which acted as the catalyst for our ideas, was designed for gluing meat pieces into uniform blocks, cylinders and whole new structures.  The product consists of two components, one a sodium alginate and one a calcium lactate.  While the idea of using these two ingredients to bind proteins was interesting we were more excited by its other possibilities: binding fruits and vegetables.

We tested the theory of using the combination of these two ingredients to glue planks of melon together.  The adhesive worked and the results were a beautiful terrine.  Then, we heated the melon terrine.  It held, the glue kept the pieces of melon together through the cooking process.  As it turns out the reaction between alginate and calcium is thermo-irreversible.  (In fact, we already knew this, though we did not pay it much attention in the beginning.  Remember to pay attention to all the details throughout the process of any experiment, as it will only save you time and effort.)  We were thrilled with the results and equally full of dismay.  The dismay was generated because at that moment we were reliant on a proprietary blend of alginate and calcium to create our bonds. Obviously the next step would have to be to create our own blend.  While we began thinking about the alginate-calcium reaction it dawned on me that we should try using LM pectin and calcium.  We know the reaction forms a thermo-irreversible gel.  Also, to our taste, pectin and calcium seem to form more palate friendly gels.  The release of flavor is cleaner and more forward, while the gel itself is delicate and soft.

With both the alginate and pectin ideas to work with we set about a few tests.  I also dropped an email to Wylie to ask for his thoughts and help in testing our ideas.

I began with what we had in our kitchen, sodium alginate and calcium lactate/gluconate.  At times I am my own worst enemy.  I was starting to conduct tests with an unknown alginate and a blend of calcium sources, where I did not know the blending ratios.  Thankfully my attempt at using these ingredients as glue failed and the failure was a whack to the side of my head.  With failure leading the race I set about getting several varieties of sodium alginate, to create a firm strong gel and a medium firm gel.  We also needed pure calcium sources and we looked towards calcium lactate and gluconate.  We felt both varieties would be necessary depending on our applications.

Since I was waiting on alginate and the calcium arrived first, I started working with the pectin.  In order to answer a number of our pectin questions I gave Ted at CP Kelco a call.  Thankfully Ted was locked out of his car and had time to discuss our ideas and approaches.  Once Ted answered a few of our questions, we set about applying the idea of fruit glue to pectin.  Along the way we had a few flops, although each failure was successively closer to the desired end result.  We were also lucky to have Wylie testing out his versions in his kitchen and sharing the process, this way we only had to make half as many test runs on our own.

It turns out that both pectin and alginate form bonds which will hold fruit together and which are thermo-irreversible.  We found the alginate bond to be a bit more gel like and slightly stronger than that of the pectin.  Yet, the pectin gel is seamless and the flavor of the gel itself is tasty and has great mouth feel when and if you realize it is there.

As it turns out, the approach to both using the alginate and pectin is quite similar.  It seems that the calcium reaction would be at the root of the similarities.  To begin with, we make fruit solutions with .5% calcium lactate or gluconate.  The choice of one over the other is based on taste.  The reason for making a flavored solution is to boost the taste of the final gel.  Once the solution is made, we vacuum seal the fruit to be glued in the calcium solution.  This impregnates the fruit with calcium.  It takes about five minutes for the calcium to be absorbed by the fruit, after which time we open the vacuum bag and pat the fruit dry.  For a LM pectin application we dissolve 3% pectin in water at 95ºC to hydrate it and then cool it down.  Once the pectin is cooled, we brush it on one piece of the calcium infused fruit and lay another piece on top.  Then we vacuum seal the fruit to compress it together and let is rest in the refrigerator overnight.  The following morning when we cut open the bag, we will find that the fruit has been sealed together with a pectin gel.  In the case of the alginate we dust the calcium soaked fruit with sodium alginate and vacuum seal the fruit together.  There is enough moisture in the fruit to hydrate the alginate and allow the reaction of calcium and alginate to occur.  Once again we let the fruit rest overnight to allow the bond to fully occur.

We are simply at the beginning of what we consider to be a ground breaking idea.  While the initial outlook may be just an extension of a fruit terrine we believe the integration of pectin and sodium alginate as bonding agents for fruits and vegetables is truly remarkable and the possibilities are endless.

Currently we are also working with these ideas in pureed fruits and vegetables to see what is possible.  Time and our imaginations will see what we come up with next.